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Tying new drywall corner to existing plaster corner

Tying new drywall corner to existing plaster corner

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  #1  
Old 02-17-16, 03:35 PM
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Tying new drywall corner to existing plaster corner

I have a 12-inch high section of wall exposed to the studs at the top of one of our kitchen walls. (There used to be upper cabinet bulkhead in this section.) I need to drywall the exposed studs and merge it with the existing plaster corner that is below it on the rest of the wall. I've tried to draw a sketch of my plan - see pic below.

The main issue is that the existing corner is not square. The existing plaster wall (gypsum lath base, plaster on top) curves in to the corner. Away from the corner the lath+plaster is ~1" thick, but at the corner it's closer to 1/2"-5/8". I'm trying to figure out the best way to get it patched together. I have leftover 1/2" drywall I've been using on other sections that used to be upper cabinet bulkhead. I've been installing it in double layers because it's a close fit with the existing ~1" thick plaster sections. Well, on this corner if I install two sheets over the whole opening then the one corner side will not remotely match with the plaster corner below. As best as I can tell with some various test fits that I've done, the best idea with the materials I have on hand is to put 1/4" plywood over the whole opening, then a second 1/4" plywood layer above the thickest section of the plaster wall. Put 1/2" drywall on top of that second 1/4" plywood layer, and then a separate piece of 1/2" drywall on top of the exposed section of the first 1/4" plywood layer. Put the new corner bead on top of that smaller piece of drywall, and then try to match the lay of the plaster with drywall mud. I'm wondering if this sounds like a feasible plan. I have next to no experience with drywall tape/mud. With this plan the thickest mud area would probably be ~1/4" where the shallower drywall piece meets the farther-out drywall piece and the plaster wall has just started to curve in to the corner. I don't know if this is an issue with any/all mud types. If not, what would be the best type to use?

It's complicated. Hopefully this makes sense for the most part. Further complicating the whole job is that the existing plaster on the opposing side of the corner where it meets the ceiling (only one side of the corner is exposed to the studs) is also not square - it curves out away from the corner as it meets the ceiling. So I have to try to match that somehow with the new corner bead as well.

Ultimately the ceiling is getting covered with 1/2" thick planking, and the wall section being patched will be behind the side of an upper cabinet. It doesn't need to be really fancy, in other words, but I'd still like it to look halfway decent.

In this sketch below, the black lines are the stud walls, red represents the proposed 1/4" plywood, blue is the proposed 1/2" drywall, purple is the proposed new corner bead, and green is the layout of the existing plaster. The non curved side of the corner still has plaster up to the ceiling - except it's cut short of the corner - that's what the hash mark on that line represents. This means the new corner bead doesn't touch the existing plaster on that side. So I'm planning on plugging a slim section of plywood in the gap so the corner bead has something to lay on.

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  #2  
Old 02-17-16, 04:23 PM
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Not sure if I'm completely understanding but why not just shim out the studs as needed and just install the drywall [no plywood]
 
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Old 02-17-16, 04:32 PM
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Have to agree.
No corners are ever 90 deg.
A plaster to sheetrock joint always has to be shimmed to have them come out even.
 
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Old 02-17-16, 04:37 PM
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For some reason, the idea of just shimming the studs never occurred to me. Thanks!

I'll still have the thickness difference for part of the area where the new drywall meets the existing plaster at the curved section. Does it matter what type of mud I use for this?
 
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Old 02-17-16, 09:26 PM
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First, let me say that you will probably be much more sastisfied with the results if you patch the entire corner, not just part of it. Don't know how much of this corner will actually be seen, but it isnt going to look very good if the top 12" is nice and square while the rest looks like it does in your picture. Here is what i'd suggest. After your drywall is installed, put a straight edge on the plaster side of the wall, so that it extends a few feet onto the plaster, and out beyond the corner. Look and see how much mud it would take to fill that void. You could temporarily screw a strip of plywood (onto the drywall side of the wall) so that one edge of the plywood is where you want the corner to be. Once you screw it on, you can use one side of the plywood as a guide, and just fill that void on the corner up with some setting-type joint compound. (Like the 20 minute kind). And like I said, i'd do the whole corner.

Once that is dry, I would then put on a metal reinforced paper tape outside corner... on the entire corner, floor to ceiling. Then finish it as you normally would. The paper corners work great on plaster because you don't have to nail them on (and crack more plaster) you just mud them on and wipe them down tight. You want to square up the corner first, though... using the setting compound I referred to earlier... get it nice and square... then put on the corner bead and finish it.
 
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Old 02-19-16, 07:51 PM
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Since my last reply, I've remembered why I was going to use plywood rather than just shimming the studs. There are only two studs in this section of wall. Thus, I wanted something else to which to attach the smaller section of drywall besides just the right-side stud. I figured the underlying plywood would be better than nothing for an additional screw location.

XSleeper, I like your suggestion of fixing the entire corner. I think I'm going to go that route. I was already a bit concerned about plugging the expected gap between the side of the upper cabinet and the corner, since the wall curves in to the corner on that side. If I square the corner then I won't have to worry about it.
 
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Old 03-07-16, 11:37 AM
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I patched the small wall opening with new drywall, and then put a piece of plywood on the other side of the corner with the edge lined up with the far end of the wall section that was patched. (It's only about a 10-inch section of wall.) In other words, the plywood edge is where the new corner will be. I used 45-minute setting compound over the new drywall up to the plywood and let that dry. I then put plywood the rest of the way down the wall to extend the new corner all the way down. I then used pre-mixed lightweight all purpose joint compound with a 6 inch knife to start building up the corner the rest of the way down the wall. It seemed to go on well, but now that it has dried several cracks have opened up in that first layer. This wall is currently painted plaster (only the small section at the top is new drywall now) and I saw some info online about setting type joint compounds possibly not bonding well with painted plaster, which is why I went with the all purpose joint compound for the rest of the wall. Somewhat fuzzy pictures below.

I'm wondering now if I should have stuck with the setting joint compound for the whole wall (if it's fine to put on top of painted plaster), or if I shouldn't worry about the cracks in the all purpose compound since they'll be covered up by the next layer of compound that I put on. What would be the recommended course of action from this point on?

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  #8  
Old 03-07-16, 02:16 PM
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Ready mix j/c will always crack if it is applied too thick. Because it dries by evaporation it also shrinks causing cracks when it's applied too thick. Setting compounds dry chemically and don't have that problem.
 
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Old 03-07-16, 02:29 PM
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Ok, good to know. So now that I've applied it too thick to start with, should I sand/chip/scrape it off and start over, or leave it alone and use thinner coats for the subsequent layers?
 
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Old 03-07-16, 02:52 PM
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I don't know if it causes any issues down the road. The easiest thing to do is fill in the cracks with j/c.
Generally if we have to build up the compound to any extent we will use a setting compound both because it can be applied thicker and because it dries quicker. I like to use regular pre mixed j/c for the final coat because it is easier to sand.
 
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Old 03-07-16, 04:04 PM
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Yeah that's why I suggested that "You want to square up the corner first, though... using the setting compound I referred to earlier." Then put on the corner bead and finish it.

I would fill the crack with regular joint compound at this point. Lesson learned.
 
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Old 03-19-16, 10:51 AM
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Thank you to each one who's given me advice in this thread! The new corner is just about done and it's looking great! I have the corner bead on with two layers of joint compound so far. I need to sand the second layer and then put one more layer on. Any tips for removing the dust after sanding? I've tried wiping it down with a cloth and also vacuuming it, but I invariably end up with some dust interfering with the next layer going on. Is that just a given of working with joint compound that can't be avoided?
 
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Old 03-19-16, 11:39 AM
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You generally don't sand between coats, unless you have left a ridge somewhere that is too high. Sanding is the last thing you do. Your final sanding may identify a few minor imperfections, and you skim coat just those imperfections with a very thin coat.
 
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Old 03-19-16, 12:19 PM
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Dusting it with an old paint brush or wiping down with a rag should remove the majority of the sanding dust. I always try to apply the j/c in a manner where only the final coat needs sanding. It's best to use a sanding pole or block so you sand evenly, sandpaper in the hand often results in dips.
 
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