Wet/Mist Coat on walls plasterd a year ago.

[asimon]

It might be a bit late in the day to ask this, but here goes, I had my walls and ceiling plastered/skimmed a year ago now after completing some renovations, looking at the forums, I opted for putting on a Wet/mist coat, have just finished doing the walls, which took a long time, not just because of the area, but mainly because I was doing this on and off, for the past 8 months, doing the walls was messy enough (I'm not really a DIY, but do try to do a much as I can by myself, but I must confess it takes me some time). To get to the point now is it still worth while doing a wet/mist coat for the ceiling

 

[Pford75]

I assume that your newly plastered walls are gypsum plaster (the pink stuff) rather than lime? If that is the case, then the rationale for a mist coat is that bare plaster will 'suck up' any paint that is applied. Therefore, a watered down coat of trade emulsion is both cost effective and should provide a decent base for later coats of your chosen paint.

If the plaster is lime, then one of it's most useful properties is that it is breathable. Covering it with non-breathable emulsion is missing the point of lime plaster slightly and you might want to consider limewash, distemper or other similar breathable coverings.

 

[MdB]

In my house, virtually none of the paint has stuck properly to the plaster and just flakes off. My guess is that this was due to the first coat not being watered down. I'm told it is due to the paint flash drying when it comes into contact with the very absorbant fresh plaster and doesn't make a proper bond.

 

[AMc]

Again assuming this is pink gypsum you can get a decent finish by lightly wetting the wall, waiting 5 minutes then applying a coat of trade emulsion. I half filled a roller tray with clean cold water and used a brand new roller to apply it. In most rooms I applied a flash of water one coat of trade emulsion and 2 coats of proper coloured paint. This worked well for me as a base for more expensive Little Greene and Craig & Rose top coats on walls.

Big tubs of trade emulsion are available at very low prices compared to 'posh' paint. I used Travis Perkins own which worked out OK. Check the price and how much you need I bought 20 litres for about £2 more than 10 ?!?

Two coats of undiluted contract emulsion have done the job on my older ceilings. I think the builders used one watered down then one full strength coat on the new plaster but I'm not sure. On ceilings I would water down trade emulsion in a big tub/bucket so you have a consistent thickness overall then apply a top coat and decide if you need a final coat

I did ceilings first then walls so watch out for roller splash from the ceiling on your new paint! A roller on a pole will make the whole job much faster.

 

[asimon]

Thanks everyone for your replies, I will forge ahead with doing the wet coat on the ceiling

 

[BMcD]

Hi asimon

I notice you're in South East London, in which case gypsum plaster may well be grey rather than pink. Also, it will be worth washing down bare plaster, especialy when its be bare for a long time, with sugar soap or something like that to get all the dust out of the pores and allow the paint to soak in.

 

[chuckey]

I am concerned with AMc's suggestion. My reason is that if the pores in the new plaster are filled with water, then the full strength coat can only settle on to the water. Using a dilute coat first would mean that as the dilute coat fills the plaster's pores it carries the particles of paint with it which will dry out leaving a thin coat of the hardened paint within the pores linked to the hardened paint on the surface. But it is better then a coat of hardened paint just sticking to the plaster's surface, I guess.
Frank
FWIW I have tried Dulux's plaster primer, would not recommend it at all, I use diluted emulsion.

 

[Michelle73]

I've had a few walls skimmed with the pink stuff and each time I prime them with a mixture of PVA glue and water before applying normal emulsion.
Extremely cheap, easy to apply and dries very, very fast.

 

[AMc]

I am concerned with AMc's suggestion. My reason is that if the pores in the new plaster are filled with water, then the full strength coat can only settle on to the water. Using a dilute coat first would mean that as the dilute coat fills the plaster's pores it carries the particles of paint with it which will dry out leaving a thin coat of the hardened paint within the pores linked to the hardened paint on the surface. But it is better then a coat of hardened paint just sticking to the plaster's surface, I guess.
Frank

Not sure I fully understand that, what I read indicated you wet the walls then allow them to dry for 5-10 minutes before you begin with the full strength trade emulsion. My understanding was this prevented the dry plaster from sucking the moisture from the emulsion before it began to cure but I claim no significant expertise in paint chemistry. The major appeal to me was I didn't have to premix a lot of dilute emulsion.
I applied one trade then two top coats & I've had no problems with adhesion, but the plaster had been drying for several weeks over summer so it may have been unnecessary and I'm more than happy to bow to greater experience!

 

[Toby Newell]

Hi

My family has been in the finishing trade for over 100 years and my apprentice is an accomplished painter. It's simple, for pink gypsum skim (final coat) plaster thin out the first coat with 10 to 20% water simple. No other options apply. For lime plaster I am afraid I would have to defer as I do not have any knowledge of this.

Toby

 

[tom.harrigan]

Painting on fresh plaster is a lot of work. I know, I watched my wife do it!

1. Very watered down mist coat (up to 50%)
2. Watered down mist coat (about 30%)
3. Slightly watered down coat (10-20%)
4. Final coat (~10% water)

Follow that and you will have a good finish and no problems.

I hate painting, so I use Earthborn paints whenever I can. They just need one watered down coat plus one full coat.

If you don't do a couple of mist coats, your paint will flake off. Professionals seem to always water down paint a little - it makes it easier to apply.

 

[lou]

Tom - is that for painting fresh lime plaster?

 

[tom.harrigan]

I used claypaint on the lime plaster. If I were to paint lime with modern paint, I would treat it exactly like gypsum - ie. lots of watery coats.

Lots of watery coats always works, for any paint (well not gloss - obviously) on any surface. However, if you have gone to all the effort of putting lime on your ceiling or walls, I would definitely not use acrylic paint (well I might in a small bathroom).

 

[Schoolmarm]

Why would you want it covered in acrylic in a bathroom? I thought that the great thing about lime and limewash was it's ability to absorb and hold moisture, releasing it later.

Acrylic paint would allow moisture to sit on it and go mouldy. My current disgusting bathroom is a perfect demonstration of this.