is mist coat still necessary on 3 year old bare plaster?

[Yeeyeelovesraaraa]

Just that really. Had walls plastered 3 years ago, had baby, only just getting round to painting it now!

I know you need to put a mist coat on fresh plaster - but what about 3 year old plaster? Don't want to cut corners but don't want to waste time if unnecessary!

Also if I do what ratio of paint to water would you advise?

[SwedishEdith]

I did in same circumstances. It's a pain as it dribbles everywhere but dries quickly.

[PigletJohn]

if the plaster has never been painted before, yes.

you want the paint thin as milk.

maybe 20% water

it will sink into the plaster and practically disappear, and be instantly dry. This is correct. You will know you have sealed the plaster when it no longer sucks the moisture out of your brush. I usually apply two mist coats, or until the pail I have mixed up is all gone.

you have to stir the tin very very thoroughly before ladelling out enough for your mist coat, and then again after adding the water. you can get mixing tools that go in an electric drill to save time and effort.

apply it with a brush not a roller. Synthetic bristles (often white) are better with water paints because they don't go floppy like natural bristles (usually black) in water.

If somebody has put glue on the wall it will prevent the paint touching the plaster. Try and get it off by wetting and using a broad metal scraper. It will come off like sludge.

You can use a white matt emulsion for your mist coat, it will be cheaper than your fancy finish paint.

[WhichJob]

How long should fresh plaster be left before a mist coat is done? Does anyone know? We are getting our ceilings and walls done soon so it would be good to know.

[PigletJohn]

until it's dry.

modern gyspum plaster is dark coloured, sometimes shiny brown, when it goes on, and dries to a matt pink. Sometimes, e.g. if there is a thick bit over a hole, or a wet brick, or damp due to a leak, the brown patches linger on for a week or more. You can't paint them as the paint will not dry.

you will easily see the difference.

Ceilings dry in next to no time.

Houses dry by fresh air, not heat, so open the windows and the loft hatch.

If the walls themselves are damp, which is common on a newly built house where the walls were exposed to rain before the roof went on, use a porous, breathing, non-vinyl matt paint. Dulux Trade Supermatt is best-known. Other paint makers may offer one, but examine the label or contact the manufacturer to confirm. You can order colours to be mixed, but white and magnolia are off-the-shelf and cheapest.

It is not very durable and will not withstand scrubbing, but makes the house look decent and you can paint over it once the wall is dry. Takes six months to a year. All the time the walls are drying, you will get condensation mist on your windows in the morning.

[PigletJohn]

gypsum

[WhichJob]

Thanks Piglet, that's great. Do you mean the walls could take six months to dry before we should paint mist and paint them? We are in an eighties style house just getting rid of artex and smoothing out the walls so the walls haven't been rained on.

[PigletJohn]

a week probably, maybe two. Your walls should be as dry as dust. Watch them change colour as they dry. Where you have added new sockets or bricked up a fireplace, the new plaster will be deeper so will take longer than on the skim. Ceilings will be dry in a day.

You are remembering to rewire before plastering, aren't you?

[Yeeyeelovesraaraa]

thanks piglet john.

why do you say use a brush & not a roller?

its hall stairs & landing x 2 (3 storey house) so waaay too much surface area & too hard to reach for brushing - was planning to use my long arm roller even though it shall shower me in white spray!

[PigletJohn]

because it will drip and splash, being so thin.

[Soslowmo]

whichJob we did the mist coat as soon as the walls were all dry - we used an Industrial dehumidifier and it only took a few days. I think we had the room plastered, dried and fully painted within a week, but it was tough going!

[WhichJob]

Thanks soslowmo. I don't think we have any energy for more DIY this week and no dehumidifier here but it is good to know it can dry that quickly! I didn't even know about a mist coat until I saw this thread, but the plasterers will probably tell us about it when they finish.