Need advice on chipping plaster


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Old 04-11-10, 01:23 PM
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Need advice on chipping plaster

Hello everyone, I'm new to this site and wanted some advice on a small problem I'm having with interior plaster. I uploaded some photos on this site to help explain:

ImageShack Album - 4 images

My wife and I own a 50s era home. Our interior walls appear to be a light coat of plaster over the board. We have also painted over the plaster.

We recently noticed that the paint was cracking on one wall near the top corner. Not just the typical plaster crack; it looked like the paint was "peeling" from the wall. I wanted to get under it and take a look, and once I started chipping away I realized it wasn't just paint, it was the layer of plaster.

I chipped all the loose stuff I could get to and sanded around the edges. The strange thing is how clean it came off from the wall. It's almost like the plaster wasn't adhered at all. There was no discoloration or appearance of water damage. I crawled in the attic to take a look at that corner and didn't notice any water damage.

We have put on one coat of Rapid Coat Joint Compound, and plan on putting on 2 more then painting over. I think this should hide the damage well.

My concern is that I don't have any idea why this could happen, and if it happened once it could happen again. I can't really keep chipping a larger section of plaster every time and patching it up. Also, if it happened in one place could it happen somewhere else? Is it possible the person who installed it originally did something incorrectly?

Any advice is appreciated. Thanks.
 
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Old 04-11-10, 04:39 PM
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What's on the other side of that wall? In any event, if it cracks again, cut the section to the studs & replace it with dry wall.
 
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Old 04-11-10, 07:32 PM
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not sure whats there

looking at your photos i have to ask whats there below the part thats peeled off. to me that looks like plaster. what can happen is a reaction between layers caused by the lime. case in point bout 15 years ago did a side job with a journyman plasterer. when we did our scratch coat (grey base plaster that looks like cement) he mixed his own ratio of lime. he said it was to make sure we did the top coat. long and short of it another crew of contractors were hired for top coat and sure enough their plaster peeled off after curing. you can use setting type mud but if it ever gets moisture in there again the lime will turn it to powder. the best bet is to seal the hole before you fill it either paint over with a good primer and let dry before patching or buy a product such as liquid lath. this will seal between layers and protect the repair.
 
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Old 04-12-10, 03:40 AM
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Originally Posted by Pulpo
What's on the other side of that wall?
This wall is an exterior wall.
 
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Old 04-12-10, 06:12 AM
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If it's an exterior wall, go outside & inspect the corresponding section.
 
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Old 04-12-10, 05:49 PM
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I checked the exterior wall. There doesn't appear to be any water damage. I also checked the Attic once more just in case I missed anything. I couldn't find any sign of water damage there either. I pulled up some of the insulation and found nothing strange.
At this point, I really just wonder if someone else has had this problem and what they could find out. I don't mind patching up this one place and a few more if necessary. But I just would like to know why it could happen and what should I do long-term.
Thanks for the advice.
 
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Old 04-12-10, 05:55 PM
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Originally Posted by uncledaddy426
looking at your photos i have to ask whats there below the part thats peeled off. to me that looks like plaster.
I *think* it's just unfinished drywall with a thin coat of plaster over it an a few layers of paint.

I wonder if someone had put too little a coat of mud on before taping when the wall was plastered originally. I read that could cause blistering later. It seems to be my problem (blistering). Then maybe it separated further and further down the wall until it cracked.
 
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Old 04-12-10, 10:31 PM
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I think you have gypsum plaster with a whitecoat finish. Whitecoat is a mixture of lime putty and gauging plaster. There are a couple reasons why the finish could come off the basecoat. Did the house go through a winter unheated? Can you describe what is under the peeled material? Does it look like it has sand in it? How smooth is it?
If you rub your hand over it does anything rub off?
How thick is the layer that is peeling?
What I would do is scrape around all the edges and see it anything else is loose. Take it off it it is. Don't work too hard at it. You can probably scrape off the whole wall. What you want is to get off anymore that is loose.

An amateur friendly way of fixing it is to use quick setting joint compound to fill it to level with the existing. Spread on a coat and screed it off flush with the existing. Then just as it sets smooth it off with the trowel.
After it has set give it a coat of regular joint compound, let it all dry then sand, touch up and prime and paint.
 
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Old 04-13-10, 05:24 AM
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tightcoat,
I was told never to use setting compound & drying compound in the same place, since one sands more quickly than the other. Why do you recommend that
 
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Old 04-13-10, 05:21 PM
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The setting compound builds up a little. It looks like this is a plaster finish coat 1/16" to 1/8" thick. To put that much joint compound on in one coat would let it shrink. Setting mud won't shrink and if multiple coats are needed to fill it flush they can be done in rapid succession. That is as soon as one coat sets the next coat can be applied.

Yes, setting mud is harder than ordinary. The reason I suggest finishing with ordinary is so that if sanding is necessary it will be easier to sand.
 
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Old 04-13-10, 07:25 PM
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I prefer setting mud all the way. It's just my preference.
 
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Old 04-13-10, 09:17 PM
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IF I am right that this is plaster, and IF I were doing the repair, assuming I am right, I would use whitecoat and be done with it. But the original poster has not convinced me which it is so I assume he is an amateur and I gave him what I consider a more amateur friendly procedure.

If one uses quickset and if he wet trowels it just as it sets (but there isn't much time to do this) one can get that hot mud to lay down almost as slick as whitecoat, which is to say almost as smooth as glass. But if it doesn't work like that then a coat of ordinary mud can fix the flaws and be more sandable.
 
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Old 04-13-10, 09:40 PM
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That makes sense.
----------------
 
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Old 04-15-10, 04:53 AM
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i still would seal the basecoat before the repair. we get alot of waterdamage due to ice dams where i live, and sealing the basecoat seems to be the difference in having to do an area again.
 
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Old 04-15-10, 10:21 AM
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IF it is plaster and IF the repair is done with authentic plaster materials and IF it is "sealed" it should be done with a plaster bonding agent like Plaster-Weld by Larsen's products. There are other brands.

If drywall materials are used it should be sealed with a suitable sealer as uncledaddy suggests.
 
 

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