Crazed emulsion on chimney breast.

[amfisted]

Hi All

Had a multi fuel stove fitted about eight weeks ago. The fireplace opening was enlarged to take the stove and the installers finished off the plasterwork to a good standard. I left the plaster for a few days to allow drying out then applied matt emulsion with a roller.

Since the paint was first applied I've had problems with the surface crazing, but on only one side of the breast. The other side is perfect. I've tried rubbing down the crazing, sealing with bonding agent and repainting. I've tried taking off the plaster in the crazed area then replastering with one coat plaster and repainting. However, the crazing always comes back.

I'm tempted to leave things till the weather improves, take the surface down to the brick and start again, but it seems like a lot of trouble to go to just for a decent paint surface.

Is there any other treatment or procedure that I could try to get a decent finish? I initially thought that the crazing might be caused by heat from the stove, but if that was the case then both sides of the breast would be affected.

Cheers in advance.

 

[JohnD]

did anybody put glue on the wall?

Did you apply a mist coat?

Was the new plaster dry pink, or brown patches?

 

[amfisted]

No glue has been applied to the wall to my knowledge, and the new plaster was pink.

No mist coat was used; the paint was applied straight out of the tub. Would it be worth rubbing down and starting from scratch with a mist coat?

 

[Pigeon85]

No glue has been applied to the wall to my knowledge, and the new plaster was pink.

No mist coat was used; the paint was applied straight out of the tub. Would it be worth rubbing down and starting from scratch with a mist coat?

Yes always apply a mist coat to new plaster using matt paint, depending on what paint you use it could be anywhere between 50/50 and 70/30 paint to water.

Best to apply to a small area to make sure it absorbes into the plaster.

 

[amfisted]

Thanks for that.

I was aware of the well-established practice of diluting water-based paint when applying to a surface which is new or of questionable stability, but never heard it described as a "mist coat" until fairly recently. It just didn't occur to me to use it in this case.

 

[chappers]

I doubt that's what's causing the crazing though. Especially since you have re-plastered.
I know you have ruled heat out, but it seems the most likely explanation to me, either that or there is something fundamentally wrong in the backing, is the crazing only appearing in the paint finish or is it visible in the plaster.

 

[JohnD]

sealing with bonding agent

what did you use?

 

[amfisted]

I doubt that's what's causing the crazing though. Especially since you have re-plastered.
I know you have ruled heat out, but it seems the most likely explanation to me, either that or there is something fundamentally wrong in the backing, is the crazing only appearing in the paint finish or is it visible in the plaster.

The crazing is in the paint only.

I think my best bet is to leave it now until the weather is warmer and the stove no longer in use, then rub down and paint the entire surface again with mist coat then full coat. At least then I can eliminate the heat as a causer of the crazing.

 

[amfisted]

what did you use?

Something similar to Unibond. I think it was an Everbuild product.

 

[JohnD]

PVA glue.

Case solved.

 

[amfisted]

The initial problem was blistering of the paint, which I guess was caused by not using a mist coat for the first application. I dealt with this by first scraping off the blistered paint, then filling the holes with a skim of filler, sanding down the filler once dried, applying PVA, allowing that to dry then painting over. That's when the crazing appeared, so you could be right.

 

[sb88]

Replying to this old thread to counter all the suggestions of PVA, sealer etc.

Heat from the new stove is possibly forcing out long-standing moisture from the brickwork and recent residual moisture from plasterwork, which is getting trapped under a modern plastic paint which has no choice but to life. Maybe happening on one side as flue may veer to one side inside stack to accommodate the flue from fireplace in the room above?

Covering it with ever more plastic and sealant type paints will only prolong the issue.
Scrape off paint, dry out thoroughly and repaint in a breathable (e.g. clay) paint. Explore any further causes of damp ingress e.g. chimney stack.

Same thing happened in my house where prior owners had used an inappropriate paint for an older property. After using the log burner in the winter, the crazing appeared,as it did above the radiator. When the radiator was off, you could peel paint off and tell the plaster was damp. Painting over it with same paint would have solved nothing. Same happened in early summer as hot weather caused the South facing wall to warm and dry out.

I'd suggest heat alone unlikely to be sole cause. A thermometer on my chimney breast only gets to 25-26 degrees. The air venting out of the back of my games console towards a wall 4 inches away is hotter than that, and the paint hasn't peeled.

 

[amfisted]

Replying to this old thread to counter all the suggestions of PVA, sealer etc.

Heat from the new stove is possibly forcing out long-standing moisture from the brickwork and recent residual moisture from plasterwork, which is getting trapped under a modern plastic paint which has no choice but to life. Maybe happening on one side as flue may veer to one side inside stack to accommodate the flue from fireplace in the room above?

Covering it with ever more plastic and sealant type paints will only prolong the issue.
Scrape off paint, dry out thoroughly and repaint in a breathable (e.g. clay) paint. Explore any further causes of damp ingress e.g. chimney stack.

Same thing happened in my house where prior owners had used an inappropriate paint for an older property. After using the log burner in the winter, the crazing appeared,as it did above the radiator. When the radiator was off, you could peel paint off and tell the plaster was damp. Painting over it with same paint would have solved nothing. Same happened in early summer as hot weather caused the South facing wall to warm and dry out.

I'd suggest heat alone unlikely to be sole cause. A thermometer on my chimney breast only gets to 25-26 degrees. The air venting out of the back of my games console towards a wall 4 inches away is hotter than that, and the paint hasn't peeled.

Thanks for taking the trouble to revisit my historical thread and for your input.

As an update, the surface has been relatively stable since I took the surface back down to plaster in those areas where the problem had occurred, and then reapplied paint with an initial mist coat. I'd never actually heard of the term "mist coat" nor used one until this particular issue arose.

I tend to agree that heat isn't the problem. There's been no crazing in the area most directly exposed to heat, and the worst of the problem was on the right hand side of the breast, level with the stove rather than above it.

I noticed a minor, localised recurrence of the problem late last year so I removed the paint, dug out the plaster, applied filler, rubbed down then mist coated and repainted the entire chimney breast and all good so far. We're in the process of selling the house so hopefully the surface will remain stable for the new owner.