Patching a Large Hole in Plaster Wall

[AdrianeS]

The image below is underneath my sink where the previous homeowner cut a huge out to install the electrical box for the dishwasher and garbage disposal. Obviously there are many problems in this picture.

The electrical box is barely fastened to the stud with one nail at the top that's not all the way in. There is no nail in the bottom of the box, so it's very loose, and there's no wall plate.

What I'd like to do to fix this is patch the entire hole, then cutout a square and install a proper, old-work electrical box, and put a wall plate over the outlets.

The issue is these are old plaster walls and I'm not sure how best to patch the hole. Also, how do I properly route the hoses for the sink and dishwasher through the wall?

Any help is appreciated!

 

[Snoonyb]

So, could you please, step back a few feet an show us a panoramic view of the under sink plumbing connections.

 

[bud16415]

I have done many of these in plaster and lath walls and I will try and describe the method I have found that works best. I always think about taking photos after I’m done.



I buy an old work box of some kind with ears that can take small drywall screws. I then take a small piece of .5” plywood that is 2” on a side larger than the box I’m using. Cut a hole in the plywood so that the box slips in. I then carefully cut the hole in the wall to the size of the box and mark 2” larger around that and carefully remove the plaster leaving the lath. Then put the plywood into the opening and with .5” it should be just below flush with normal old horse hair plaster jobs. If your plaster isn’t that thick use thinner plywood. Run one drywall screw thru the plywood and into each piece of lath. This will strengthen the lath back to better than before you cut it. After the plywood cutout is firmly attached pull your wires into the new box and shove the box into the cutout and screw it in with at least two of the tabs I normally use four. The box should then be pretty close to flush with the wall and if not adjust the tabs or shim for flush. The next step is to tape around the gap between the plaster cut and the plywood with mesh drywall tape and then skim coat the whole area with drywall compound, let dry sand and add more compound as needed dry and finish sand and paint. Reconnect all the electrics and it will look like new.



As to the tubing not sure what you have there and if its code or not. I would handle it off to the side and make some kind of opening with a plate with a hole in it that is removable so in the future you can change or work on the tube.

 

[AdrianeS]

So, could you please, step back a few feet an show us a panoramic view of the under sink plumbing connections.

I didn't see any option to edit the original post so here's another view of under the sink.

 

[AdrianeS]

I have done many of these in plaster and lath walls and I will try and describe the method I have found that works best. I always think about taking photos after I’m done.



I buy an old work box of some kind with ears that can take small drywall screws. I then take a small piece of .5” plywood that is 2” on a side larger than the box I’m using. Cut a hole in the plywood so that the box slips in. I then carefully cut the hole in the wall to the size of the box and mark 2” larger around that and carefully remove the plaster leaving the lath. Then put the plywood into the opening and with .5” it should be just below flush with normal old horse hair plaster jobs. If your plaster isn’t that thick use thinner plywood. Run one drywall screw thru the plywood and into each piece of lath. This will strengthen the lath back to better than before you cut it. After the plywood cutout is firmly attached pull your wires into the new box and shove the box into the cutout and screw it in with at least two of the tabs I normally use four. The box should then be pretty close to flush with the wall and if not adjust the tabs or shim for flush. The next step is to tape around the gap between the plaster cut and the plywood with mesh drywall tape and then skim coat the whole area with drywall compound, let dry sand and add more compound as needed dry and finish sand and paint. Reconnect all the electrics and it will look like new.



As to the tubing not sure what you have there and if its code or not. I would handle it off to the side and make some kind of opening with a plate with a hole in it that is removable so in the future you can change or work on the tube.

Thanks for the advice! However, both the plaster and lath have been completely cutout so I'm not sure your method would work, unless I enlarge the original hole, in the plaster only, enough to where I could then cover the entire space using plywood like you suggested. This sounds like it could work. 1/2" sounds right but I'll have to measure to be sure.

As far as the plumbing, I don't think it's to code. I haven't looked into it, but I believe the plumbing is all supposed to be concealed behind the wall. I still don't know the proper way to feed the pipes and tubes through the wall.

My biggest concern is the electrical box and large hole but if I'm going to fix that, I should probably just take it a step further and feed the plumbing through properly, to code. I'll have to do some research on how to do that.

 

[bud16415]

Correct don't open the hole any larger just cut back the plaster to make a surface to attach the plywood.

When I was rewiring the whole house I made up a pile of these plywood pieces some for a single box and some for a double and having them ready to made it pretty easy.

Everything else I ever tried like clamping boxes and such always ether broke the plaster or got lose over time.

 

[bud16415]

Actually looking at the full photo and it being under the sink if it were mine I would just cut a larger plywood piece with a place for the box and a slot to catch the tube and screw it straight over the plaster screw thru the plaster and into the lath or a stud. Paint it and who cares if it is flush.

 

[Snoonyb]

I didn't see any option to edit the original post so here's another view of under the sink.

Thanks.
I have a slightly different method of correcting this.
Were it I, and assuming the appliance is located in the adjacent cabinet, I would disassemble the DW drain, flex water supply and power cord, then with a hole saw, drill a 2-12" hole in the cabinet wall, just above the floor of the cabinet, where the disconnected DW drain and supply will be run, later.

Next, I would shut off the power that supplies both recep. in the plastic box. Disassemble the recep. from the b ox, and remove the box and replace it with a metal box, which can be secured in place with screws, and are available with or without a plaster ring, because swinging a hammer under a sink, is difficult. Then secure the romex back into the box, without the recep.

Next, because typical gypsum plaster, as applied, is generally 5/8" thick, I would, at the top and bottom of the opening screw and install a 1x3 as backing, clean the plaster from the wood lath on the left side and then install 5/8" drywall. Hot mud will dry quickly so the area can be primed and painted, ready for reassembly, and where the drywall meets the cabinet on the right, caulking can address that.

So, reassembly is all the remains.

View attachment 29914

I didn't see any option to edit the original post so here's another view of under the sink.
View attachment 29914

 

[AdrianeS]

Correct don't open the hole any larger just cut back the plaster to make a surface to attach the plywood.

When I was rewiring the whole house I made up a pile of these plywood pieces some for a single box and some for a double and having them ready to made it pretty easy.

Everything else I ever tried like clamping boxes and such always ether broke the plaster or got lose over time.

Thanks for the tip! This will work I think.

 

[AdrianeS]

Actually looking at the full photo and it being under the sink if it were mine I would just cut a larger plywood piece with a place for the box and a slot to catch the tube and screw it straight over the plaster screw thru the plaster and into the lath or a stud. Paint it and who cares if it is flush.

Good point, nobody is ever going to see it so why bother going to the trouble of cutting it exactly to fit. Thanks again!

 

[AdrianeS]

Thanks.
I have a slightly different method of correcting this.
Were it I, and assuming the appliance is located in the adjacent cabinet, I would disassemble the DW drain, flex water supply and power cord, then with a hole saw, drill a 2-12" hole in the cabinet wall, just above the floor of the cabinet, where the disconnected DW drain and supply will be run, later.

Next, I would shut off the power that supplies both recep. in the plastic box. Disassemble the recep. from the b ox, and remove the box and replace it with a metal box, which can be secured in place with screws, and are available with or without a plaster ring, because swinging a hammer under a sink, is difficult. Then secure the romex back into the box, without the recep.

Next, because typical gypsum plaster, as applied, is generally 5/8" thick, I would, at the top and bottom of the opening screw and install a 1x3 as backing, clean the plaster from the wood lath on the left side and then install 5/8" drywall. Hot mud will dry quickly so the area can be primed and painted, ready for reassembly, and where the drywall meets the cabinet on the right, caulking can address that.

So, reassembly is all the remains.

Thank you, that's another way I could approach this repair. So you would drill a hole in the cabinet wall on the right side of this picture? I've got a few inches of empty space there and then the dishwasher. Would you put anything around the hole (like a large bushing of some sort?) or just leave it bare wood?

 

[Ron Van]

It's hard to tell by the photo but it looks like your P trap arm connects to a flexable hose that goes up. Is that true?



If that is the case, you may want to cut a bigger rectangle out of that wall to fix the plumbing and the electrical before repairing the wall.

The relationship between the P trap and the vent is very important and often goofed up because there is a lot of physics involved. Here's what it should look like.



The trap arm doesn't go up and only slopes down at 1/4" per foot until connecting to the vent with a sanitary Tee (Not a regular tee, combo fitting or Wye).

The P trap/Vent relationship is important to:
1) ensure proper drainage
2) prevent a siphon from forming which will suck the water out of the trap allowing sewer gases into your house.

 

[Snoonyb]

Thank you, that's another way I could approach this repair. So you would drill a hole in the cabinet wall on the right side of this picture? I've got a few inches of empty space there and then the dishwasher. Would you put anything around the hole (like a large bushing of some sort?) or just leave it bare wood?

I generally just allow the drain and cord volume to occupy the boring, but I have seen other things, like insulation or rags or mesh screening.

 

[AdrianeS]

It's hard to tell by the photo but it looks like your P trap arm connects to a flexable hose that goes up. Is that true?

View attachment 29924

If that is the case, you may want to cut a bigger rectangle out of that wall to fix the plumbing and the electrical before repairing the wall.

The relationship between the P trap and the vent is very important and often goofed up because there is a lot of physics involved. Here's what it should look like.

View attachment 29925

The trap arm doesn't go up and only slopes down at 1/4" per foot until connecting to the vent with a sanitary Tee (Not a regular tee, combo fitting or Wye).

The P trap/Vent relationship is important to:
1) ensure proper drainage
2) prevent a siphon from forming which will suck the water out of the trap allowing sewer gases into your house.

Thanks for your input! I posted a side view of the pipes. How exactly would I go about fixing this? I've never done anything with plumbing but I'm definitely happy to learn. Is the trap arm supposed to slope down towards the vent then? It looks like there's less than a foot of pipe for the arm. How do I lay it out to be sloped correctly?

 

[AdrianeS]

I generally just allow the drain and cord volume to occupy the boring, but I have seen other things, like insulation or rags or mesh screening.

I suppose it's fine to leave the hole bare. My mind is just thinking like electrical work where bushings must be used but those pipes won't need any additional protection so might as well keep it simple.

 

[cdestuck]

While you’re twisting and bending under there, if you have any plumbing skills, I’d certainly get rid of your shut off valves and add ball valves.

 

[tomtheelder2020]

Actually looking at the full photo and it being under the sink if it were mine I would just cut a larger plywood piece with a place for the box and a slot to catch the tube and screw it straight over the plaster screw thru the plaster and into the lath or a stud. Paint it and who cares if it is flush.

I like Bud's plan but I would paint the plywood first, both sides and all edges being sure to seal the end grain.

 

[tomtheelder2020]

While you’re twisting and bending under there, if you have any plumbing skills, I’d certainly get rid of your shut off valves and add ball valves.

OP said she doesn't know plumbing. I have twisted a lot of pipe in 30 years as a homeowner but I would not tackle sweating copper. Is this something a newbie could do using a combination of Sharkbite, brass nipples, and PEX?

 

[tomtheelder2020]

I suppose it's fine to leave the hole bare. My mind is just thinking like electrical work where bushings must be used but those pipes won't need any additional protection so might as well keep it simple.

I would fill any gaps, including those where water supply come up into the cabinet, with coarse steel wool. If a rodent should get into your house you don't want to make it too easy for them.

 

[tomtheelder2020]

View attachment 29924

If that is the case, you may want to cut a bigger rectangle out of that wall to fix the plumbing and the electrical before repairing the wall.

Looking at the OP's next photo, I am guessing the pipe coming in from the left of her photo you reproduced is the trap arm for the sink, and that the flex pipe "trap arm" was put in to accommodate the lower outlet from the disposal. Also, it looks like the drain might be iron - and modifying that is a pro job. If she ditches the disposal, is there a simple way to re-plumb this?