1950s Rock Lath-HELP!


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Old 05-03-21, 07:06 PM
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1950s Rock Lath-HELP!

I have a 1950s house that uses gypsum rock lath with plaster coat on top. In one room in particular, the top plaster coat was loose when I painted it in 2008 after buying the house. At the time I used joint compound to skim coat the surface to be smooth. Two years ago when I repainted, I noticed the compound had cracks. The area was once again loose. I again scraped it all off, then I primed and used a setting compound. Now that job is cracking and coming delaminated in places(not all -yet). I have removed all the baseboards to paint the room again. In some areas the old original top coat is loose (picture). I can flake it off with a putty knife and it does not seem to end

Original , delaminated top coat.
. Does anyone have any suggestions? I do not want to gut the room and drywall. I tested an area with plaster of paris and that seems to be drying very hard. Should I keep removing the loose stuff or stop and seal it somehow? Any tips would be much appreciated!
 
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Old 05-03-21, 07:31 PM
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What's on the opposite side of this wall? And what is below? Reason I ask is that if this is an exterior wall, or maybe a bathroom, or there is a crawl space below, there could be a moisture issue leading to these failures.

Yes, you would obviously need to remove anything that is loose... you don't mud over anything that is loose... and you m would need to resolve any moisture issues (if that is what's causing it). Could be a lack of insulation on an exterior wall... or missing bottom plate... some air leak that is bringing high humidity along with it. (Looks like a hole big enough to fit your fingers into down by the carpet). If that is a hole, and it leads to a crawl space or damp area, that would need to be blocked off and air sealed.
 
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Old 05-03-21, 08:21 PM
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This particular wall is exterior. The house is on a slab. The holes you see are from removing the baseboard. There is no insulation in this wall, I wonder if that is what is causing the failure? The house is air conditioned so the inside does not get humid, and I do not see any water or moisture issues .When I say loose, I have to put the putty knife under it and it scrapes off. It does not feel hollow nor is it bulging anywhere.
Also, the other wall with the issues has a bedroom on the other side.
 
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Old 05-03-21, 08:29 PM
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Yeah, if you can get a putty knife under it and scrape it off, that is loose. In other words, its no longer bonded to the rock lath. You likely need to do something to increase the adhesion. After you scrape, and before you skim coat, you probably need to roll on a coat of Gardz or maybe just a coat of primer would do. Then skim coat, and tape cracks with Fibafuse (this product will lay really flat).
 
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Old 05-03-21, 08:49 PM
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What product do you recommend to skim coat? I tried the latex primer and setting compound before. It has all come off in spots, including the primer! At this point I am about ready to demo and drywall, but that is a huge mess.
Other info- the exterior is brick if that helps diagnose potential problems with humidity.
 
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Old 05-03-21, 08:56 PM
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Its not a surprise its not sticking to the exterior wall. Air conditioning on a warm uninsulated wall would likely cause condensation under the finish coat. But why the opposite interior wall is doing it is a good question.

Maybe try and use Kilz original oil based as your primer this time. I don't think the type of mud matters too much, but if you can put on a real smooth coat, you might use Durabond 90 as your first coat, followed by ordinary joint compound. Durabond 90 can't be sanded so don't leave any big ridges. Continue to smooth it as it starts to set. The wider the knife the better.
 
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Old 05-03-21, 09:01 PM
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Thank you for the tips. I have two other bedrooms adjacent with an uninsulated wall. I had a few trouble spots but nothing like this. I used plaster of paris in 08 in one. I remember it was hard to sand so that is why I switched to the compound. So far the plaster patch still feels solid. I have tried contacting a pro but no one has returned me calls.
 
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Old Yesterday, 02:27 AM
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A plaster guy would use real plaster but durabond is close and what I use when I have to repair plaster.
 
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Old Yesterday, 08:15 AM
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Marksr, I believe I used the USG easy sand 45 or 90 minute set last time. Is durabond different?
 
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Old Yesterday, 08:16 AM
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They are similar, Durbond dries a little harder. They all come in various set times.
 
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Old Yesterday, 12:21 PM
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What would you suggest I use to prime the base?
 
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Old Yesterday, 12:22 PM
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If the base is dusty I usually use Gardz or an oil base primer [whichever one I have handy]
 
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Old Yesterday, 12:35 PM
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Have you ever used the sealer products to apply to the edge of the existing coat? It is supposed to keep it from flaking, but others have said if it is loose enough to flake off with a knife it wont matter.
 
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Old Yesterday, 12:54 PM
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No, I've never used any plaster specific sealers - I'm a painter by trade.
There is a member named tightcoat that is a plaster pro, hopefully he'll have time to respond.
 
 

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