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Damp area in ground level bathroom - damp expert stated likely to be caused by lightweight plaster

Hello. We had a new ground floor bathroom fitted back in April and in the last couple of months a damp patch has appeared on an internal brick wall - above the tiles. A damp expert has been round and has confirmed that it is not rising damp and that it is likely to be caused by a lightweight plaster being used and the wall not drying out sufficiently. He recommended removing the plaster and rendering instead. We contacted the company that fitted the bathroom and they advised that render would be too thick (possibly extending over the tiles) and have not had any problems with the plaster before. We have been using a dehumidifier for the past week and this does dry the area out, however the damp patch appears worse again after showering. The bathroom does not have any windows and is at ground level. The other side of the internal brick wall is rendered and does not have any visible issues.
Any advice is much appreciated so many thanks in advance for all your comments.

Thanks David - the pipes are in a different place to the damp patch and its the opposite end of the room to the enclosure/screen. The bathroom installers considered the pipes when they revisited & confirmed its not that.

2 Answers from MyBuilder Plasterers

I am not sure that applying render will solve the problem, in fact it may make things worse as cement based products are not generally permeable, therefore any source of water will be trapped, may be leading to long term damage or appear somewhere else. I note the wall is internal so that should rule out external water penetrating from anything like leaking gutters / downpipe / poor pointing. I also note that the damp patch is worse after showering so I suggest there lies your problem - when the new bathroom was fitted, were there any supply pipes to the shower buried in the wall and if so are they in the area of the damp patch? Is the damp patch adjacent to the end of the shower screen or shower enclosure? If so, check the sealant, if the shower is over the bath do you have full height tiling - I think the solution is more attuned to these issues than plastering alone.

I hope this helps - let me know if you find the source of the problem.



Answered 12th Nov 2013

I agree with david maybe tiles are not sealed correctly wrong sealeant maybe or something else but defo not a plaster problem


Answered 20th Nov 2014

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