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Plaster Weld and skim coating old wall

BobChapman's picture

I'm working on an old house with horsehair plaster walls and ceiling.  I'm attaching some loose plaster with plaster washers, which  protrude from the wall about 1/8" after they are installed.  The plan is then to skim-coat plaster over the wall, deep enough to cover the plaster washers.

I'd like to use Plaster Weld, a sort of bonding agent that you roll onto the wall to make sure that the new plaster adheres properly to the old wall.  BUT, the Plaster Weld container, and the website instructions, say to use a 1/8" finish plaster coat on top of the Pllaster Weld coating.  They don't say if the 1/8" is the minimum or the maximum finish coat to put on.

I have put this question to the manufacturer, but it doesn't appear that I'm going to get an answer as soon as I need in order to keep going on this job.

Does anyone here have experience with this product?  can I put on a 3/16" thick finish plaster coat, which would be thick enough to cover theplaster washers, and be OK?

Thanks for your help

Bob Chapman

(post #107582, reply #1 of 7)

Yes and Yes, I just left a big job where the best plasterer in this area was doing similar, much thicker than that and you may have sag issues.

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(post #107582, reply #2 of 7)

When I've used plaster washers, I usually use a Forstner bit, and drill into the plaster a 1/16" to 1/8" or so.

That way the washers are recessed, and you don't need a heavy coat of plaster to cover them.

I tried using a spade bit, but I found the long center point makes too big a hole in the lath for the screw to grab well.

Its messy, but I find it saves time in the long run. But be careful about leaving enough plaster so that the washers don't pull thru.

(post #107582, reply #3 of 7)

I second what Sphere said. I think sag is one problem you might encounter if it is to thick. But another issue is that in plastering a whole house they wouldn't want to get  the top coat to thick due to cost. We're talking a lot of materials. So an 1/8" is ideal for putting a top coat over the layer under it.

With that bonding agent under your top coat it might not dry out as quickly as it normally would. It's more of a wicking out of the moisture by the plaster coat under it than drying. 

I'm no expert on plastering but have done a little and seen it done to a whole house.

______________________________________________________________ ______________________________________________________________ There are three kinds of men: The one that learns by reading, the few who learn by observation and the rest of them have to pee on the electric fence for themselves. Will Rogers

(post #107582, reply #4 of 7)

I concur about counter-sinking the plaster washers.

But you can use Acryl60 as the bonding agent. Mix it with water and then mix the mixture into the plaster. This makes it one step instead of two.

(post #107582, reply #5 of 7)

Not what you're asking about, but just my 2c. worth. I can't count how many old plaster walls I've worked on, and I've never had a bonding issue with Easy Sand 45 or 90. Takes a couple or three coats, but sand smooth, prime and paint, simple.

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(post #107582, reply #6 of 7)

I think you're fine - here's my way -



(post #107582, reply #7 of 7)

Thanks everyone for your views.