Most frequently asked questions

Damp deception - how to avoid it

Property Repair Systems is OPEN FOR BUSINESS - 01626 872886 - where you can speak to really 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 choosing a Contractor - E: Mail us at

A Damp Proofing Company or a Builder say that I need a Chemical Damp Proof Course - are they correct?

No - not unless they have carried out in depth Site Testing and then sent multiple samples to a qualified Laboratory. Bearing in mind that damp proof courses do not break down, the Company need to prove that the existing DPC has been made ineffective and that the resultant dampness came from Natural ground water. Such situations do exist, but they are very rare.

Does Rising Damp really exist?

Yes, but most dampness diagnosed as 'Rising Damp' is entirely man-made - it is caused by raised ground levels, water leaks from pipes, overflowing gutters, split downpipes - the list goes on. These problems are not solved by installing a chemical or physical (plastic) damp proof course.

I have Damp on the ground floor 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 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 a damp proof course to be 'bridged'

Anything that covers it up which is up against the wall - decking, steps, soil, tarmac - and anything that reduces the drop from the damp proof course from the statutory 150mm (6 inches) to less, which allows rainwater splash up to penetrate above the damp proof course.

How can internal walls get damp

Not from Natural rising damp - only from a water leak. A new chemical damp proof 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

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, pitting, surface roughness 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

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 did not dry out properly

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

I had my walls 'skimmed' with new finish plaster - it now has damp patches again

Skimming over damp or 'salts' will not work for long. Usually the builder or plasterer using Unibond first, as a Primer, which makes the finish look perfect for a while. Salt contamination, or dampness is still present. This needs diagnosis. Complete our Dampness questionnaire.

My 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 below the level of the damp proof course. Talk to us and send us some photos. We can help.

I had Cavity Insulation installed and now I have a damp problem that wasn't there before

This is usually caused by rubbish in the cavities, dirty wall ties, missing patches of insulation (under-filled) or penetrating damp causing the insulation to pick up moisture. Call back the Insulation Installer and ask for an examination of the cavity, or call us.

My Chimney breast walls 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.

The Council raised my pavement - now my walls are damp and my floor is rotten - can I claim from the Council?

Councils are frequently to blame for raising road and pavement levels, breaking the Building Regulations and ruining house walls, floors, skirting boards and plaster. They are rarely pursued for rectification costs.

The underlying problem is the transfer of dissolved 'salts' brought through the walls by a mixture of rainwater splash up (raised exterior ground levels), historic penetrating damp and multiple replastering - plastering adds water each time and reactivates the salts. The salts come from the ground and the building materials themselves.

The only answer is to add a barrier layer against the wall that does not seal the wall (NOT Tanking) - then you can safely replaster using normal Bonding and Finish on your Membrane, which is a total vapour barrier. It does not require lime plaster or sand and cement render.

We recommend Mesh Membrane - this is a BBA tested and Certificated dimpled membrane that creates a small cavity (3mm or 8mm), through which air from the room is allowed to circulate. The air is allowed in via slightly lifted skirting boards (5mm) and air holes into the ceiling void above. The Membrane and plaster should be cut back to clear the floor by at least 20mm, to avoid picking up any residual damp from the wall.

We sell Kits specifically tailored to each job - easy to fix, no waste.

It is vital that you have the new, final surface above the French Drain set to at least 150mm lower than your inside floor level (if solid concrete) to avoid ongoing lateral penetration of dampness from rainwater splash. Ideally have an Aco perimeter drain fitted, tightly sealed to the wall, (use our Structural Pouring Grout) or otherwise lower the gravel surface to give the splash up allowance.

See example of an Aco drain type product here:

Example of perimeter drainage

We can help you by supplying a technical letter to send to your Council to support your claim for repairs.

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.

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

Want Help choosing a Contractor - E: Mail us at

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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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