Preparing walls for redecoration

Leif

Chris25 wrote: »

Do you usually have a rectangular mirror or picture there? Perhaps the back of it has left some residue?

Could it be something flashing through? If it is residue., not damp, then sealer will treat it. I don't know if you need to sand back first, since a residue might mean the emulsion has not stuck to the wall properly, and might peel off in the future. I guess the answer is yes, sand back, then seal, or test the emulsion by scraping some off.

keystone

Yorkie1 wrote: »

OK, if I do decide to go for sealing it at present, is Zinsser 123 the same thing as Zinsser 123 Plus? If not, which one is better for this?

No 123 is a primer/undercoat. 123+ is relatively new (and nearly twice the price) and is also a stain block.

I don't think thats damp tbh. It looks more like old wallpaper paste that hasn't been properly removed. If you don't feel like splashing out on the 123+ or similar a dab of spirit based undercoat will sort it before a fresh coat of emulsion over the whole thing.

Cheers

Yorkie1

Many thanks for your thoughts, all.

gibson123 wrote: »

Leave it overnight, walls never dry evenly. You may find when it dries properly it's not damp at all.

It's been over 48 hours now, and still visible - but thanks for the suggestion anyway.

Chris25 wrote: »

Do you usually have a rectangular mirror or picture there? Perhaps the back of it has left some residue?

The previous owner had a big mirror against the wall; she moved out 2 1/2 years ago and I've had a much smaller picture there since then. It doesn't cover all the 'damp' and there was no sign of the 'damp' until I painted over the original paint.

Leif wrote: »

Could it be something flashing through? If it is residue., not damp, then sealer will treat it. I don't know if you need to sand back first, since a residue might mean the emulsion has not stuck to the wall properly, and might peel off in the future. I guess the answer is yes, sand back, then seal, or test the emulsion by scraping some off.

Hmm. The previous owner had the whole house skimmed and painted throughout (that's another story - the skim is poor quality and I don't think a mist coat was used :mad: ). I've had problems with the paint lifting elsewhere in small areas when overpainted, and with the skim falling off, but absolutely no similar signs of 'damp' elsewhere in the house so I think that's probably unlikely.

Could try the scrape test, though.

keystone wrote: »

No 123 is a primer/undercoat. 123+ is relatively new (and nearly twice the price) and is also a stain block.

I don't think thats damp tbh. It looks more like old wallpaper paste that hasn't been properly removed. If you don't feel like splashing out on the 123+ or similar a dab of spirit based undercoat will sort it before a fresh coat of emulsion over the whole thing.

Cheers

Definitely won't be old wallpaper paste given the history of the wall.

I'm being really dense now, I'm afraid. What actually is a spirit based undercoat, and won't it mean that the emulsion fails to stick to it (like emulsion over gloss)?

I've rung my builder to ask him to come and have a look, in case it is a ventilation issue, but assuming he's OK then there's a range of possible things to apply to block whatever is causing the stain. Spray-on stain sealer, Zinsser 123, Zinsser 123+, or spirit based undercoat. Which would be most advisable, do you think?