Patchy mist coat?

[Mat1980]

I'm having a bit of an issue. Plasterer said no need to sand first but we've just put on our first mist coat (well plaster paint) and there are loads of odd looking patches.

Will we have a big problem going forward or is it just a case of sanding between coats until they are gone?

Any idea what they are from?

 

[JohnD]

what percentage water did you add to your mist coats?

did the plasterer use glue?

how long did it dry before going pink?

 

[Wayners]

Get cheap orbital sander over that (120 - 180g) then prime with acrylic primer undercoat with 20% water.
Plaster paint is to allow walls to dry out over the next few weeks / months and not great for mist coating imo and manufactures say the same. Although many disagree and use.
These plaster paints are a tad rough and chalky to touch and some better quality emulsions need mist coating over plaster paint so you've not moved forward. Might as well mist coat with your chosen final paint.

Think the polished spots have caused you trouble there.
Lights sand and prime again with either your final top coat paint following guide or acrylic primer.
All covered here.

 

[Mat1980]

what percentage water did you add to your mist coats?

did the plasterer use glue?

how long did it dry before going pink?

I actually used plaster paint instead of a mist coat. I believe he did use glue, whole house was replastered. Can't say how long it took but it was weeks ago!

 

[Mat1980]

Get cheap orbital sander over that (120 - 180g) then prime with acrylic primer undercoat with 20% water.
Plaster paint is to allow walls to dry out over the next few weeks / months and not great for mist coating imo and manufactures say the same. Although many disagree and use.
Lights sand and prime again with either your final top coat paint following guide or acrylic primer.
All covered here.

Thanks that makes sense, will the acrylic primer sort the mapping?

We've only done two rooms so far. Assuming we'll have the same issue all over on the bare plaster how do we go about things for the rest of the house? Acrylic all over?

 

[Wayners]

Yeah.. Go pick up a 2.5lt and try it.
Here is a ceiling I mist coated with acrylic primer undercoat. 12 inch roller but bigger the better. Then top coated with paint no thinning sometimes. Depends on paint

 

[JohnD]

if there is any glue remaining on the surface of the plaster, scrub it with water and rub off with and old towel.

If it is thick, you can spray it with water and scrape the sludge off with a broad metal scaper. This is more often the case with old wallpaper paste. Plasterers like to use PVA.

 

[Wayners]

It's only neat pva that's causes problem with emulsion. If you look on YouTube there are tests painting over pva. I've skimmed and painted 100s and never once had pva caused me trouble. I often sand off though even after I skimmed but I've got all the kit Inc vacuum. I've had the odd over polished bit that looks similar to the op picture but I finish my skims with plastic blade which helps give a matt finish. I'm not brave enough to use pva as a plaster sealer but on yourtube some do. That's a risky game imo. I stick to the data sheets spec and products

 

[Mat1980]

Yeah.. Go pick up a 2.5lt and try it.
Here is a ceiling I mist coated with acrylic primer undercoat. 12 inch roller but bigger the better. Then top coated with paint no thinning sometimes. Depends on paint

Looks great!

I think I'm getting the idea now.

Do I need to sand the bare plaster before applying the Acrylic primer/undercoat or just wipe down?

Just the single 80/20 coat before top coats?

Any particular brands best?

 

[Wayners]

Leyland acrylic primer.
If all good don't sand.
Yeah one coat. Can give it 2 but second coat dont do you much. You will find that if you try