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I've just finished a renovation of my house. In the new half of the house, we have had problems with the paint on our cornices cracking. The cornices were brand new when installed, this was done months before painting and they seemed in good condition. Our first painter painted them at the same time as the ceiling - the cornice paint is now cracking but the ceiling paint is fine. The numerous cracks are fine and short (perhaps 3~5mm long). The only room upstairs that the paint is not cracking on is in the bathroom which was painted with mould resistant paint.

We had the same corninces installed downstairs and had a different painter paint them - they have had no problems.

Do you have any idea what may have gone wrong? Our painter swears he did everything perfectly.

Do you have any idea how to fix this? They are decrative corninces so sanding back is not really an option.

Needless to say, we've been having fights with our painter over this.

The original cornices are 90 years old and they are fine as well.

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Was it the same paint as the ceiling? –  Renshia Dec 20 '10 at 5:28
    
also what material are they made out of? –  Renshia Dec 20 '10 at 5:31
    
sorry I see you mention in the main title plaster. –  Renshia Dec 20 '10 at 5:36
    
Yep, the cornices are plaster. –  dave Dec 20 '10 at 21:21
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2 Answers 2

The cracking would imply a drying problem. I would think that the cornice was primed improperly. If the primer was of cheap quality or the painter used a paint with a built in primer for drywall. The primer may have not effectively sealed the plaster. Then the drying of the paint would be effected, basically the plaster sucking out the moisture to quickly. this could cause the paint shrink and crack as it dried.

Answer to comment.

You have to fill the cracks. either by sanding them out or filling them. If sanding isn't an option try coating an area with a light coat of mud and after it drys lightly wipe it smooth with a damp cloth. Then repaint starting with a good sealer, kiltz would probably do.

A type of self leveling paint might work without all the mud filling, but It depends on the size of the cracks. I would sample a couple areas to see what works best.

There are paints that claim to have this ability. I would still start with a good primer/sealer before anything.

Cashmere

This is not an endorsement of the paint only an example of what to look for. I have never used it.

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Agree. sure sounds like the paint dried too fast. Is there a chance that an oil based paint was applied over a latex or PVA primer? –  shirlock homes Dec 20 '10 at 9:44
    
I don't think so. The painter swears blank and blue that he did all the right things. Given how quickly they cracked (major problems in weeks), then drying out too fast seems likely. But how do I fix this? –  dave Dec 20 '10 at 21:13
    
Doing things right is relative. If you do all the right things but use wrong materials or cheap materials, you can still end up with a crappy result. Not that I think this guy did anything wrong, sometimes things react in unexpected ways. –  Renshia Dec 20 '10 at 22:13
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up vote 0 down vote accepted

Thanks guys, we had a professional painter come through. He said that it looks like the cornices were not sealed correctly - either too thin or with a cheap undercoat. He reckons that he would normally apply two coats of undercoat and one of paint just to make sure it takes.

His suggested solution is to wait a few more months. The cracks will continue for a while then stop. When they have stopped, the cracked paint needs to be flaked off and hit with two coats of undercoat and repainted.

This is just his opinion, but seems to square with what we've been told by others.

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