Crumbling cornice

Hudson Valley

New Member
Hi. We had a new house plastered— walls, ceilings, and cornice— 17 years ago. It was done by an older plasterer who came out of retirement for the job. He did beautiful work and it has worn well except in one spot.

A year ago a section of cornice over the stairs began to blister and crumble, not big chunks but small bits of dust and chips. We cleaned it up a bit and left it alone even though it looks terrible. It mostly stopped shedding plaster onto the stairs until yesterday when it suddenly started again. It’s very humid here now.

Any thoughts about what could cause this? There is no source of water leaking in that area and no staining.
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MakeItSmooth

Well-Known Member
Is there a cold water pipe in that ceiling?

Just wondering about condensation, given that it's happening during warm weather.
 

The Hobo

Well-Known Member
presume its a fibrous plaster cornice they don't like humid conditions /are you sure there is no damp on the wall or ceiling as I see a mark on the ceiling possible cause could be from the kitchen if the door is open to the stair when cooking and the moist air is getting trapped in the corner /seen similar in shower rooms /try opening a window when cooking you could try cleaning it down then filler if needed then gloss paint it before re emulsion it
 

Hudson Valley

New Member
It does look like water damage, but there are no pipes above it and no water damage or staining on the wall or ceiling. We’ve looked in the attic and it’s dry above.
The cornice was not a prefabricated moulding. It was run in place with plaster and a profiled mould.
I’m wondering if there could have been a problem with the mix in that section? The rest of the cornice over the stairwell and throughout the house is fine. It’s about a four foot section on one wall and a little bit turns the corner onto the adjacent wall.
thanks for the help!
 

The Hobo

Well-Known Member
It does look like water damage, but there are no pipes above it and no water damage or staining on the wall or ceiling. We’ve looked in the attic and it’s dry above.
The cornice was not a prefabricated moulding. It was run in place with plaster and a profiled mould.
I’m wondering if there could have been a problem with the mix in that section? The rest of the cornice over the stairwell and throughout the house is fine. It’s about a four foot section on one wall and a little bit turns the corner onto the adjacent wall.
thanks for the help!
sorry but that being the case you have a source of dampness some where post a photo of outside wall roof and gutter area
 

John j

Mono Don
sorry but that being the case you have a source of dampness some where post a photo of outside wall roof and gutter area
What I thought. Also what if the insulation been pushed up tight. If this is upstairs . Could that cause condensation
 

The Hobo

Well-Known Member
What I thought. Also what if the insulation been pushed up tight. If this is upstairs . Could that cause condensation
no its pulling damp from somewhere the cornice has a lot of lime content in it which acts like a sponge pulling the damp to it that's why its not showing much on wall and ceiling
 

Hudson Valley

New Member
It’s in the middle of the house, not against an exterior wall. We have the same cornice in the bathrooms with showers with no problem. There is air conditioning duct in the attic above, nothing else. Could that produce enough condensation to do this? Thanks for all the input.
 

Hudson Valley

New Member
Another question. If we do find a source of moisture and mitigate that, should we remove all the existing plaster and start fresh or can we scrape off what’s flaking and add more on top? Is there some sort of barrier coating we should add between? Thanks again.
 

The Hobo

Well-Known Member
Another question. If we do find a source of moisture and mitigate that, should we remove all the existing plaster and start fresh or can we scrape off what’s flaking and add more on top? Is there some sort of barrier coating we should add between? Thanks again.
have a look at Zinsser grade 1 sealer /scrape sand and fill no need to remove /cant comment on vent /but its a damp issue I have spent 55 years on older houses /if you find out cause please post the result be interesting good luck
 
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