I need help with taping plaster to drywall & prep to paint.

11 years ago

Also posted in the Remodeling forum

Hi, I need information on how to tape seams between new dry wall, old unpainted plaster, & painted plaster surfaces in my bathroom remodel. I have a hole to repair too where the old vent stack went out through the ceiling. In the pictures you will see where I peeled off old latex over very old paint from the 40's or so. I wanted to clean up where the taping joints will be. I have not sanded yet but plan to do so.

In reading the other posts on this topic I think it is recommended that I sand the painted ragged edges to smooth, and all over the painted surface to rough it up. Next, wash all painted and plastered surfaces with TSP and rinse well.

Then:

1) do I prime with Gardz, before taping?

2) do I prime the new dry wall too before taping?

3) Do I prime the whole ceiling before I skim coat (if I do this)?

4) How do I handle that hole in the ceiling? (I was going to use scrapes of drywall and mesh to cover, then mud it in place.

5) I bought the low dust blue lid joint compound, will that work for taping corners and ceiling junctions?

Any help would be great!

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Comments (5)

barbcollins
11 years ago
Ugh, I feel you pain. This is what I was dealing with in our recent bathroom. Here is what we did.

We had a whole a little bigger than yours. DH cut a rectangle out and pieced in a larger piece of drywall. I did not prime or paint before taping.

If you are a beginner I highly recommend No Coat for the corners. Yes it's more expensive that regular tape, but gives you nice straight corners with a lot less coats.

I will confess that I gave up on getting the ceiling smooth. I had part plaster, part old drywall, part new drywall. While I know I "could" have gotten it smooth, I was not happy in delaying the bathroom. I did a knockdown texture on the ceiling. It took me less than an hour to do, and you can't see the seems at all now. I did not paint or prime before doing the knockdown.

I don't know about you but I was very happy to see that old ugly cast iron stack gone.
enduring
Original Author
11 years ago
Thanks BarbC. I will even that hole out and start from there. Yes I am so happy to have that pipe gone. It was a bear to clean around. It was kind of cute though. It had a real honest look about it :)
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"I don't think you can get a nice finish coat directly on top of the bonding agent. At least I had a difficult time, although perhaps a pro would know how. For me, everything slid around too much while you were trying to work it smooth." Sounds like you are not leaving enough material on the wall, possibly using too much water in the mix, and did not allow the bonding agent to dry enough. The layer is about 1/16 to 1.8 inch thick. The mix for skim coating should be about like peanut butter in consistency. This allows it to be pushed out easily but has enough body to be workable. Bonding agents need to set up to tacky before applying the plaster. The water in the plaster will help it soften again and grab. Use of drywall knives also makes covering large areas even more of a chore than it needs to be. A plasterer's trowel makes short work of covering large areas and produces a smooth finish. It takes some practice to barealy raise the leading edge to obtain a good finish. The trowels with the tiny (3/4 inch diameter) handle are not as good as ones with a decent (~1.5 inch) grip diameter.
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I did something similar in a place with crazy mixed plasters (some dating back to late 1800's and some from the 30's). We sanded down the highest levels of plaster in the areas that had huge discrepencies in plaster level (yes it's a bit messy, but better than your other options). Then we used venetian plaster for the new wall finishes. That was ten or more years ago when venetian plaster had to be purchased through a high end paint dealer. Now you can buy the stuff by the gallon at home depot and pay for a custom color as well. It's some elbow work to apply, but it will provide a very even finish (you trowel it on and the finish is only limited to the number of layers you're willing to trowel). It's a very old technique, but done in the right colors it's a great modern finish as well. And it's so easy to do. The stuff sticks to just about anything, but if you want to do a test, buy a gallon and practice on a section of your wall. It's VERY important to remember to keep each layer thin as possible. You get cracks when it's too thick, so given the many layers you've got, it may take several layers, but it's not that hard to do. For a more modern finish I'd recommend a pretty wide trowel. Follow instructions, and give it a week to "cure" after you've done at least two, or possibly three coats on your practice section. If you're going to have trouble with it sticking to the old finish you'll see it right away. I personally would pop down a layer of primer before I did anything else, just to seal in anything that might be on those dirty walls :) The plaster finish is hard to get through, but sometimes "stuff" from the old days tries really hard and makes it :) So to be safe, seal it all in and then go for the venetian finish. I highly recommend using a paste wax finish verses the sealer that they sell in the stores. It's basically the same thing, at 1/3 or less the cost, and it's richer. I am picturing a light, silvery or soft green color for some reason, and if you do go light, use a clear paste wax. If you want rich and dark (think chocolate or ebony) then seal the finish with a dark paste wax.
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You say that the drywall is breaking down. It normally won't break down unless it has gotten damp or wet. I think before you cover anything up you should determine if there is a problem. If there is correct if first. The plaster loosening up is fairly common. It could be for a number of reason, but I think you should still be sure that there isn't moisture problem there too. As far as covering the existing walls without removing the old stuff.....I have personlly covered I would guess 40 or 50 rooms and ceilings over the years without tearing out the old stuff. Is there insulation in the walls and will you ever need it there? Celulose can be blown in from the inside and, of course, that would be done first. If the walls aren't in too bad of shape I go over everything with 3/8" drywall and use lots of screws. Where you are going over plaster and lathe you will sometimes hit studs, but often just the lathe. The screws into the lathe will hold as long as you use lots of screws. Over the drywall you will have to locate and hit the studs with screws. Also on going over the drywall, you will have to end the pieces over a stud just as if you were applying it to bare studded walls. If you end it between studs there will be nothing to hold the edges and the job will be ruined. When I go over existing walls I make sure that any wiring that might be needed is done first. If necessary I make holes to run wire. If there are any real uneven spots on the wall I shim out the low spots with scrap pieces of 1/4" or 1/8" luan or paneling. I don't remove the door and window casings or the baseboards. I run the drywall right up against the casing and fill in any gaps with mud when I am taping. Now a lot of remodelers won't agree with going ovre the existing, but I've never had a problem as long as I've used plenty of screws that are long enough to penetrate the drywall or the plaster. If the walls or ceilings are terribly uneven you might have to use 1/2", but I've always used 3/8".
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hags00
11 years ago
First you need to cover the 2 hole. You need to attach the replacement piece of drywall on the big hole to something solid before mudding and taping it. 2 choices are to open up the hole larger until you have some wood to attach it to or improvise! My favorite way to improvise is to cut 1 or two thin boards about 2-3 inches wider than the narrow width of the hole. Stick it up the hole the long way and rotate it so it is resting on top of the hole with about an inch on either side. Hang on to the board in the middle through the hole and put two screws up through the ceiling on either side of the hole to hold the little board in place. Screw your new piece dry wall into the little board(s) you put up there. Tape and mud.

Can't tell how big the little hole I but I would probably jut dry to put a piece of mesh tape over it and mud. If it sags you might need to put something up there to back up that patch too or purchase a firmer patch to go over it.

No need to prime anything until you get all your mudding and sanding done.

Use a putty knife and scrape as much loose paint away as possible. I would do little to no sanding of the paint edges as you are sanding paint with lead. Just skim coat everything with mud.

Patch, tape your corners, mud everything (couple thin coats) and sand. Then prime and paint.

Your joint compound will be perfect for all. Wear a dust mask when you sand.
enduring
Original Author
11 years ago
Hags00, that small hole will be no problem, its smaller than a quarter. I used that picture to illustrate the paint and plaster edges. The larger hole, I think I will use your technique for the larger repair, or a variation of that.

I read some where that plaster did not take well to joint compound. It might have been something about drawing the moisture out of the joint compound too quickly for proper curing of the JC. I believe that was why the Gardz was recommended on the plaster, to provide a surface for taping the two materials at the junctions. Sounds like you haven't had problems with the 2 differing surfaces when taping.
hags00
11 years ago
No I haven't, my current house is plaster and I tore out the soffits and 2 pocket doors in the kitchen and then had to match new drywall to plaster and didn't have any trouble. Good luck with your project!!

I need help with taping plaster to drywall & prep to paint.

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barbcollins

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I need help with taping plaster to drywall & prep to paint.

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barbcollins

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hags00

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