Damp wall on the first floor

Cracks in render can cause damp walls upstairs.

I was in a end of terrace house in Cardiff last week and came across one of the dampest first floor wall I have seen. The Home Buyers survey did not pick up the level of damp (as most surveyors only really look for damp downstairs), but my damp meter was hitting over 25% water content regularly.

On inspection it was the usual suspect of cracked render on the gable end wall. The wall was cement rendered and there were some obvious cracking. With the wall facing east one might have expected less ingress, but the damp had come right through the solid wall and was appearing on almost all areas of two bedrooms’ walls.

It is worth noting that most of this type of damp is trapped in the wall by the small hairline cracks. Large missing render will let in damp, but at least some of this can then evaporate off again, but small cracks don’t let the evaporation happen. So look out for damp in cement rendered walls. It will be there somewhere and you might need a damp meter to find it. People go out of their way to cover up damp and so it can be done quite effectively over the short term, but it will show over a period of time. The other more permanent damp masking technique is dry lining, so always tap the external walls to see if they sound hollow.

With wet walls being around 38% less efficient than dry ones, I really hope that the customer takes the advice has replaces the cement with a lime putty stone dust aggregate render. This will be a great energy efficiency measure as well as being the healthy option and the correct one for the long term future of the structure.