How should I fill channels left in old plaster after dado rail removal?

Question

I just purchased a condo in the Boston area. The house has been built early 1900s.

I'm removing dado (chair) rails in the dining room that don't look great and are just dust collector at this point.

I used a pry bar to remove one of them and am now wondering how I could patch those holes.

It seems that I am dealing with:

• lath
• Horsehair plaster
• wallpaper 1
• wallpaper 2
• drywall

More pictures

Here is what I think I should do:

Option 1:

• take a piece drywall, screw it to the lath
• dry wall tape + joint compound
• primer + paint

Option 2:

• screw plaster washers on the remaining plaster
• add missing plaster to the lath
• take a piece drywall, screw it all the way to the lat
• dry wall tape + joint compound
• primer + paint

Please advise. Thanks!

Answer 1

As already mentioned, I would use a piece of Sheetrock to fill in. I would add a couple of points:

1. You'll want to use mesh tape on this. Plaster is portland cement based, meaning it likes to absorb water. The mesh tape will hold up better compared to paper tape here. I'd also look for the rot-resistant sheetrock for the same reason.

2. Secure or remove the loose plaster behind the sheetrock before patching. Ideally, it would be best to get the sheetrock to rest only on the lath. I'd even run a bead of construction adhesive between the lath and sheetrock (along with screws).

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For patching plaster, I've used the following procedure with very good success. This assumes good attachment to the lath. If the plaster keys are broken/loose, then that requires some more attention. Crack repair also needs dug out before repairing.

Remove any loose or soft plaster pieces. Vacuum out the area to be repaired. Use something like Elmer's Glue-All and mix 50/50 with water. Using a brush, apply the glue mixture to the old plaster that will be repaired. Again, the reason for this is the plaster likes to absorb water. The glue mixture will help seal the old plaster so that it doesn't take the water from the repair material and also aid in adhesion. Mix up some Durabond 90 for the base patch. Durabond is very strong but it is not intended to be sanded so make sure it is not proud of the finished surface. As a side note, Durabond or other drywall compound that comes in powder form is (almost?) always a setting compound. This means is actually cures like concrete rather than simply dry out like the pre-mixed joint compound. I think it's generally understood that setting compound is stronger than pre-mix. I recommended Durabond 90 as the 90 means it sets in 90 minutes. The longer the set time, the stronger it usually is. Once the Durabond is mixed, try to apply it to the repair area while the glue/water mix is still a little tacky. Allow this to set before applying "sandable" joint compound.

Answer 2

I don't understand option 2, but option 1 is exactly what I'd do. A few suggestions:

• Be sure that the thickness of your drywall brings it to flush or slightly below. Do not install patches that protrude above the wall surface. This will be difficult to tape without leaving a bulge.
• If you end up with a depression after installing the patches, pre-fill before taping, possibly with a setting-type compound (which is more difficult to work with, but cures quickly, is stronger, and doesn't shrink nearly as much).
• Don't worry too much about getting a lot of screws in the drywall patches. The two close tape joints will hold it all very solidly. You don't want to crack up your plaster any more than necessary.
• Use a nice wide knife for your finish coat(s) and taper out substantially. I'd go no less than 12" from the edges of the patch. Skinny repairs will leave noticeable ridges.

Good luck.

Answer 3

I recently had a bunch of plaster repairs done and I would go with option 1 with the following tweaks:

• Use the 'blue board' drywall. I believe this is commonly used in your area.
• Make sure to leave the boards a little shy of the finished surface: not flush.
• Level the wall with something good for plaster repair like Durabond 90.

Using the mud to create the finished surface will make it very similar to the surrounding plaster wall. Layer the mud on in thin layers and let it dry before adding more. There are options that dry faster but since this is your own home, you probably aren't in a huge rush and the extra time will help with finishing.

Take time to finish the mud as best you can with your knife while it's wet. You really don't want to be creating a lot of dust from this by trying to sand it flat. It's not asbestos but it's still not something you want to be breathing a lot of. For the little bit of sanding that is required, got slow with an aggressive grit. Little circles tends to let the dust drop instead of flying in the air.

Answer 4

I would do #1 as well but search for video's on how to tape and bed. Not sure if there is a reason to use plaster in your area or not but we use drywall mud. It is easier to sand and work with. You cannot just fill the void in the joints because they will crack and you will be chasing and fixing cracks the rest of your life or until to rip it out and tape and bed. You will have to float it out about 12" at least to eliminate the bulge of the repaired area. Go slow with several layers until it is all smooth and blended to the existing walls.