Water and Damp in Basements

How to find the source and claim on your Buildings Insurance

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Leaking Basements and flooded Cellars - firstly we need to find the water source - then you can claim on your Building's Insurance.

No Win, No Fee - if we cannot find the leak source of your dampness problem there is no charge. If we succeed then you claim the cost of our Report from your Buildings Insurer.

Click here for our 'NO WIN, NO FEE' Information Sheet.

How to test for leaks - Free Technical Help - 01626 872886 - discuss your building problem with a Qualified Dampness Expert (C.R.D.S.)

Testing to find the water source

A. Ask your local water Supplier to test your Water Mains pipe for leaks. Particularly ask them to test your neighbour's supplies on both sides: if you live on a hill with properties above you check all those on the high side of your house. This service should be free of charge.

B. If you have liquid water in your building (on a solid floor, or in a basement) ask the Water Supplier for an analysis - this will tell you where the water comes from - mains, sewerage or spring/ground water.

C. Test your own drains - test the foul water by finding the man hole cover, lifting it and running a tap to see which hole your water flows from. Block this hole with a rubber bung (available from us - check to see if you have a 4 inch or 6 inch pipe). Then fill up a ground floor sink or loo with water and mark the level. Leave over night, ensuring that no one flushes or uses the sinks, showers or sinks - if not at the same level next day you need a Drains Company with a camera to investigate. Don't forget to remove the bung!

D. Test the surface water drains - place a Dye Bag or granules of drains testing dye (available from us) into the drain and fill up with water. Using a torch, at night, look for signs of the coloured dye - it glows in the dark.

Quick DIY Master Class in Dampness and Condensation - become your own Expert in 1 hour!

Buy our "Dampness in Buildings" reprinted book by the great expert Graham Coleman. A great read, short and to the point.

Click here to buy the reprint.

Survey for Damp yourself

A 'damp meter', surface thermometer and memory hygrometer are useful tools for this diagnosis - if not available, use the back of your hand to assess the relative dampness of one affected area to another unaffected area. (Also see our main Dampness Site www.dampness-info.co.uk )

See our Surveying Shop for more useful tools.

WARNING - the largest cause of repair failure in damp buildings

Replastering old walls - you may only have contaminated plaster and the original source of the moisture may have been successfully tackled (e.g. new damp proof course, water leak solved), but without a 'salt' and moisture resistant sand and cement Render backing your new Plaster will be wrecked in weeks.

Either use this Specification or use our Air Gap Membrane, which you can plaster with a Bonding, lightweight Gypsum plaster

Many, many Builders and Plasterers do not use the approved method of replastering and in most cases the symptoms, of 'salt' contamination, will reappear if they use modern lightweight plasters, like 'bonding' or 'browning'.

Follow this Specification to the letter and watch the Plasterer to ensure that no Washing Up Liquid or Browning Plaster are added to the mix

Replastering Specification - and the thinking behind it.

1. Hack off all old plaster to at least 300mm clear of all signs of damp or salt and at least 1 metre above ground floor level - use a 'damp meter' to test the walls and remove plaster at least 300mm above the highest level that readings can be obtained.

Reason - This is to ensure that the residual 'salts' do not climb above the new plaster in the future.

2. Brush the walls to remove all plaster residue, particularly around angle beads.

Reason - old plaster will have 'salt' in it and will cause damp spots to appear in time. Old Lime or Gypsum plaster residue will react badly with the new sand and cement render, causing 'salting'. Do NOT allow the Plasterer to fix new Angle Beads (at corners) with Plaster of any kind - only use galvanized clout nails or Gripfill type adhesive.

3. Repair any holes or poor joints with sand and cement (4:1) using washed, sharp (means slightly gritty) plastering sand (sometimes called screeding or rendering sand). Do not use fine, unwashed sands.

Reason - fine, unwashed sands often contain salt and the fine particles are too numerous to find enough cement particles to bond together tightly - these two problems make for a weak render, prone to the easy passage of 'salts'.

4. Special Note - walls made with non-porous stone or brick, like granite or blue brick, will require an adhesive to help stick the render coat to the wall - (use BondAcryl concentrate)

Reason - normal renders and plasters stick to the wall by suction - the surfaces need to absorb some water. Without this suction the render or plaster will not grab the wall and may become loose and hollow as it dries.

5. Damp the walls lightly (to reduce 'suction', which can cause excessive drying and cracking) and apply a thin coat (maximum 1/2 inch, 12.5mm) of render consisting of 3 parts sand - dry, washed, sharp (means slightly gritty) plastering sand (sometimes called screeding or rendering sand) with 1 part of fresh (free flowing - no lumps) Portland Cement.

Reason - thick coats are more likely to slump down the wall during application and crack during drying out.

6. Scratch the render surface liberally all over with a nail board, trowel, metal float or similar object.

Reason - without these scratches the natural drying shrinkage will cause cracking, crazing and hollowness to develop - the next coat will probably pull the first coat off as it dries.

7. Use only Renderproof water proofer/plasticiser in the water that the render is mixed with, at the rate of 1 part Renderproof to 40 parts of water. Do not use fine, unwashed or wet sands.

Reasons - Renderproof binds the sand to the cement and prevents liquid water passing through. It also makes the mix stickier (plasticising) which help to hold the render together. Wet sand weighs more than dry, so it will make your mix weak. Fine sands produce a weak, powdery render, which will not resist 'salts'. Do not allow the plasterer to add plaster (usually 'browning') or washing up liquid to the mix.

8. When the render surface is firm enough (but not bone dry, or it will need re-wetting) apply a second coat to exactly the same specification - if further coats will be needed to reach the desired thickness don't forget to scratch liberally. In hot weather spray the render surface with water to slow the drying process.

Reasons - excessive drying out increases the suction and can prevent one coat sticking to another. Rapid drying always increases shrinkage, which gives rise to cracking of the render or finish plaster.

9. Whilst still damp (or re-wet again) apply a skim coat of Multi-Finish or Board Finish. Do not polish or add water.

Reason - polishing the plaster skim finish will produce a shiny, glazed finish which looks good, but is prone to condensation, black mould growth and poor drying.

10.. Delay any decoration for at least one month and then only apply a thin coat of breathable emulsion paint, not a heavy vinyl. Our Replastering Paint is the best option because it breathes and allows the wall to dry out naturally. Do not repaint or wallpaper for at least three months.

Reason - the paint or paper will fall off the wall due to the water vapour that will be trapped underneath in the new render.

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Site written by: David Moore

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