How do I patch a large hole in plaster and lath?

Question

I am having some plumbing repaired in my 1913 house that will result in a large access hole (2' x 16") on the first floor. The wall is currently plaster and lath and I'm trying to get a handle on the best way to repair the damage after the plaster and lath are removed. From what I've read so far, plaster of Paris hardens too fast, making it difficult to work with so I'm leaning towards DAP® Plaster Wall Patch (Dry Mix). I know I need to provide some backing material either metal or wooden lath but I'm not sure what else is needed. Do I need to use any fiberglass mesh to put over the lathe or can I just start with the plaster. Does anyone have any experience with the Plaster Wall Patch? Is there something better that would work? When applying plaster it sounds like I need at least two layers, once base and another finishing. Should I build up a first layer, let it dry and then another layer level with the existing surface or is there a technique that would be better. Do you think I can paint over the Plaster Wall Patch or is something else needed to prepare the surface for painting?

I can't wait to get started, I just need a little help in putting a plan together.

Answer 1

What I have done on my 1909 house (I am in the U.S.) in the same exact situation is clear a wider area of the lath and plaster and replace it with drywall. To do that, you will need to add some padding over the studs because the lath&plaster is thicker than 1/2" -- what I did was pad it with 3/8" plywood, then drywall over plywood to achieve approximately an even joint between the new drywall and the old plaster. Then you tape and sand the joints like you would with regular drywall, prime and paint it later.

Answer 2

I am a drywall and plaster contractor in Va. The guy above told you correctly. The problem with wood lath is: once you start to cut it or re-screw it back up where cracks are, the lath pulls away from the studs, causing the cracks to get worse. If you are determined to use plaster, you must use a bonding agent, plaster weld, for the new plaster to adhere to the old. Your best bet would be to use a product called easy sand. It is a drywall product that works the same as plaster (no bonding agent needed).

If you are going from room to room remodeling your house, you will be much better off gutting the entire room, hanging new wallboard and finishing it. Smooth plaster is very difficult especially for a home owner. With wood lath, it can never guarantee the cracks will not return. Gouging them out and mesh taping will not stop the cracks. Cracks are caused by movement, where the lath nails have pulled out from the studs.

Good luck.

Answer 3

I am a homeowner/hobbyist that loves fixing up old houses. Lath and plaster was a special challenge towards my endeavor to perfection. Many attempts at trial and error before this solution.

Clean all loose plaster from the damaged area and secure the exposed lath with small ring shank nails. If the depth of existing plaster is greater than (on hand) drywall, then add a piece of drywall to the exposed lath with drywall screws, ensure you pre drill all screw holes to avoid cracking the lath. Leaving a 2" space between the existing plaster and the repair piece of drywall. Most doityourself stores carry cutdown pieces of drywall. When you purchase your patch, ensure you buy a piece that is narrower than the lowest spot of your patch. The final coat of joint compound should be at least 1/8 inch above any taped areas.

Feather edge the plaster and drywall with a orbital sander using 40 grit sandpaper. Do NOT break the bond of plaster that has adhered to the back side of the "good" plaster. Clean all surfaces with a vacuum cleaner.
Spray lath and feathered plaster with a light coat of water and apply a thin coat (1/8 in.) of joint compound to all exposed surfaces. Apply 1 layer of drywall tape. Nylon tape works best, however, I have used both paper and nylon. Apply nylon directly to the feathered plaster, lath and feathered drywall, overlapping all strips. (Spray paper tape with water prior to applying to surface.) Apply a second light coat of joint compound to all exposed surfaces. Allow this step to set, but not cure. Apply buildup layers, as needed, until all surfaces are smooth and even. Allow this process to dry until cured. Usually overnight. Joint compound shrinks as it drys so additional build ups may be needed to achieve a smooth, even final patch. Remember to keep all paper/nylon tape at least 1/8 in. below the final surface of your patch.

Sand patch and surrounding plaster smooth. Fill and smooth as needed.

Texture to blend with surrounding plaster.

Joe from Yuma

Answer 4

While the most common answer is "patch it with drywall", it can be done in lathe.

Save the lathe during the demolition. Be very gentle, and use a fine tooth blade on any saw (preferably use a handsaw). Don't stress the old lathe. Now nail the lathe back in place. If you come up short on wood, check a garden store for a cheap trellis to disassemble. You can nail metal lathe over the wood lath, but it's really not needed.

Coat the plaster edges with a concrete bonding agent, or at least spritz them with water (else they'll draw water out of your new plaster and create cracks). Do two coats of "structalite", or another lightweight plaster. Your top coat need not be fully even, because your existing plaster is not fully even.

Now prime. Wait. Prime. Paint.