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repair of cracks in horsehair plaster walls

phyllis1954's picture

I have a big old house built in 1850 interior of horsehair plaster. What is the best and easist way to repair these and what are the names of products I buy?  I also need to clean these walls to paint, I have heard of TSP and dirtex.  Would this work on these old plaster walls?  I have heard of Easysand 90 and durabond also for these cracks.  Do I use just the plain paper to cover the cracks with after sealed?

Sorry for so many questions.  I would appreciate any and all ideas.

Thanks, Phyllis

Fiberglass Mesh can help (post #206970, reply #1 of 7)

An easy way is to cover the entire wall in fiberglass mesh.  Can get 3 foot rolls of it at Home Depot nowadays.  Then skim coat the whole thing.  Some people go as far as applying the mesh, the coating the entire thing with pink plaster adhesive.  It has tremendous bonding capabilities and is meant to bond well with plaster and drywall compound. The mesh reinforces the coat of compound applied to it and there is no need to go digging out each crack and filling them.  Been doing this since 1998 on really old houses in Maine with no problems yet.

Loose horse hair (post #206970, reply #2 of 7)

I drill 3/8 hole down the crack in the horse hair, spacing the holes to land at the lathe and then squeeze ample amount of construction adhesive into the holes. Then screw in screws down the length of the crack. Let the adhesive set up for a day and trim flush any adhesive that oozes out. I suspect you could use spray cans of form insulation also. Good luck.

Iwo (post #206970, reply #3 of 7)

I would suspect the spray foam to bond, but would think the expansion of it could push off the plaster from the lath keyway if not used sparingly.

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It really depends on how (post #206970, reply #6 of 7)

It really depends on how badly cracked the plaster is.  If it's only a few cracks, I've had really good luck with opening up the crack with a belt sander with a 36g belt.  I'll then build the void back up with setting compound and finish off with mesh and pre-mix.  Applying the tape directly over the crack does not work because the joint isn't thick enough.

If the cracks are really bad, then you might be forced to use drywall over the plaster to rebuild the whole surface.  Mouldings at the wall-ceiling joint can be added to hide the joint.  If height is critical, 1/4" or 3/8" drywall can be used, but strangley, 1/2" is cheaper.

Remember, if the cracks are really bad, that the keys are proably already busted off.  This means the plaster could be ready to fall.


The spray foam won't push the plaster off (the keys wil hold it), but it will warp the lath causing the keys to break thus releasing the plaster.  I've seen cavities foam insulated behind the plaster, but it takes a lot of holes to evenly distribute the foam and even then there will be a cavity that doesn't get insulated.

I saw a product on This Old (post #206970, reply #4 of 7)

I saw a product on This Old House Hour that I can vaguely remember.  It involved screws and glue, and some type of fixture.  I would look at their website and see if you can find it.

OK, I went ahead an found it for you,

It seems a little high priced to me, but it would help you fix your walls.

Those washers are just (post #206970, reply #5 of 7)

Those washers are just "plaster" washers -- readily available in metal (which is probably superior to their plastic ones).  Dunno what the adhesive might be.

Of all the preposterous assumptions of humanity over humanity, nothing exceeds most of the criticisms made on the habits of the poor by the well-housed, well-warmed, and well-fed.  --Herman Melville

Well, the idea is that the (post #206970, reply #7 of 7)

Well, the idea is that the washers are removed and the screw hole is spackled over after gluing.  The metal ones if left in place are spackled over, but if they aren't countersunk it would take a bit of creative work to hide them.  I know notthing of the other components of the "system".