Painting new plaster - any tips?

RainbowsInTheSpray

Three months ago we had a stretch of stud walling installed and as a result there is now an area of plaster which needs painting. We haven't been able to decorate until now.

Please note we are NOT talking fresh plaster. It is completely dry. Can we use a thinned paint to act as a first coat for this... or would some other tactic/method be appropriate? Any thoughts very welcome.

koalakoala

Yes, a thinned coat first, then a couple of coats

TELLIT01

I've often read about using a thinned paint coat first, what is the reason for that?  I ask because I've had two emulsion jobs done, by the same person, and they have not done that.  Just 2 coats of emulsion and the finish is perfectly OK.

Bendy_House

Yes. It's called a 'mist' coat.

Clean the plaster first - wipe down with a damp cloth to make sure there aren't any dusty patches.

Any shiny polished areas? Sometimes plaster can be over-trowelled ('polished'), and that gives it a very hard skin which paint can find it hard to adhere to. You'll recognise them by, yes, being hard and shiny, and also often a deeper pink, and not the nice dusky shade. A light going over using ~180 grit will sort it. 

Look at the finish at a low angle, too, and use her fingers to feel for bumps and ridges - again, a light going-over should sort it.

liberty_lily

TELLIT01 said:

I've often read about using a thinned paint coat first, what is the reason for that?  I ask because I've had two emulsion jobs done, by the same person, and they have not done that.  Just 2 coats of emulsion and the finish is perfectly OK.

Was this onto new plaster though?

Always apply a mist coat is the advice I was given years ago.

The apology for builders/decorators employed by the previous owners of our current house obviously painted straight onto the bare plaster in the extension they put up. I'm sure it looked fine for a while, but when we came to decorate the space, the paint had bubbled and peeled in vast swathes.

Rubbing it down and filling failed to improve the situation so we've ended up re-plasterboarding and skimming the lot (fortunately DH is excellent at plastering!) Then it will be mist coated ahead of applying our chosen coats of emulsion. 

Bendy_House

TELLIT01 said:

I've often read about using a thinned paint coat first, what is the reason for that?  I ask because I've had two emulsion jobs done, by the same person, and they have not done that.  Just 2 coats of emulsion and the finish is perfectly OK.

The thinned paint just penetrates slightly into the plaster surface, and helps to adhere it on.

Without, there's a risk of the paint sitting on the surface and barely holding. Lots of cases where applying subsequent coats have seen the base coat peeling off in sheets and wrapping around the roller...
It will come down to how porous the plaster is - if it's at all 'polished', neat paint will really struggle to stick.

stuart45

Plaster sucks the moisture out of the paint, so it won't cure properly and adhere to the surface. By adding water it stops this happening. 
It's best to leave the mist coat for a day, and check it with a bit of masking tape. If none comes off with it the mist coat is fine. 
You can always do a second most coat.

RainbowsInTheSpray

Thank you for the comments. So, assuming that this thinned or 'mist' coat is required, what ratio of neat paint : water should be used?

stuart45

Painters can't seem to agree on a set ratio. Some say 75% paint, others 50%. It probably depends on how thick the paint is. 
Yes, mix with water.

baser999

Had my ceiling re plastered a week ago and lef5 to dry. Have today applied two coats, full strength, Dulux Supermatt emulsion, dried perfectly well, very pleased with final result. Brother had similar with his few weeks ago, no problems.

malexicon

Hi there. I will be in a similar boat to you and am yet to paint but my plaster mentioned that screwfix sell a special ‘no nonsense fresh plaster paint’ which seems to get good reviews. I am tempted to try this for two coats then a third one of soft Sheen bathroom paint to finish off. 

As I said - not a rec, just another option as some folk say a mist coat can be messy and watery to work with.