Help! Paint bubbling while painting new plaster

[philipb82]

Hello, i started painting new plaster with Dulux white matt emulsion watered down by 20%. As i was applying the paint with a roller it bubbled in places and came off with the roller. I've painted other new plastered walls in the same room with no problems. What could be causing this? Thanks. Phil

 

[philipb82]

Most of the mist coat has dried but the offending paint was quite soft. I've scraped that off with ease as far as it goes. The area of plaster was quite dusty like plaster dust but i ignored this and painted anyway.Could this be a possible cause? Help please! Phil

 

[jackassofalltrades]

I would say there is to much water in the paint, make sure the paint and water are mixed together really well, stir it for a good 4-5 minutes.

Do you give the walls a light sand and wipe down?

 

[misterhelpful]

Yes, the dust is the most likely cause. Always clean excess dust off any surface you are painting otherwise you are virtually guaranteeing adhesion problems.

The typical result of painting over dusty plaster is initial coverage but peeling off as you re-roll over the area. Is this what happened to you?

Allow the current paint to dry and lightly sand the area to feather in the edges and get it smooth. Wipe off the excess dust with a damp cloth and again allow to dry. Mist coat the patch and when totally dry it should be fine to accept the finishing coat/s.

 

[philipb82]

Thanks for your replies. I didn't sand or wipe the wall down i just applied 2 mist coats. I know now i should have wiped that dusty area! That sounds like the cause. Do you think i've added too much water? I've read that because dulux is quite thick you can a bit more water. Thanks. Phil

 

[misterhelpful]

Do you think i've added too much water? I've read that because dulux is quite thick you can a bit more water.

I, and most decs, use contract matt for mist coating watered down 10-20%.
As you say, Dulux is quite thick, so watering it down by the 20% you said shouldn't cause a problem. In fact, you could probably go up to 25% water, but as I say, I always use contract matt for misting.

 

[philipb82]

I have wiped down the dusty area twice and it has re-appeared. It looks like its in the plaster if that makes sense. Phil

 

[misterhelpful]

Is the plaster fully dry or in an area that has been damp previously? Moisture in the wall can cause a similar situation.

Any chance of posting a pic?

 

[philipb82]

It sounds like it could be a damp issue. I got the plasterer back round today he checked the outside wall and there was a powdery substance on the render. Anyway hes coming back in the morning to apply this clear damp seal called thomson/thompson. Then some watered down pva to seal the wall. All this under guarantee. Its a bit difficult to post a pic cos i only have internet on my phone! Phil

 

[misterhelpful]

Then some watered down pva to seal the wall.

Hope that doesn't mean on the plaster because you are likely to make the situation worse. PVA is not suitable for use with paint but some people will argue otherwise. Check the tin/bottle before applying it but the choice is yours.

 

[philipb82]

He didn't put any pva on. He just brushed on some Thompson one coat damp seal ultra so hopefully that should sort it. I asked him if i still need a watered down first coat of paint but he said neat will be fine. Phil