Newly plastered walls – some spots don't take paint

[thesheep]

I've been wondering about this for a while and thought I'd ask people here.

We've had a couple of rooms plastered – very good plasterer. But I always seem to find a few spots and areas where the mist coat doesn't seem to 'stick'.

After the plaster has dried I prepare for painting by giving the walls a light sand to key in (the fresh plaster is quite shiny) and then wipe down thoroughly to remove all dust. Then I paint with diluted matt emulsion for mist coat.

But in some distinct areas the paint refuses to 'take'. Feels almost like there is oil on there, or something like that. See photos below. Some of them at least appear to be 'drip' shaped. They do eventually go away if you paint over them about 6 times with thicker paint.

Anyone know what this is, and the best way of dealing with it?

 

[joe-90]

It's PVA from the plasterer.

 

[thesheep]

Ah OK. So when does he use that and why has it got on the surface of the plaster? Is this something that he's doing wrong (if so I will let him know).

Also, any tips what to do in this situation (other than just trying to repeatedly paint over it)?

Thanks.

 

[vibrobullit407]

Touch up the effected areas with a bit of oil based undercoat and leave to dry. You can then emulsion over the top!

 

[joe-90]

It's pretty much normal to get a few splashes here and there, not worth mentioning.

BTW get a roller on the wall those brush marks are horrendous.

 

[thesheep]

BTW get a roller on the wall those brush marks are horrendous.

I was told somewhere (can't remember now) that for the mist coat it's a good idea to use a brush, as it somehow helps the paint penetrate. Obviously I use a roller for the top coats. Is it just as good to use a roller for the mist coat too? If so, maybe I will switch to use that – would save a bit of time.

 

[thesheep]

Touch up the effected areas with a bit of oil based undercoat and leave to dry. You can then emulsion over the top!

Brilliant tip – thanks!

 

[vibrobullit407]

I use a roller for misting, always have!

 

[joe-90]

Roller is best - three coats in quick succession and it'll look painted before you think about the top coat.

 

[thesheep]

I use a roller for misting, always have!

OK cool, maybe I'll give it a try.

Doing a bit of Googling I see that some people do use a brush for the mist coat, the reason given seems to be that it is less messy than a roller.

 

[owainglyndwr1416]

I've been wondering about this for a while and thought I'd ask people here.

We've had a couple of rooms plastered – very good plasterer. But I always seem to find a few spots and areas where the mist coat doesn't seem to 'stick'.

After the plaster has dried I prepare for painting by giving the walls a light sand to key in (the fresh plaster is quite shiny) and then wipe down thoroughly to remove all dust. Then I paint with diluted matt emulsion for mist coat.

But in some distinct areas the paint refuses to 'take'. Feels almost like there is oil on there, or something like that. See photos below. Some of them at least appear to be 'drip' shaped. They do eventually go away if you paint over them about 6 times with thicker paint.

Anyone know what this is, and the best way of dealing with it?

Firstly there is no need to sand down new plaster before applying the Mist Coat as sanding even with 120 grade Sand paper leaves scratches on the surface.. The idea behind Mist Coating is to prime coat the Wall with a thin breathable good quality High Opacity Emulsion which does 3 things..Firstly it primes, Secondly it highlights imperfections like stray lumps of plaster which are easily scraped off and thirdly it allows you to fill any defects and sand easily prior to finishing with a good quality Vinyl based Emulsion .. The areas that you are concerned about are in fact of no concern at all . They might look unsightly but it does not effect the way subsequent coats of paint behave..