Painting directly onto plaster

[burton]

I’ve just bought some Wickes Vinyl Matt paint (beech hut blue) and have begun “cutting in” but the paint looks translucent and you can see the plaster beneath it. Should I apply an undercoat first? What sort of paint to I need to use for an undercoat?

Thank you learned friends.

[jaz]

Water down some white emulsion (about 50%) and put a mist coat on or it will all fall off.

you will need 2-3 coats of your blue colour afterwards

[burton]

What’s a mist coat? Do you still apply with a brush?

[jaz]

Just watered down paint that seeps into all the holes and forms a good bond with the surface. Some people add a little PVA glue as well as water down paint but it’s not really required.

Can be applied with a brush or a roller, but it’s messy as it’s really watery

[FUZZY]

No to PVA. It’s an old wives tale.

A cheap matt emulsion is your best bet.

[oldfogie]

No PVA. Don’t use vinyl matt for the mist coat, use contract matt. Get snots off with sandpaper first. You can get sander that goes on a pole if you have other rooms to do. Caulk after the mist coat (use non-cracking).

[dave]

You should first go all over the plaster and give it a light sanding.
Mist coat and cut round the edges

light sanding

first proper coat.

light sanding

possibly last coat.

How do I know. My daughters fiancee has who has just fully painted our house did it this way on new plaster and the finish is awesome.

I asked if all the sanding was nesecarry and he said only if you want a proper finished job.

[burton]

Thanks, looks like I’ll have to head back out to Wickes for some sandpaper and white emulsion!

[keith]

Assuming this is new plaster you are painting? If so, then, as suggested by others, a light sand and a mist coat is the the thing.

A light sanding is all you should need: if it’s new (decent) plaster the surface should be flat and fairly smooth so it should just need any knibs removing, then sanding to provide a key if the plasterer polished it a bit too much. You just want to remove any shine,no need to go overboard. Just ‘float’ the sanding block over the wall and you should feel any imperfections. Ideally, try to look along the wall with a window/light-source at the other end and you will see any knibs or other imperfections.

It doesn’t sound as if doing this would make much difference but, as bedspring said, it really makes it look smart – assuming your painting is up to scratch, obvs.

Tip for the mist coat: dilute about 1:1 but ensure you give it a really thorough stir, ideally use an electric paint whisk, otherwise you’ll end up with water on some of the wall and thicker paint on the rest. The mist coat should look fairly even and well-covered.

[pakpak]

Ive never heard of needing to sand fresh plaster, the finish should be such that it is free of imperfections….i served my time trowelling the stuff onto the wall.

Priming the wall with a watered down emulsion will suffice but again not strictly necessary, a decorator told me not all emulsions are created equal, with trade paints formulated differently for just this purpose.

Ive just re-skimmed my loft conversion, no priming, just deluxe trade paint straight onto the plaster.

[keith]

It’s more a case of lightly going over any well-polished patches to provide a better key, no need to sand the whole wall (unless it’s all been highly polished). Removing any knibs, bits that have been left on corner beads etc is just fine-tuning; it wouldn’t stand out if it was left but it makes the job that tiny bit smarter. You’d never see guys on the sites doing any of this, it’s only something you’d maybe take the time to do on your own house, or see a really high-class painter doing.

I’ve heard some paints can now be applied without a need for a mist-coat but some still definitely do need one and mention it in the MI’s.

[Sammyf]

What are people’s opinions on undercoats versus overcoats? I’ve found that when glossing it’s better to do enough undercoats to give a uniform surface colour before a single coat of gloss, rather than a single coat of undercoat and multiple coats of gloss.

[keith]

Gloss doesn’t cover. You’re doing it the right way.