Skimming on top of emulsion

[BotchItYourself]

I wish to skim over a wall which currently has several coats of emulsion on it. Plasterer suggested that I coat the surface with PVA (he suggested undiluted !). He will then apply another coat of PVA immediately prior to applying the skim. Is this sufficient preparation to prevent the skim blowing soon afterwards ? I suggested scoring the surface or mixing sand with the PVA but he said neither was necessary. I have had other walls skimmed over existing plaster and have often had lots of hairline cracks appear once the new surface has been painted so I'm worried that his suggestion may not work. Any views ?

 

[marshman]

every plasterer is slightly different I like to prime walls with it diluted 3&1 to 4&1 the day before some times 2&1 if the under plaster
is bonding or browning and any dust or grit the better, I guess he just wants to make sure you seal it, neat pva will be hard to spread
as a first coat.
no offence meant but we've all had job were the customer has said they'll do it but only does half of one.

 

[Richard C]

Without seeing it, sounds about OK to me. If it’s just ordinary emulsion; 5:1 PVA once let it dry, PVA again, let it go tacky & skim away. It’s vinyl emulsion you have to be a bit careful with; I always score it thoroughly the day before with a very stiff wire brush, then 3:1 PVA & leave to dry overnight followed by a 5:1 PVA next day, let it go tacky & skim.

 

[BotchItYourself]

Thanks both of you for your replies. I'm reassured.

Just to be clear. In the light of my plasterer suggesting undiluted PVA, when you state 3:1, 4:1 or 5:1, do you mean 5 PVA to 1 water or 5 water to 1 PVA ?

 

[Richard C]

5 water to 1 PVA

 

[Softus]

If it were mine I'd want to do some serious scratching and raking of the painted surface before applying dilute PVA. But that's just me.

If you trust the plasterer then do exactly what he says - if it falls off or cracks then it comes down to him.

 

[BotchItYourself]

Thanks Richard.

Softus, I'm minded to do that anyway. After all, it can't do any harm, can it ? Precisely what do you mean by "serious" ? Should I just scratch the paint with a brush or cut into the plaster with a knife ?

 

[Richard C]

Should I just scratch the paint with a brush or cut into the plaster with a knife ?

I would just add that my stiff wire brush is VERY stiff; I've also used the corner of an old scraper before now & gone over the wall criss-cross fashion.

 

[Softus]

Softus, I'm minded to do that anyway. After all, it can't do any harm, can it ?

I quite agree.

Precisely what do you mean by "serious" ?

Apologies for the nebulous nature of that adjective - it was unforgivably vague.

Should I just scratch the paint with a brush or cut into the plaster with a knife ?

Knife, or corner of scraper, á la Richard C.

A knife has the advantage of instantly revealing any patches of paint that weren't very well attached - they flake off when you score them.

 

[clout stench]

You say the paint had hair line cracks all over it when you painted fresh plaster before. Did you seal / prime the new plaster before painting?

 

[GaryinAshby]

A friend taught me a trick to removing old paint from plaster. Score it with a knife in a criss-cross pattern, lots of times, ideally each score line 1/4" from the next. Then use brown parcel tape & tape over the entire surface, tow layers, each at 90 degrees to the other. One edge of the taped area should have the tape folded back onto itself so that there is an entire edge where 1/2" or so isn't stuck down. Then leave it for a few days before peeling off the entire area, peel it off quickly. Its amazing how much of the old paint comes off.

 

[BotchItYourself]

You say the paint had hair line cracks all over it when you painted fresh plaster before. Did you seal / prime the new plaster before painting?

Yes, either with plaster sealer or with diluted emulsion depending on what I had available at the time.