Painting over old plaster

Question

We have just peeled off some old paintwork from our walls.

The wall is dry and the plaster looks in good shape for the most part but it is old and "dusty" - i.e. you can rub your hand over it and it generate dust - unlike new plaster which has a firm shiny finish. I am nervous that if I paint on to this the paint will not key/adhere properly.

What's the correct thing to do? Jut give the wall a good wipe down and then paint with a diluted emulsion for the first coat or fist seal it using PVA?

In my limited experience, painting over a PVA sealed wall is a real pain - the paint does not cover well and it requires more coats.

Any advice gratefully accepted.

A couple of follow up questions: - 1) If I do seal the wall, do I still need to water down the first coat of emulsion (as if I were painting on new plaster)?

2) Is there a difference between PVA sealer (e.g. Unibond) and PVA wood glue . I have 5L of woodglue in the garage that I will never use - could I dilute this down and seal the walls with this?

Answer 1

You do need to seal the plaster otherwise the new paint won't stick as you point out.

My first choice would be to wipe down and then paint with a coat of diluted emulsion as you suggest. You might want to try this on a section of the wall before doing the whole lot to see if you get a good finish.

Dilute PVA will definitely seal the plaster and I can't think of an obvious reason why you shouldn't use the wood glue - but there may be differences in the formulation you need to look out for. How dilute did you make the mixture in the past? I've used a 5:1 water to glue ratio for sealing a ceiling I was going to paper which worked well. Again you could try a higher ratio to see if you can find a mixture that still seals but then accepts paint better.

You might be better off sealing with the dilute PVA then putting up lining paper - which does stick quite well - and then painting that. The benefit here is that the lining paper will smooth out the wall further hiding any remaining imperfections.

Of course the solution that will give you the best finish is to get another skim coat of plaster applied.

Answer 2

My house is 92 yrs old with plaster and lath everywhere. Two years ago we stripped several layers of old, peeling wallpaper. The plaster underneath did the same thing you described, chalking off on our hands, even after wiping everything thoroughly with damp cotton cloths, microfiber, and even tack cloths. We ended up simply wiping down with a damp cloth to remove any remaining paper glue, dust, and dirt, then using 2 coats of a good quality scrubbable interior latex paint. We've had no peeling, bubbling, cracks, or other issues, even in damp, humid areas in the kitchen.

It might be more cost effective to water down the first coat for sealing, but I don't think you'll need to resort to a PVA sealer or anything special, just use a quality interior paint.

Answer 3

1) If I do seal the wall, do I still need to water down the first coat of emulsion (as if I were painting on new plaster)?

No. But I would recommend doing so. Unless you do an amazing "sealer" coat, the first coat of applied emulsion will still suck somewhat into the plaster. I would rather waste a water downed white emulsion coat, than an expensive coat of chosen coloured emulsion.

2) Is there a difference between PVA sealer (e.g. Unibond) and PVA wood glue . I have 5L of woodglue in the garage that I will never use - could I dilute this down and seal the walls with this?

Unless your PVA wood glue had the exact same ingredients (& quantities per volume) as something like UniBond PVA Adhesive & Sealer I wouldn't use it as a "sealer". Why? I honestly can't give you a scientific explanation, but I simply wouldn't want to risk ruining a good paint job by painting on top of a "sealer" that could possibly cause a negative effect on my finished paint job.

Answer 4

I don't work for them (Honest!) but Everbuild Stabilising Solution is f****** great!! It is a polymer sealant which is thinner than water, breathable, penetrating, water-based and dries in 1-2 hours. (Less with a fan or a hair drier...if yer really keen!) Instead of painting/wash-coating a surface made up of multiple components ie plaster, filler, cement, old paint etc. this product, when applied, gives a uniform surface for the subsequent coating to adhere to. Spray on with a pump-up sprayer and brush out. (Wear gloves! It's not toxic but it's a swine to get off skin when it's dried!) Over-brushing produces a light foam that aids absorption into cracks and imperfecions which prevents "suck-out"and reduces shrinkage with fillers(esp.), paper and paint. It's one of my most used products. Try it on a dusty wall. 1 coat seals everything...except lime wash. That takes 3-6 applications but works really well when done. Just a thought. W.