Dealing with small damp areas on plaster

[MisterBoy]

I have several isolated damp spots on plastered walls/ceilings - typically up to a foot in size - which are typically linked to historic water e.g. a slipped roof slate.
The problem is that once it has got damp, it just keeps sucking in water from the air, etc, and I cannot tell which may still have an underlying issue. I've got peeling paint, a bit of ceiling that has mildew, etc.

And I think even uf the original issue is fixed, a damp spot in plaster can spread?
Should I be ruthless and cut any such area back to bare brick rather than faff about with stain/damp blocking paint? Or will treating such areas with the right product mean they can dry out - provided there is no damp behind the plaster?

And then how do you fix an area of this sort of size? If you rip plaster off a brick wall that can be quite deep, presumably not really appropriate for home-fixing, and really needs plastering? Or is there something a DIY-er can do that's in-between a polyfilla bodge and proper plaster+skim coat?

 

[Wayners]

Open window and put a summer fan on to move the air.
That will speed up drying.

Next is a dehumidifier. If you live in a house with high moisture then you should really have a dehumidifier going every day this time of year to keep on top of things.

Also start looking at why you have high moisture and is there anything you can do to reduce it.

 

[JohnD]

How long has it been damp?

If it hasn't dried out after a year, then the ventilation of your house is less than necessary for the water being added.

Whether there is insufficient ventilation, or excessive water being added, e,g. from clothes being dried indoors, or steamy showers without a powerful extractor fan, or leaks, I can't see from here.

Are these damp patches in a bathroom? Kitchen? Bedroom?

Some photos will help.

A damp patch will not get bigger unless more water is added.

 

[MisterBoy]

The worst one is in a bathroom - there is a DMEV but the room is used every day for bath/shower and struggles with condensation (solid brick wall) so the wall WILL be wet. My understanding is once plaster has got wet and the paint failed, it is VERY susceptible to moisture getting sucked back in. There was historically a leak in the roof but this was addressed so I'm not sure if I can treat & over-paint successfully. It isn't feasible to not use this bathroom for days/weeks and dry the damp patch out, sadly.

 

[JohnD]

The worst one is in a bathroom - there is a DMEV but the room is used every day for bath/shower and struggles with condensation (solid brick wall) so the wall WILL be wet.

So increase the ventilation.

Next time you tile it rip off the plaster and use an insulated backing board.