Damp - Cellar Waterproofing and Tanking

Water seeps into our cellar

Q We moved into our end of terrace Victorian house 2 months ago. The cellar was damp when we moved in and since then we have had a lot of rain. There is a drain in the cellar floor which is working fine. The small walled front garden has a natural arched drain hole in the gate post; there is also a wall which is midway from the front wall and the house. When it rains the garden seems to be holding water and coming back through the cellar wall. At the side of the garden is a very small path and 3 steps up into the house, in the cellar underneath this area water is permanently dripping in onto the concrete. What is the best way to rectify the drainage at the front of the house? Next doors cellar is dry. This must have been happening over a long period of time as a lot of the mortar between the bricks on the front cellar wall is very soft like putty.

A You will appreciate that it is very difficult for us to visualise the situation you describe thus our ability to offer advice is limited. From what you describe it sounds like you need the services of a ground work company to install some land drains to divert the ground water. Have a word with your local authority and see if they can provide you with some names. Failing that do nothing as what you are seeing has probably been this way for many many years - what you do depends upon what you want to use the cellar for.


Split level waterproofing

Q We live on the south-facing slope of a Wealden clay hill in a 1920s semi-detached brick cottage with external cavity walls.  The rear half of the house has a solid floor and the front half has a suspended wooden floor. We are thinking of adding a two-storey extension to the side of the house and, because the house is on a slope, we'd like the extension to be built on a slightly lower level (we'd have split level home). There appears to be a, probably bitumen, DPC around the outside of the existing house which would be above the level of the floor of the extension. We do have a slight problem with some dampness in the existing house i.e. those connected to the solid floor. How could we successfully deal with damp-proofing the extension and protecting the existing house from damp. I would appreciate your suggestions.

A There are many products and systems that cater for the split level situation you describe so do not let this worry you or put you off. Your architect should advise you what should be used (it's dependent upon site conditions) then if it does not work he is held to account.


What is the hole size for a sump?

Q What is a typical depth and diameter of the open hole in the cellar floor prior to inserting the pump, gravel and equipment etc.

A A regular sump/pump/gravel chamber built into a cellar floor would require an opening in the floor of between 650mm and 750mm square/diameter/cubed. The sump should also be fixed into position otherwise there is a risk of it 'floating' up.


Damp cellar - where to begin?

Q I have just recently moved into a 1900 Victorian Terrace. I don't know where to begin with the cellar as some of the walls are a bit damp. I am only going to use it as a games room. I had a damp course done 6 months ago. The walls where it got replastered looks like they have dried out but they have bits of crystal on, what does this mean? Also the old paint that was already on the walls is starting to bubble and flake off, again I'm not sure what this means? I will be buying a dehumidifier but not sure what type/size I should get. I eventually want to repaint all the walls but not sure what procedure I should be doing! I would appreciate any advice you can give me. Thanks

A By cellar we understand this to mean an area under the house with some of the walls, if not all, earth retaining. As a consequence to provide dry wall surfaces it is necessary to either tank or dry line the walls from floor to ceiling which should be linked to a waterproofed floor. A remedial DPC in a cellar situation is seldom of much benefit. The white crystalline deposits on the surface of new plaster are probably sulphates which are present in most building materials, especially finish plaster. They usually form as the new plaster dries and may be brushed off. If they keep appearing it means water is continually evaporating and greater investigation is needed. Old paint bubbling off walls in a cellar is usual as the walls are probably damp. A DPC injection will not stop this happening. A dehumidifier will do little other than remove moisture from the atmosphere - it will not suck moisture out from the walls of have any significant effect upon drying them. Have you had a chemical DPC injected in your cellar and does it have earth retaining walls? Let us know. What you are probably asking is if there is a short cut way to damp proof a cellar - the answer is unfortunately no. It has to be an all or nothing approach otherwise you will be wasting your money


Damp cellar may ruin my ceiling

Q Firstly like to say what a great website and the good advice offered!
Now to my problem. I have a 1900 house with a basement, which has a large grill for ventilation and beneath the grill is a board loosely covering the outside steps to enter the cellar. Water definitely enters the cellar this way but at the foot of the steps there seems to be 2 little wells for some form of soak away, which I think is then creating moisture under the cellar floor (which is made of some form of old stone bricks) and then making the floor very damp (i.e. cardboard left on the floor overnight well away from the steps was soaking the next morning) and seeming to dampen the walls also. I have just had a new cellar ceiling put up with plaster and am concerned about the damp ruining it as it appeared to do with the previous ceiling (which I believe was of original construction) Please can you advise me what course of action I should take as I do not have a clue?

A What you describe sounds like a typical old cellar - virtually all of which are damp so yours is no different. The situation has been as it is for over 100 years but you state the grill has boarding beneath? We may be misunderstanding what you mean but does this not interfere (restrict) with the ventilation? We do not understand why damp should ruin your cellar ceiling? Provided you are only going to use your cellar for storage of non perishable items it sounds very much like your cellar just needs to be better ventilated i.e. vents at the front and back to achieve a through draught. Keep items that might be affected by a damp floor off the floor.


Water is entering my cellar

Q Water is entering my cellar at approximately 3 feet below ground level at various places and running down the walls. This results in a small stream running along the ground and collecting behind the basement wall causing it to become damp. What may be causing this and what can be done to prevent it? Is it possible to somehow seal the walls or will the water have to be drained in some way?

A Water entering a cellar, such as you describe, is not unusual. Whilst it is possible, it is difficult to stop running water. The current 'popular' approach is to install drainage directed to a sump in which a submersible pump is installed to pump out the water. How involved you get will depend upon what you want to use the cellar for.


Cellar floods a little

Q Our house was built in the late 1800's, and has a cellar approx 5 ft wide by 15ft.  It has been split into 2 areas similar size. The main area has an asphalt floor, and the other (old coal store) old Yorkshire stone. The Yorkshire stone area now has water in it which only appeared last summer. We have had all the tests by the water company and environment health. They say it is possibly ground water. The water penetration is visible on the wall and in the gully where it stops.  However, the level of water never rises, but it leaks through to the other cellar which we use for storage. The place where the water gathers is approx 2 inches wide by 2 foot long. I can take the water out with a sponge, and the next day, it is full again, but never higher than what was there originally. Any ideas how we can stop this without a lot of expense?

A From what you describe it sounds like you need to install a sump and a pump in the stone floor area which would pump water away before it caused a problem.

Cementitious tanking?

Q Hi the house I hope to buy has damp in all walls and floors of the basement. Will tanking permanently sort this out? The quote I have received mentions 'cementitious' and not DPC. It comes with a guarantee though. Is this 'cementitious' treatment sufficient on all walls and the floor?

A Cementitious means cement based, probably in the form of a slurry. Correctly applied cementitious tanking should sort out a damp basement and a DPC is not normally necessary if full tanking i.e. all walls and floors, is being applied. Cement based systems are however prone to condensation, require a lot of preparation, cables/pipes cannot be concealed and you cannot puncture it to hang pictures, fit shelves etc. The most popular method used today makes use of Cavity Drainage Membranes which eliminates most of these problems. We suggest that you obtain several quotes for different systems.

Damp cellar now floods

Q We have recently brought a house and when we viewed it the cellar was damp. However, due to heavy rain it seems that the cellar has some water in it. I was told to put some plastic sheet (don't know the technical name) and concrete the floor which I have done. But now the water seems to be coming from the sides. I would like some advice as to what I need to do to get rid of this water problem as I want to turn the cellar into living space.

A Most old original cellars are damp. Some flood occasionally, some flood regularly and some have never flooded at all. It could be that yours is one that floods occasionally and when you viewed to property it was OK at that time. Laying a polythene membrane over the floor and concreting over it unlikely to change the situation.

As you wish to convert the area to living space you need to consult a cellar conversion specialist. Your proposed use of the basement area dictates that the level of dryness required would be classed as 'Grade 3 - Dry environment' as defined by BS 8102 - Code of Practice for Protection of Structures Against Water from the Ground. This is a British Standard that should, as far as practically possible, be adhered to by anyone converting basements into habitable space. To help achieve Grade 3 classification for the basement areas of the above property ventilation would also need to be incorporated into the design. If a contractor is not aware of BS 8102 - use another contractor.


Damp proof paint in a cellar

Q I have just used Wickes damp proof paint on the damp walls in my cellar. The walls began to dry out but recently I have painted the walls with emulsion paint and there seems to be condensation on the walls & floor & the paint has not dried. What can I do to prevent this? There is no ventilation in the cellar - would air bricks cure this?

A We do not know of any 'damp proof paint' that would control moisture ingress into a cellar in the long term. Damp proofing a cellar is far more involved than applying paint material from a DIY store. Ventilation in a cellar is very impotrtant and if introduced would very probably improve the condensation problem. What you do regarding damp proofing your cellar is dictated by what you want to use the cellar for.


How much should it cost?

How much should it cost?

A question we are frequently is asked is 'How much should it cost' to carry out different types of remedial treatment in a property. Experience shows us that there are regional variations but we also know that there are sometimes enormous differences between companies quoting for the same work. It is important in these circumstances to very carefully compare who is quoting for what and who is omitting some aspects of the work that others may be including. If you go to the articles section of this site and read Articles 4a - 4d inclusive we hope you will be better informed.

Larger organisations obviously have greater overheads than a sole trader and logically one would think this should influence prices but it is not always the case. So what is a reasonable price?

The price a contractor charges is usually made up of two elements: 1) The labour charge which normally includes all overheads etc. and 2) costs specific to the job such as materials, plant hire, rubbish clearance etc. Outlined below are three different trading styles for three different types of contractor:


1. The organised sole trader

Let us look at a sole trader who rents a small yard employing a labourer and his wife on a part time basis. He wants to earn £30K per annum, his labourer £17K and his wife £10K. If we now factor in all overhead costs associated with running such a business over a twelve month period a figure in the region of £85K would need to be generated for this type of business just to stand still.


If we now deduct holidays, bank holidays, illness provision etc this leaves our organised sole trader 44 working weeks to generate £85K. Divide £85K by 44 weeks and he needs to earn £1931 per week. Divide this number by 5 and he needs to earn £386 per day. It is important to remember however that this is just the 'labour only' element of the job. The cost of materials, rubbish clearance, plant hire etc. specific to the job would be in addition to this figure.


2. The less organised sole trader

If we now look at a contractor who works on his own form home with no yard, wanting to earn £25K per annum, cutting back on certain overheads and targeting to work 46 weeks in a year. He would need to generate somewhere in the region of £35K per annum in labour costs to achieve this. On this basis a day rate of £152 would be necessary plus materials.


3. The small organised company with four vans

Finally if we now look at a small organised company with a director/surveyor, one other surveyor, 2 office staff, five operatives and four vans. This company would need to generate £365K per annum in labour costs. However because the company has four working vans the day rate requirement would be somewhere in the region of £400 - surprisingly not too dissimilar to the organised sole trader in 1 above.


Timber preservatives and rising damp treatment fluids and creams are relatively speaking not very expensive. Cellar conversion work using membranes, sumps and pumps does have higher material cost content. To gain an approximate idea of how much a job might cost therefore depends how many man/van days the job will take plus materials. There is no industry set price per meter run of wall or square meter of surface to be treated.



There is water under my floor

Q My property has a 6' void under the floor similar to a cellar but I believe its purpose is for a soak away, as the property is at the bottom of a slight hill. There is permanently about 8 inches of clear water at the bottom of the void. Rainfall seems to have little effect on the level, and if I pump the water out it returns in a few days. There are no visible leaks down the walls so the water appears to rise from the concrete floor. Could this be the water table? If so could the floor level be raised to overcome the problem, rather than tanking the whole space?

A The void depth beneath the ground floor is usually dictated by site conditions during construction and is not usually a functional area i.e. a soak away. Water beneath a floor is not usually a problem provided the sub floor void is well ventilated. From what you describe is sounds very much like the water table but your local water authority is able to test the water to see if it is from the main. Provided it is well ventilated I would not worry. I have surveyed many properties with a similar situation and one Victorian property was actually built over a stream with no adverse consequences.

If you backfilled with pea shingle it would take many cubic metres and all that would be achieved would be to put the water out of sight - it would still be there. Tanking? From what you describe it probably does not justify the expense. Just make sure the ventilation is good.


There is a water trickle under our bathroom

Q Having just moved to a detached dormer bungalow we seem to have hit a series of problems. House was built in 1959 and has a cellar under the property which is sectioned off into the various rooms up above. At first everything seemed fine until we had a problem with blocked drains. My husband then discovered a pool of water in the room underneath the bathroom. We have eliminated many leaks from above and the drains have been cleared but we are left with a trickle of water coming into this room at ground level. Nobody seems able to point us in the right direction. Could it be drains, could it be ground water or could we have an underground spring and who can help us sort this problem? We live in the north east of England in Gateshead. PS problem is about 6 feet below ground level and we do have a damp course installed. Any advice gratefully appreciated.

A If the trickle is permanent then it is likely to be either mains water or natural ground water. If it were drains it would be intermittent, smell and be cloudy. You should have a drains test undertaken and have the water tested by the local water authority to see if it comes from a leaking main (tap water contains additives that water authorities are able to identify) If it is neither of these than all that is left is natural ground water. Provided it is able to drain away freely and subfloor ventilation is good this should not be a problem. If you are concerned you should get a structural surveyor to check that running water will not have a detrimental effect upon the footings of the property.


Do I have to have a sump and a pump?

Q First of all, GREAT resource thanks for taking the time. I have a small cellar (16'x10' under a small brick Victorian terraced house) that we want to convert to a usable room. Due to cost I want to DIY a CDM system but I'm not convinced about the need for a sump pump. The cellar is a little damp in one corner but never leaks and we get no real surface moisture and certainly no water seepage. The cost for me doing it myself is time and materials so if (as in a earlier answer you provided) we get a water table change or street mains burst, my cost for re-doing it would be the same again, I guess. Point is, I can understand the epoxy 'blocking' systems being prone to problems as well as causing moisture to move, i.e. perhaps upwards, but in a small space such as ours would we really need the sump pump to move just the inherent moisture? In the end, in our case, wouldn't it just be an expensive 'critical cover' backup and not really needed to keep things as they are? It's an old property so we must be in a 'status quo' level of dampness too? I have had three specialists around and all want to go sump pump and total costs @ £10k and up!! Interestingly one of them wants to dig up the brick floor and the other suggests not doing so (but will remove some for the sump pump hole).

A Whether or not you install drainage, a sump and a pump is entirely down to you as the property owner and paying client. However from a contractor's point of view he has a 'duty of care' to you his client and if he suggests a specification that does not take into account key points contained in BS 8120 - Code of Practice for the Protection of Structures Against Water from the Ground, he would be failing in that duty. If in the future your cellar flooded and he did not install a sump pump you would be all over him like a ton of bricks demanding to know why he did not suggest a sump and pump at the time of the initial design and installation. As the paying client it is all down to what you perceive the risk to be based upon information provided by the experts you consulted and your own knowledge of the property.

It is true that very many cellars are just 'damp' and never flood and as you state the sump and pump is there on a 'just in case' basis which some might consider to be an expensive luxury. If you decide not to install a sump and a pump and as a consequence the cellar floods you would have no one else to blame but yourself.


How do we fix cupboards to a tanked wall?

Q We have a tanked wall which we are now putting a fitted kitchen against. How or what do we use to fix the units to a tanked wall? Are there special fixings?

A The answer to your question depends upon the method of tanking that was used as well as the circumstances on the other side of the wall that you want to hang cupboards/fix units. If it is a cement based system you should have allowed for this by forming recesses at the points where the fixings would be and the tanking should have been taken into the recesses prior to the render being applied. You may then drill into the render to a depth not greater than the recess so as not to puncture the tanking medium. Difficult to measure up I know but this is how it is done. If it is a membrane system then additional studding should be in place behind the plasterboard to receive the unit fixings and take the extra weight. If neither of these options are available then you have a problem as obviously tanking should not be punctured.
Did the company who did the tanking advise not you about this? We suggest that you contact them. They should be able to form 'tanked' recesses for you.


Musty smell from cellar

Q I own a flat on the ground floor which has a cellar below it and constantly get a musty smell in the flat itself. I assume this has something to do with the cellar but what can I do about it. Help! Many thanks

A What you describe is a relatively common problem. Most old original cellars will have a musty smell however with ventilation this is not usually a problem. You should install plenty of air bricks in the outside walls to ventilate the cellar - this should solve your problem and will be good for the flooring timbers as well!


Which system to use?

Q We have a 16th century cottage, suffering damp in the kitchen and larder. Ground levels outside are above floor level, rising damp was treated 20 years ago but have been told the current damp is from penetrating damp although outside walls have been rendered in the past 10 years.  We have had three quotes one suggests treatment of salt contamination and re-plastering of the insides and another suggests a cavity drain membrane system with aqua channel drainage. Have you any opinions of the usefulness of the second system or which would be more appropriate. We would greatly appreciate any advice you have to offer to enable us to make the right decision.

A Which course of remedial action should be taken would depend upon the circumstances and as we have not seen it we are not able to advise. You say the external wall was rendered about 10 years ago but we assume that this stopped at ground level or just above thus offering no protection from penetrating damp beneath as a result of the high external ground level. How high above internal kitchen/pantry floor level is the external ground level? If it is not very much then the membrane and drainage system may be a sledge hammer to crack a nut.  A waterproof render would very probably suffice. If you let us know a few more details we may be able to be of more assistance.


Tanked cellar leaks - What to do?

Q My terrace house is circa 120yrs old with a reasonable size tanked cellar. I've only had the house for 18months and have no idea how long the existing tanking has been there for, however judging by the general wear and tear, i.e. cracks, would suggest 25yrs+. Due to recent heavy downpours water rose through the cracks in the floors - resulting in 1 inch of (clean) water. All very suspicious, considering I'm at the top of the village - I'm pretty sure this is due to a nearby new-build that has its soak away pointed in my general direction. Regardless, what to do?
1. Fill the cracks (I'm sure I can find some suitable filler from a specialist retailer) and add a tanking slurry over the top?
2. Remove the entire existing tanking (floor and wall) and re-tank myself (cement based)?
3. Add some sort of specialist waterproofing agent to the existing tanking (e.g. slurry, SBR), then an adhesive coating, and re-plaster/tank over the top? (Assuming it's not lime based). I am in contact with the original (family of) builders and could ask them what the existing tanking is made of? Your recommendations please. Not happy to CDM as I'd like to do the work myself as I'm an ex-plaster.

A If the floor is already cracked then no amount of patch repairs on the surface will last very long. Also if the water cannot make it to the surface then the pressure that it exerts beneath the solid floor could be considerable and heave/floatation could become an issue which may be why the floor is cracked now. Without seeing the situation it is not really possible for us to advise what to do.


Company did not comission their installation

Q We have recently had a sump pump and waterproofing system installed in the basement of a shop in Cheltenham. When the company finished the works all looked well, until the next heavy rain came. The basement flooded again. I asked for one of their surveyors to go take a look and he called me back to tell me that the gate valve was closed, but once opened the pumps cleared the water. This was never opened from when they installed the system. They never commissioned any of their work and are now saying that is not there responsibility. How do I stand in a case like this?

A Obviously we are not aware of all the circumstances but from what you describe it sounds like to company responsible for the installation was negligent in the execution of their work. It is usually standard procedure to flood test an installation to check that it works before covering it up with floors etc. We are not legally qualified so we would suggest that you obtain the opinion of a legally qualified person to advise you further.


Cellar with sump damp

Q We live in a mid 19thc weather board house with a cellar that has a sump pump installed. The cellar still seems damp. What is the best way to treat this? There is no damp proof course installed. Should there be?

A The most efficient way to create a dry environment in a cellar is to use cavity drainage membrane material in conjunction with drainage, a sump and pump. A sump and pump alone will not do much for the environment of the cellar other than pump out any water that penetrates. How far you go is dictated by what you want to use the area for. May be for your purposes all you need do is improve the ventilation? Do not panic about a damp proof course unless it is affecting the accommodation areas. If it is a 19th century property it has stood the test of time and what will be will be.


If we do not tank will the damp rise?

Q We have a cellar that is not tanked. There is evidence of damp on the cellar walls. If we leave the cellar as it is and not tank it, over time can the damp rise to affect the walls of the floor above?

A You do not state how old your cellar is but we shall assume that it is old. Most cellar walls are damp and it is probably true to say that most cellars are not tanked. The dampness in your cellar has very probably reached a "status quo" level of dampness and provided nothing interferes with this everything should remain as it is.
If you did tank your cellar then you would interfere with the "status quo" level of dampness by reducing or preventing evaporation and a consequence of this could be that moisture within the wall will 'move'.

To conclude, therefore, your cellar situation has very probably been the way it is for very many years and if anything different was going to happen it would have happened by now. If you do interfere with it, say by tanking, then you will have moved the goalposts and the potential exists for moisture within the walls to 'move' unless it is effectively contained. Just make sure that your cellar is well ventilated at all times.


Damp in coal cellar

Q I need advice on a property I'm interested in buying. It's a mid terrace with old coal bunker that is about 3' wide, the length of the living room approx 25' and goes approx 3' under pavement. It has had a new DPC but there is clear water in the bunker/cellar towards the pavement which doesn't look well sealed but I obviously will seal. My main concern is that everywhere has been moisture checked by my DIY dad and is fine EXCEPT the cellar, joists in the cellar and the stairs which show high levels underneath (inside cellar) and medium levels on staircase. The rest of the living room is concrete and bitumen. Will it cause major problems? Can I treat the cellar timber effectively? Will the timber always be damp or can I dry out and then treat the cellar timber and if so where will any moisture then go? I don't plan to use it for anything other than garage like storage. Or should I walk away?? Thanks

A We assume that the property is 100 years+ old since it has a coal bunker. All such coal bunkers/cellars are damp and this in itself is not unusual. Obviously all measures should be taken to prevent surface water draining into the bunker where it extends beneath the pavement. You should always bear in mind that if the timbers visible within the cellar are original then they have existed in that environment for as long as the house has been built, thus unless something different has now occurred there is no reason why this should change. The main cause for concern with any timber of increased moisture content is that of fungal decay and no single spray treatment of any timber preservative is sufficient to prevent this happening as the parts of the timber where it would develop initially are unlikely to be accessible for spray treatment purposes.

The most beneficial course of action you could take is to introduce as much sub-floor ventilation into the cellar area as possible and try to create a through-draught between the front and back of the cellar.  This should reduce the moisture content of timbers visible from within the cellar.

With regard to the standing water, you may wish to install a sump and pump to discharge this or alternatively just live with it but make certain that everything stored within the cellar is raised off the ground.


Q Thanks - that has set my mind at ease. As a preventive measure could I treat the visible timber like you would treat decking etc?? And could I paint/treat the brickwork to prevent any problems and make it less unsightly? If yes what products can you recommend?


A Preventative treatment against what? As previously stated the risk is one of decay and a spray treatment will not prevent this from happening - if it is going to happen. Painting the brickwork will not prevent any problems from occurring in a cellar - if you really want to do it uses a masonry paint but you will probably have to re-do it on a regular basis. It is just a cellar.


What sould I do with my cellar?

Q Great site to have found well done! My cottage has a part sunken cellar and was subjected to the summer floods. I am told by villagers that this level of flooding is unheard of and records suggest last time was 200 years ago (no proof of this!) However the cellar seems in normal times quite damp free and I would like to consider making it habitable. It is quite long but narrow say 18 feet by 10.  What would you recommend; Tanking or other water proofing and is there a rule of thumb to guesstimate costs?

A It would be wrong to offer advice on your best course of action without seeing the situation. You will probably be aware that two options are available 1. Cavity drainage membrane incorporating drainage, a sump and pump and 2. Cementitious tanking. By far the most popular method used to convert cellars today is cavity drainage membrane. It has many advantages compared with cement based systems. You should obtain the opinion of a CSSW qualified surveyor.


Should I fit a sump and pump?

Q I have been researching tanking & waterproofing cellars. We have an old Victorian house with a cellar and we had the gulley pots replaced when we moved in due to the wall at the front of the house being wet! This rectified the problem to a degree but not fully as the wall is still a little damp and you do see a wet line on the floor by the named wall. I was wondering as the cellar has a gulley pot in the basement floor & the pipe from it runs under the house to the drains at the rear could we eliminate the need for a sump and pump? Should we put in adequate drainage on the front wall floor to run to the gulley pot? Any advice would be much appreciated as hopefully we would only need to apply CDM .

A We would advise that a sump and pump is installed unless you are able to 100% satisfy yourself that the existing drain is satisfactory, it will remain that way and it is able to be serviced easily. The possibility of water back filling should also be considered. It is not what is happening now that you are catering for it is what might happen at some time in the future. A small additional cost now could save you £££s at some time in the future and you would kick yourself.


I want to tidy up my cellar

Q I live in a mid terraced house built in 1900. The house has a cellar, one wall of which is damp. When I purchased the property the original coal chute had been blocked up and dehumidifiers and an extractor fan were utilised to keep the moisture at bay. The walls are irregular stone and the floor is stone cobbles set in ash/mud. I would like to get the cellar to a reasonable condition (not the smelly damp condition that it is in at the moment) but my concerns are that if I fully tank the cellar then the damp can move to my neighbours, both of which do not have cellars, leaving me liable. I was thinking about partitioning the damp wall to approx 3/4 foot, having two periscope vents from the front wall to behind the partition and four slide vents to allow the air to get to the rest of the cellar. Could you please advise whether this a viable route to go down, if not what are my options.

A You will not 'drive' moisture into your neighbours if you tank your cellar so do not worry about this. We do not understand what you mean when you say 'partitioning the damp wall'. Do you mean construct a separate wall in front of the damp one?

How much effort you put in to making the cellar 'usable' depends upon what you want to use it for. If you just want to tidy it up and use it for odd storage then you might want to consider lining the walls and floor with cavity drainage membrane. You could overlay the floor with T&G chipboard or a screed and there would be no need to cover the membrane on the walls with anything.


Told my cellar needs to be sand blasted - what a mess!!

Q We want to convert a cellar room into a bedroom and have been advised we need to have the room tanked, for which we have been given a quote we are relatively happy with. However, the builder has said the cellar needs sandblasting before the tanking can take place. The sandblaster has said the process is very messy and the whole house (and neighbouring properties) will be affected and it is best to move out whilst this procedure is carried out. Moving out is not an option for us, nor is the option of the whole house being affected. Is it essential to have the cellar sandblasted before tanking can be done, and if so, can you recommend any other options other than tanking.

A If you are being told sandblasting is necessary we assume a cementitious tanking system has been proposed. This method of creating a dry living environment is being used less and less these days in favour of Cavity Drainage Membrane (CDM) systems. Cement based systems are prone to condensation, involve a huge amount of messy preparation, messy to apply, and make subsequent fixing of radiators, skirting, cupboards, even hanging pictures difficult if not impossible. CDM eliminates all of these problems and virtually no wall preparation is necessary - no sand blasting! It is also very clean to apply and work with. We suggest that you investigate this option and you should look at Safeguard Europe's web site as they supply CDM (as well as cement systems). They have good downloads and CAD drawings to look at. Let us know what you think.


Concerns - I'm buying a basement flat

Q I have recently had a survey performed for a house I'm buying, well a basement flat to be exact. The building is 120 years old but and has recently been re-decorated by a developer. The survey has highlighted damp within external and some internal walls. Could you advise on our next steps, as looking at the walls there is no signs of any damp, as recently (2-3 months ago) have been re-plastered. We have also been warned that the air bricks are above ground level and that there might be inadequate under floor ventilation. The surveyor has said there may be ducts from the air bricks that go down to sub-floor level. Is there anyway of checks if this is the case?  We are concerned about possible dry rot if there is no ventilation under the floor. The developer is saying there were no signs of damp during redevelopment; however should we still get someone in for an expert opinion?

A Our advice when buying a basement/semi basement flat is to be very very careful indeed. We would be particularly concerned if a developer has recently 're-decorated' and would naturally wonder what has been covered over - perhaps nothing but perhaps something. Basement flats are more prone to suffer more from the effects of condensation as they tend not to receive the benefit of sun light and the thermal gain from it. They can also suffer from rising damp and dampness penetrating from steps up to the main front door, external abutting walls, the consequences of leaking gutters, running overflows etc. Be aware that developers are there to make money and the more they spend on a property the less their profit.

We are surprised that there are still timber floors in a basement. Depending upon the property's situation many original basement floors have rotted away and have been replaced with solid floors. Is this not the case? Has the developer laid new laminate floors or something else over the original floors?  If so perhaps you should think why?
You should most certainly seek the opinion of damp and timber specialists especially if there are no guarantees. Make certain boards are lifted and sub floor timbers are examined. If the developer puts up resistance walk away - it will be cheaper in the long run. Sorry to be a doomer and gloomer


Flooding mansion apartment

Q A year ago we bought a lower ground floor apartment in a 17th century mansion that was renovated 2 years ago. During a recent bout of heavy rain we noticed foul smelling water coming into the living room floor (which is about a metre below ground level). Apparently the outside drains were blocked and this has now been dealt with. The builders that renovated the house tell us that they had "tanked" the apartment. Now the plasterboard has been removed we can see plastic sheeting on the walls and coming up from under the cemented floor. There is evidence that dirt and water has come through at the join between floor and wall. We are told by the company dealing with it that the two parts are not meant to be sealed together. Is this true? If so, how do we ensure water doesn't penetrate into the lounge in future?  Thanks

A We would need to know more details before being able to comment, for example, is the exposed plastic sheeting dimpled or smooth and is it coloured? Is there a sump and pump installed anywhere? Is there any guarantee for the work undertaken? Was it a specialist company or the developer who "tanked" the walls?
A floor/wall detail is potentially one of the weakest points in a below ground water proofing situation but no plastic dry-lining system is designed to withhold a head of water. A correctly installed cavity drainage membrane system should have the floor and wall membranes joined together to prevent odour penetration but, as stated previously, not to withstand a head of water.


Q Thanks for the quick response. The exposed sheeting is white with circular dimples. As far as we are aware there is no sump and pump installed. We don't think the work is guaranteed, it was all done before we moved in. Apparently the builders did the tanking themselves and had it checked over by the council. The builders are denying any responsibility. It would seem there was a head of water behind the sheeting as I can see a water mark about 30cm up from the bottom. Do you think we should invest in a sump
and pump?

A If it is a dimpled sheet type of material then it sounds like the correct material was used but this is only part of it. An installation using this type of material should have perimeter drainage and a sump and pump installed. Such material is not designed to stop water - its function is to control it away to a suitable discharge point i.e. a sump and pump. If it is just fixed to the walls and laid beneath the floor then any moisture that penetrates behind it has no where to go.

When dealing with dampness in such situations all work should be carried out in accordance with BS 8102 - 'Code of Practice for the Protection of Structures Against Water from the Ground'. Although it is not a statutory requirement if an installer has failed to conform to BS 8102 and things go wrong they would have to show why it was not necessary to conform to BS 8102. I am not certain how you stand in view of the fact you are the second owner - you should take legal advice. Did you have a survey undertaken before purchase? Many people are not aware of BS 8102 but it could be argued that your surveyor should be aware and he should have noticed no sump and pump was present.

It sounds like a sump and pump may be your solution but you may also require perimeter drainage which means chunks of the floor up as well. Before you do anything you should take expert advice Which part of the country are you in? We may know someone 'knowledgeable' in your area or may be able to help ourselves.


Is cavity drainage membrane the right option?

Q We have a large, half underground cellar in our late Victorian house. It is very slightly damp, not enough for things to go mouldy but papers left a long time feel a bit damp and cold. There is a small amount of damp (not water) visible in the floor cement after rain. The cellar has lots of windows which are all sealed shut. We were advised to use a membrane method to make the cellar properly habitable but wonder if this is really necessary. Are there any other reliable methods which would be easier (and cheaper) but make the cellar into proper useable living space?
A From what you describe a correctly installed Cavity Drainage Membrane system would almost certainly be the most cost effective system to use. There is also a thermal benefit when using such a system. The alternative is to use a cement based material which would take a huge amount of preparation and result in cold surfaces that you would not be able to puncture and would be prone to condensation and. Anything less such as a builder nailing plastic sheets on the wall would be a bodge.

If you do the job properly then the actual cost relative to the increased value in the property is small. If you attempt to do it on the cheap then you would be wasting your money as you may have to sell one day and the work is likely to be discredited i.e. you might just as well have done nothing. If you have work carried out make certain the contractor complies with BS 8102 as far as practically possible. If he does not know what BS 8102 is get someone else who does.


What is 'Tanking'?

Q Could you please explain in plain English what is meant by 'tanking' in terms of rising damp control? What is the process of tanking? Thanks.

A There is already a question about this on our site that we have copied this below. Tanking and rising damp control are two completely separate things and should not be confused. In general terms tanking is applied to a wall surface to stop penetrating damp for example in a cellar. In an existing structure it does not stop dampness entering a wall - it merely stops it penetrating through to the decorative surface. In a new build situation it should stop moisture entering the wall.


What is meant by 'Tanking'?


'Tank' or 'Tanking' are words often used by the damp-proofing/waterproofing industry when talking about the application of a form of waterproof material directly onto the surface of a wall, floor or ceiling in order to prevent the penetration of moisture. This is usually in a below ground situation.

'Tank' or 'Tanking' are words that should only be used when a complete internal application of a waterproof material is being applied in a given area directly on to all of the walls, all of the floors and if relevant all of the ceilings i.e. at least five sides of a box. In other words it means the creation of a completely waterproof area (a tank) designed to keep water out. Cement based systems are usually used in a true 'tanking' situation. Anything less than a complete application of a waterproof material on to all masonry surfaces in a room is not 'Tanking' in the true sense of the word.

'Tank' or 'Tanking' are words that are very often misused. It is not unusual for a contractors to say 'We will tank that section of wall' whereas what they should be saying is 'We will apply a waterproof material on to that section of wall' - the reason being that they are only coating part of a wall - not a complete system. Some will use the term 'structural waterproofing' which is fine. This may seem rather petty but we are aware of a court case where a contractor lost because of the inappropriate use of the word 'tank'.

Cavity drainage membranes are now widely used to create dry habitable areas in an existing below ground situation. On many occasions we have seen the misuse of the words 'Tank' and 'Tanking' when describing the use of these materials for this type of application. Cavity drainage membranes, when used in this way, are a sophisticated dry lining process. They are neither 'Tanking' nor 'Structural Waterproofing'. Confusing isn't it!


DIY Bitumen tanking - No thank you

Q I am thinking of damp proofing my cellar using the 'tanking' method. I have read that I firstly need to apply a skim coat of mortar to my uneven brick work before applying a Damp Proof Membrane (DPM) in my case, numerous coats of a Bitumen Latex Emulsion. Then before the last, maybe 3rd coat of emulsion has dried I am to throw some clean dry sand (blinding) to provide a key for the layers of mortar... This all sounds pretty simple but, what happens when I want to drill the wall maybe to put up a shelf, or hang a picture with a nail? Am I in danger of piercing the DPM and allowing damp through the holes? How do I get around this? Any information would be greatly appreciated.

A We would not advise using a bitumen material for tanking an existing cellar. We have seen numerous cases where such material has failed as it did not bond sufficiently well and water pressure easily pushed it off. Blinding the last coat with sand does not provide an adequate key either as we have seen cases where plaster is severely crazed and falling off the wall where this technique has been used. Also as you point out it makes subsequent fixing virtually impossible. It is a very 'old fashioned' approach bearing in mind modern materials now available. Most cellars today are converted using Cavity Drainage Membrane which is relatively simple to fix and far less messy than what you propose.


My cellar has started to flood

Q My cellar has started to flood. The water enters around the perimeter of it, and sometimes can be severe, up to 3" of 4". What can I do?
A Ask a cellar conversion specialist to inspect. It sounds like you will need perimeter drainage linked to a sump and a pump.


Damp Victorian cellar

Q I am interested in buying a Victorian semi detached and went to view it. It has a cellar and noticed in there that the back end wall felt damp from bottom to nearly top, all the other walls seemed fine. What is the likely cause of this and its best remedy? Would it be costly? I have heard of CDM and tanking, please advise me on this your assistance shall be much appreciated.

A It is probably true to say that all Victorian cellars are 'damp' so do not panic. What you actually do about it depends upon what you intend to use the area for. It has probably been that way for very many years and provided the area is well ventilated nothing should change. You would only go down the CDM route if you wanted to create a dry area for a specific reason i.e. an extra bedroom or paper type material storage.


Puddles on basement floor

Q When we purchased our 1890's end of terrace 2 years ago, we were told that when there is heavy rainfall a small puddle of water appears in our cellar. We immediately put down a new floor which I believe had silicone in it?!?, we waterproofed the edges with some kind of paint (you can tell I'm a woman can't you) and then laid lino and made it a utility area. However the rain came in and caused a 1" deep puddle. We looked at the drainpipe just outside our house and put some more tarmac around it as a temporary measure, which has so far worked. However last night, the cellar filled with quite a bit of water in two areas. Both puddles were just over 1.5 square metres and about an inch deep. The water is clear and has no smell. I have been downstairs most of the night trying to mop it and have so far filled 4 buckets! I'm just trying to salvage our electrical goods and other personal belongings that are down there. Any ideas? We don't really want to spend a huge amount as we are planning to move within the next 2 years and are a young family.

A There is no cheap way to deal with water penetration into a cellar. It has to be an all or nothing affair i.e. walls and floors. Water will always find its way around or through obstructions that are put in its way unless provision is made to divert it or withstand the pressure it creates. It sounds like the very least you need is a sump and pump probably with perimeter drainage. Have a look at Safeguard Europe, Triton Chemicals, Wykamol web sites. These companies supply sumps, pumps, membranes that would be needed.


They want to do what to your cellar wall!!

Q The back wall of our house is partly below ground (about 1.5 meters).  After a recent flood (a blocked drain, so not necessarily as a result of being underground) we have stripped the plaster off the walls. We are now getting conflicting advice from contractors. One wants to re-inject the chemical DPC (they had used a chemical injection at 100mm intervals vertically and horizontally for the 1.5 meters underground into coursed rubble stonework), put a plastic membrane over the wall and then stud and board (which is the system which we had before the flood and which had worked as far as we can see).  The other wants to 'tank' it. Tanking sounds sensible but what we had before did seem to have done the trick until we had the flood.

A Who ever wants to drill and inject vertically and horizontally below ground does not know what they are doing! Chemically injected DPC systems are not able to withstand hydrostatic pressure which would be present in your situation so it would be a complete waste of time, effort and money. If membrane, stud and board has worked before then go with this but do not allow anyone to drill and inject below ground level. Cement based tanking would also work but it would be more susceptible to condensation and must not be punctured.



Cellar floods after rain

Q We have recently moved into a semi-detached bungalow which has had the cellar converted (plaster boarded walls and tiled floor etc), but when we get a really heavy rainfall there is water penetrating the floor tiles in one corner of the room. The water coming up is clean and disappears the next day. There is also water stain marks on the walls around about 500mm high. Is it possible to rectify this and would the work carried out be guaranteed?
A From what you describe it does not sound like your cellar was waterproofed correctly - What is behind the plasterboard? What precautions have been taken in the floor? In addition to dealing with the walls and floor properly you probably need a drainage system leading to a sump and pump to cater for the periods of rain. Guarantees for this type of work are difficult to come by and there is a huge variation in the competence of contractors who carry out this type of work so be careful. Ten years is regarded as the sensible maximum period of guarantee in such circumstances. If anyone offers you more walk away as they almost certainly do not understand what they are doing.


Water gets into cellar

Q Similar to some of your other questions, I have just bought a 100 year old end terrace house with a cellar. When there is any form of rain, I believe you term it 'free' clear water is collecting. I have to date been emptying up to approx 50 litres out and so don't actually know if the water would drain away naturally when conditions get drier?  I am about to rent the house out and need some form of system (as cheap as possible), which will prevent this problem.  The cellar doesn't have to be liveable as it will just be for storage.  What and who could help sort this.

A It sounds like you need to install a sump and pump which is common in basements so do not be alarmed. The pump has a float activated switch which turns on when the water in the sump reaches a certain level. Perhaps you should also have a drains test carried out as well. Which part of the country are you as we may be able to point you in the right direction.


Water penetrates through steps

Q How can we prevent water ingress through sand stone steps? The steps lead up to the ground floor flat. The occupants of the basement flat have opened up under the steps to use it as storage; unfortunately water is penetrating through the joints on the steps. We applied silicone on the external face (joints) of the steps and underneath the steps on the joints. This has failed.

A To stop water entering in the situation you describe is notoriously difficult. Some have tried applying asphalt over the entire top surface but due to the different thermal properties of the materials used in construction of the steps and the variable stone thicknesses involved cracks will always open up. In addition condensation forming on the stones is often confused with water penetration.
Probably the best long term solution would be to construct a form of 'tent' beneath the stairs using cavity drainage membrane applied to the roof, walls and floor. If necessary the walls and ceiling could then be clad in plasterboard and the floor screeded. Naturally provision must be made for the drainage of any water that penetrates the steps as well as for ventilation.


How should I tackle my basement?

Q Hi I have a 3 story house. The house is built into the side of a hill and is built of granite. The basement of the house has clear water staining (green algae) across 3 sides. Two sides have a sloping green line that marks the contact with soil from the exterior. Ideally I want to convert the basement into two distinct areas a workshop and a laundry room. Any advice as to best way to tackle would be appreciated

A From your description we would suggest that you use Cavity Drainage Membrane on the walls and floor. You may need perimeter drainage and, subject to site conditions, a sump pump. The walls may then be lined with plasterboard and the floor screeded. Pipes and services may be concealed between the plasterboard and membrane and this method is far less prone to the effects of condensation. You should consult a basement conversion specialist whose surveyor(s) are CSSW qualified.
Contact Peter: Email - info@dampdecay.co.uk - Telephone: 015242 71794