Damp in re-skimmed platser on upstairs wall

[Alex Veitch]

Hello

I've just had a small box room re-skimmed in my 1890 mid terrace. The outer wall is showing patches of damp (these are damp to the touch):

wall had been covered in wood panelling, and there was no central heating in the room for the last 6 years, and condensation was evident.

The patches of damp are not underneath a window. The outer wall is rendered and painted, but the render does not appear cracked and thee paint is in good condition. I've tried drying the patches with a heat gun on low power (recommendation of the plasterer) but they are still showing.

I am presuming (following a conversation with the plasterer) that the damp that is present may well be evidence of condensation build up. I am going to get the outer wall painted with damp proof water sealent as a precaution, and would like advice on what to do on the inside. I have seen a paint for inside (Thompson damp seal), but I am not sure if it is a suitable solution - B&Q knew nothing when I asked.

thoughts or advice woudl be appreciated.

Thanks,

Alex

[Andrew Gabriel]

The corner one in particular is very typical of condensation. If this has really soaked into the brickwork, you are just going to have to wait for it to dry out, and it might take many weeks. Keep the room well ventilated until it dries.

OTOH, you don't say how long ago since it was plastered, but this corner area is often the last to dry out in new plasterwork anyway.

If the bricks are wet through, a heat gun isn't going to help much.

Do nothing to it and let it dry naturally. If the bricks are wet through, IME you are talking of ~6 weeks for a single brick wall, and undoubtedly longer for a double brick wall. Any coating you apply is likely to slow down the drying (which runs the risk of leaving permanent damage to your new plaster), and in the case of decorative coats, wrecked by the damp.

If you are considering installing central heating in the room, the damp spots are a good indication where it got coldest and thus potentially good sites for radiators.

[Peter Taylor]

Alex Veitch wrote

You don't say how long since the plastering was done, but it can take quite a while to dry in some situations and the photo's look pretty normal to me. A heat gun won't help much - OK, it will evaporate a patch of moisture locally, but then it will only condense again somewhere else. You need to get rid of the moisture altogether by having plenty of ventilation.

Well, there's a surprise! :o) What are you trying to cure - condensation or penetrating dampness? If condensation then you need to reduce the amount of water vapour you create, warm up the wall surfaces with insulation and increase the ventilation. A coat of damp-seal will do nothing to prevent condensation. If it's penetrating dampness then you need to find out why this is happening. I don't think it's being caused by a missing coat of gunge, so the problem will still be there after you've put it on. (As you can gather, I don't like treating dampness with gunge!). Anyway, it sounds more like condensation to me.

HTH Peter

[N. Thornton]

wrong move

wrong move.

there are lots of causes of damp on old properties: read up on them and go round and investigate. Readers digest DIY manual has a big picture with all of them labelled.

Regards, NT

[Michael Mcneil]

Neither you or the plasterer have identified the source of the water. If it not leaking plumbing it is likely to be a leaking gutter or roof. I am assuming the box roomis near the top of the house and that the leaks are dripping onto the patches outside.

Condensation is an adiabatic process. It will clear up in dry weather if the doors and windows are opened at all. You are never likely to see condensation except in extreme cases where a resident has blocked all draughts and is using an open gas or oil heater. (Note how quickly it clears from a kitchen.)

If the roof is missing slates or they have been repaired then water may be running down the tar paper under the guttering. If there is grass and weed growing in the gutters then the cause may be overflowing -or it may be a tennis ball lodged in the downspout. Are there kids playing locally?

Try playing an hose on the suspected part of the wall outside. There is no cavity but the bricks they used outside used to be solid and pretty impervious. The paint wil throw most of it off anyway.

There may be a crack in the gutters but you would have seen that and it will leave a tell-tale trace quite visible to the naked eye. (It's the first thing surveyors look for and why they carry binoculars.)

Any playing around with a blow lamp is going to cause trouble. Painting is a wasted expense if it turns out to be a simple cleaning job.