UKH

I thought I would turn to the UKC knowledge database for some advice on how to deal with a damp patch after repairing the roof and (hopefully) stopping the leak.

The wall is taking a long time to dry out but appears to be getting there. I am thinking of removing loose plaster and getting down to something pretty solid. Then painting with some PVC glue-type sealant. Then using a thin skimming layer of plaster to smooth off above this before painting. 

Is it worth renting/buying a dehumidifier to help in the drying out process?

Any other tips?

Advice appreciated

Alan

I would remove the plaster, keep any windows open and try to forget it for a couple of months.

Dont PVA it until fully dry.

Looks like lime plaster, how old is your house?  We've been in a stone built Victorian house for 3 years, and have put a lot of work into restoring breathability to the walls.  The upshot of this has been a big reduction in damp problems.  If this applies at your house, steer clear of the PVA and gypsum based plaster and patch with appropriate lime products, then paint with breathable paint.

If none of that is relevant, your approach sounds ok but you may need to deal with salts that have come out of the plaster, I'm sure someone better informed than me will be along shortly to expand on how to do this.

Rule of thumb is a month per inch thickness of wall. Mine took 24 months to dry. A dehumidifier will help but I would leave it as long as possible before any redecorating.

That does look like an old lime wall designed to breathe, so PVA as a rule would be counterproductive, the more ways that moisture can get out the less likely it is to get trapped or end up elsewhere 

Ancient (1840) however not the plaster on this chimney breast. My daughter is currently removing the wallpaper and it is now obvious since I posted that this is a previous repair with modern red/brown plaster and ancient stuff lower down on the wall. The damage is all on the red/brown stuff.

Alan

Ha, it is our bedroom so easier said than ignored when it is the first thing I see in the morning. Mind you the damp patch has been nagging at me for over a year now anyway.

Alan

ah I can see the picture better now on a PC rather than a phone. 

looks like an old lime wall, previously patched with modern gypsum plaster and then wallpapered and gloss painted ? The wallpaper and paint will provide a waterproof skin keeping any moisture inside the wall or moving it to where it can get out. looks like the wall below the gypsum is leeching salts where the moisture if being forced out there as that is the only way past the waterproof plaster and wallpaper combination. 

I would be removing all of that paper and seeing what happens - you might be able to watch the wall visibly dry - ours did. Personally I would pull off the modern plaster too which may have the consistency of cheese - let it dry and then re-skim in lime and paint with a breathable paint like clay paint. 

Or stick a piece of plasterboard over it, cover up the problem and make it a problem somewhere or to someone else. I don't recommend this, but many do.

Now we have full view having stripped all the paper, it is obvious that this is a modern repair that was either covering up an existing problem, or the problem has come back. The ancient lime plaster is on the lower section and is mostly fine, a little flaky but nothing we can't deal with. The modern gypsum plaster is the repaired section. The wall had thick backing paper but wasn't gloss painted. However, it has visibly dried overnight now the paper has been removed.

Thanks for the advice.

Alan

If you want to do a 'proper job' strip the whole chimney breast, leave it a year or so to dry out and confirm you did actually fix the leak properly, re-plaster with Lime plaster (pay an expert) and paint with breathable paint - we use Keim Optil and it works well.  Trying to match a plaster patch is very difficult, and as it's a chimney breast it's a relatively small 'whole wall' to re-plaster.  If the whole house is tatty enough to not warrant a proper job then a lime plaster patch repair and re-paint with Optil is the way forward. Get yourself a moisture meter (Protimeter, about £80) and see what's damp and where, and track the drying out process. If you're nowhere near the sea you won't have much salt from sea air trapped in the wall to inflate readings, but you may have salts from soot. The moisture meter will be useful for keeping tabs on woodwork that's likely to suffer rot elsewhere in the house. It will likely take months to dry out. Keim Optil is good because it lets salts through without blistering, and can be sanded (unlike emulsion).  Any efflorescence can simply be brushed off, and if the paint eventually breaks up and comes off due to continual efflorescence you can easily touch it up.  Don't put emulsion on it as any dampness will cause it to blister.