Basements and cellars
Does a waterproofing guarantee in a drawer mean the basement walls are dry today?
No. The certificate records a system someone installed, on the terms written on it, while dry, damp or hidden is what the walls are today, and only where the survey could see them. A guarantee is not the same observation as a dry wall on the day of the inspection. Read the paper for what it claims, and do not let it replace the stains.
Last reviewed 24 October 2026. Written for buyers in England and Wales unless this answer says otherwise. No named surveyor has signed this page. It is general guidance, not a report on your house, and not legal advice.
What is the fuller explanation?
Tanking and membranes hide the masonry. A surveyor who was not there when they went on cannot see behind them, and a certificate does not give that view. Salts, bubbling at the edge and a tide above the lining are today’s clues. The Property Care Association’s approach is to understand the moisture rather than to trust a product slogan. Government damp guidance likewise starts with the cause, not with a folder.
Ask the seller for the specification as well as the cover note, and ask your solicitor what the small print actually promises. The survey should say whether it saw the certificate or only the coating. A missing page is a paper gap. A wet wall is a building fact. Do not average them. There is no reason to sand the coating off before exchange to check the story.
What should you ask your surveyor?
- Did you see the certificate, or only a coating?
- What do the walls show today, above and beside the system?
- Are you treating the paper as proof the walls are dry?
What are the typical next steps?
- Read the guarantee for the areas and the failures it actually names.
- Believe the damp you can see today over a slogan in the drawer.
- Do not strip the system before exchange.
Costs vary with the building and with who you instruct. Where this page does not cite a published figure, ask the surveyor, a relevant specialist, or your solicitor for a written quote. Do not treat a forum average as the price.
Also asked about this
Is an old chemical-injection guarantee the same document?
No. That paper is about a wall treatment upstairs or at the base. A basement waterproofing certificate is a different system. Neither proves the basement is dry today.
Does a dry day cancel a stain?
No. A stain is still evidence of past or present water. The certificate does not wipe it.