Cellar or Basement Damp

How to avoid costly work

Property Repair Systems is OPEN FOR BUSINESS - 01626 872886 - where you can speak to real damp people

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Do any of the questions or bogus statements below affect you and your building? Contact us if you need help with damp - 01626 872886 .

If you'd like to send us the details of your problem complete our Dampness questionnaire.

Want Help - E: Mail us at help@propertyrepairsystems.co.uk

Cellar or basement damp

Why is this different to above ground situations

Below ground, the deeper you go, the pressure of the water pressing on walls steadily increases. This is called Hydrostatic Pressure. It is sometimes referred to as a 'head' of water.

This pressure forces water through walls and floors underground, even where damp proof membranes have been installed, because perfection, particularly at joints, is hard to achieve, even in new buildings.

What tests should be done before waterproofing

Most buildings were dry when originally completed. Many buildings have been dry for years and were certainly dry when they were built. This means that for underground damp to gradually or suddenly appear something has changed. That 'something' is usually man-made - failure of mains water supply pipework, surface water and foul water drains being the most common. Central heating pipes and other internal plumbing can also contribute.

Not all faults occur in the property concerned - sometimes the faulty pipework lies next door, in the path or road or under the garden.

So it is vital to eliminate these causes BEFORE spending money waterproofing a cellar or basement. If you carry on regardless the waterproofing may fail or will simply divert the water, forcing it to climb further. It will not disappear on its own.

Water Leak Tests

1. If you have a Water Meter carry out a basic test first - with everything turned off in your house (do not then flush any toilets) does the Meter indicate any consumption over a 6 hour period? Check the readings very carefully before and after - the amount will be very small.

2. Request a Mains Water Test from your Water Supplier. If you have any liquid water in the cellar or basement ask them to also take a sample and confirm whether the water contains mains water, foul water or ground water. A foul water drains leak will not usually smell - it is too well filtered through the soil.

3. Order a drainage pipe expanding bung from us and test your foul water pipes by blocking the outlet - you will need to lift the man hole cover and flush a toilet to check which pipe to block. Once the bung is in place fill up a ground floor toilet to the underside of the rim. Check the bung for leaks. Leave for 6 hours and check the level in the toilet - it should not have moved.

4. Order some surface water drains testing Dye from us, one colour for each drain. Fill the drain with water and add the Dye. It is harmless to the enviroment. After 2 to 3 weeks the colour(s) may appear in the cellar or basement.

5. If you suspect a Central Heating leak ask your plumber to pressure test the suspect pipework.

Want Help - E: Mail us at help@propertyrepairsystems.co.uk

A Damp Proofing Company or a Builder say that I need my Cellar 'Tanked' - are they correct?

No - not unless they have carried out in depth Site Testing and then sent multiple samples to a qualified Laboratory to prove that the current dampness came from Natural ground water. Such situations do exist, but they are very rare. The majority of cellars and basements have been dry for most of their existence - ingress of moisture is usually caused by some kind of adjacent water leak, not related to the age of the building. Tanking just forces that water to exit higher up the wall, or spread out. Tanking with liquid products onto damp walls does not usually work - the tanking product is diluted and damaged by surface 'salts', which results in patches that never dry out properly.

Cellars and Basements always leak at some time?

Yes, but most dampness diagnosed as 'Rising Damp' or Penetrating Damp is entirely man-made - it is caused by water leaks from drains, pipes, overflowing gutters, split downpipes - the list goes on. These problems are not solved by applying liquid Tanking products

I have Damp on the floor of my Basement and I want to know why

Complete our Damp Questionnaire and we will diagnose the fault. Photographs of the walls, indoors and outside are also useful. If sending photos please limit each E Mail to 10mb of Attachments - our Letterbox is limited to 10mb.

I had a chemical Damp Proof Course installed in my Cellar but the damp problem is back again

This is not surprising - it means that the original cause of the dampness was not found, merely covered up. Complete our Damp Questionnaire and we'll help you to find the underlying cause. Then we can give you a cure.

What causes damp proofing to fail in a Basement

Water leaks under, around or next door to your basement. These usually come from broken drains, leaking mains water supply pipes and surface water gulleys. Once the problem has been found and fixed the basement will dry out.

How can internal Basement walls get damp

Not from Natural rising damp - only from a water leak. A new chemical damp roof course will not solve damp problems on an internal wall (both sides indoors), even with replastering using a 'waterproof' render, or 'Tanking'.

Do I really need to take off the plaster in my damp Basement

If it is damaged - yes - but if there is no damage it may dry out with some help. Damage includes roughness, delamination causing the skim finish to fall off, pock marking and blistering. Drying out can be assisted using a Dehumidifier (close all doors, vents and windows to the affected room).

May I skim over existing plaster in my Cellar

The Builder's favorite fix - Unibond and Skim! It only works if the walls are not contaminated with 'salts' - and these cannot be seen with the naked eye and the walls are dry. Otherwise don't risk it - ask us first.

My Replastered wall in my Basement did not dry out properly

Salt contamination or dampness are still present. This needs diagnosis. Complete our Dampness questionnaire.

My Cellar wall was Tanked, but damp patches are back

Tanking products may not dry properly if used over damp walls or salt contaminated walls. Tanking should only be applied to dry, salt free walls. Talk to us and send us some photos. We can help.

My Chimney breast walls in my Basement are damp in patches

Usually caused by 'salts', acids, resin and condensation coming from the chimney flue - it slowly passes through the walls and eventually reaches the plaster. Only cured by removing the plaster and fitting our Mesh Membrane - then you can replaster with complete reliability.

Want Help - E: Mail us at help@propertyrepairsystems.co.uk

Case Studies for Membrane Linings

Basement Conversion - click here

Convert a Basement - click here

Property Care Association

We are long term members of the PCA - The Property Care Association - the professional body for the Damp Proofing industry and our Dampness Surveyors have over 50 years of experience between them.

If you prefer to use a Contractor, rather than our free advice service, then go to the PCA Website where you can find the nearest qualified specialist companies. They should give you the same information that we provide. If in doubt E Mail their Reports to us for checking, before spending any money.

Link for the PCA - click here.

To give us your details for help - Dampness questionnaire.

Want Help choosing a Contractor - E: Mail us at help@propertyrepairsystems.co.uk

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Site written by: David Moore

David Moore, B.A. (Hons.), C.T.I.S., C.R.D.S. Technical Author


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