# How to patch lath and plaster?



## joecaption (Nov 30, 2011)

1-1/4 seems a bet much.
Cut some 1/2 plywood the width of the hole and about 2" taller then the hole. A simple trick is to use a screw in the middle of the piece as a handle so it does not drop down in the wall.
May have to use a masonery bit with a hammer drill to get through the plaster without cracking it.
A couple layers of 1/2 drywall and a product like Durabond should finish it out.


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## ToolSeeker (Sep 19, 2012)

That seems really thick, thats almost the thickness of a 2x4. As Joe said fill the hole with something solid, then use setting compound to fill, then skim and finish with regular mud.


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## Killavolt (Sep 29, 2015)

I know, it's ridiculous, I don't know why the walls are so thick in some spots.

one of the spots I installed a plug I think is close to 2" thick.

For you guys this seems strange, but the apartment I'm currently living also uses gypsum lath and plaster walls and they also are about 2" thick.

it isn't every wall that's that thick, but it seems that all of the short walls I work on are extremely thick and I don't know why.

I'll take an actual measurement a bit later and you guys can laugh with me at how thick the walls are.


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## ToolSeeker (Sep 19, 2012)

Should be pretty sound-proof.


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## Killavolt (Sep 29, 2015)

ToolSeeker said:


> Should be pretty sound-proof.


it's surprisingly not.


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## ront02769 (Nov 28, 2008)

Where I am there are many pre-war homes.....and many of them have the basic lathe and plaster combo on the walls. This translates to wooden lathe across the studs (at that time primarily wood but moved towards metal later on) so that is a quarter of an inch. Then it gets a scratch coat of plaster which is applied rough, pushing the plaster through the gaps in the lathe, and then the surface is "combed" to make a rough surface which adds 3/8" to the deal. Then a brown coat which is the same mix as the first coat, but this one is left smooth adding yet another 3/8" to things so we are now at a basic inch of thickness give or take a bit depending on the plasterer. This base now gets a final coat of lime plaster....which is approximately 1/8" so assuming everything is perfect you're looking at an inch and an eigth of wall thickness. Guy goes a bit thick on any of the coats, you get up to an inch and a half pretty quickly. Ron


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## MaineLL (Jun 23, 2013)

My method for patching holes in plaster Made for electrical work is as follows. 

1) Make the hole in the plaster larger than the cut plaster. 2-3" larger on all four sides, forming a square. 

2) My top total plaster thickness over the lathe could tend to be thin, so I select 3/8 Sheetrock. It sounds like you may need thicker. 

3) cut that Sheetrock to fill your hole. A small gap is okay around the edges as you'll push the drywall compound in and through the lathes, much as the plaster. Screw the Sheetrock to the lathe. 

4) Using setting type joint compound fill the joint, pushing some through the joint and through the lathe as the plaster was pushed through the lathe. Note that I am not instructing you to tape the joint. I have not had any issues with cracking at the patch. I believe this is because of the combination of screwing to the lathe, the joint compound going through the lathe, and the loose horsehair and plaster edges becoming part of the joint compound. I probably have 3 dozen of these in my house. I added a lot of outlets. 

5) use standard drywall finishing methods to complete. (I occasionally have to do a fair amount of feathering because my plaster leans to the thin side.)


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## Sir MixAlot (Apr 4, 2008)

Put strips of drywall on the studs or furring strips. Then add the right size piece of drywall over that. You can mix the drywall thicknesses to get the right depth.
5/8" + 5/8"= 1 1/4" 
1/2" + 3/8"=7/8" ect...:thumbsup:


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## blackjack (Oct 21, 2015)

Killavolt said:


> I'm no stranger to patching up drywall, but right now I'm dealing with having to cut holes in walls to install outllets and stuff, but the walls I'm dealing with are gypsum lath and plaster, so they are about 1 1/4" thick.
> 
> 
> How can I patch up these holes with a piece of drywall so that the walls are flush, given that the face of the wall is about 1 1/4" off the face of the stud.
> ...


if you're holes are 4" or less then a "california patch" will be fine.
get a piece of 1/2" or 5/8" sheetrock --either will work.
cut a piece that is about 3-4" bigger than your hole (give yourself a little room to learn)
measure your hole and trace a from a template in to the middle of the white side of the sheet rock 
cut the rock from the "white side" to BUT NOT THROUGH to the paper backing.
peel off the excess sheetrock being careful not to rip the brown paper backing
trim off excess rock to fit into the hole you are patching
mix up a little 20 minute "hot mud" (all purpose joint compound will work. I like hot mud because it allows for 2 coats in a shorter period of time.)
apply mud to surrounding area of hole and stick your patch to it.
your brown paper backing should exceed the area of the hole by about 1"-1 1/2"
knife it smooth (not bulging--recessed a little is better than sanding down a bulge) but don't worry too much about perfection. hot mud is more difficult to sand so don't lay it on too heavy, just enough for a first coat.
you can 2nd coat it in an hour or 2 usually. if you're experienced enough to feather (taper) the edges a bit then start doing it with your 2nd coat of hot mud otherwise use all purpose joint compound. it will sand better.
plan on 2 or 3 coats of all purpose and taper out into existing wall usually about 8 inches or so in each direction is sufficient to blend (depending on your level of experience)
don't try to rush it and apply too many coats too quickly it will crack. 1st pass and 2nd pass you can move quickly. beyond that, let it dry. sand a little between coats (again, depending on your level of experience) to remove air bubbles, knife laps and feather the edges (sometimes a wet rag helps with some of the edges depending on the texture you're matching to)
dust off and clean up
texture if needed
clean up
prime
paint 
no more hole.

note: you can use either side of the sheet rock paper. i was just trying to keep the explanation in it's simplest form.


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## Killavolt (Sep 29, 2015)

That's a pretty interesting technique, I didn't know about that before I looked it up just now lol.

My holes are a bit larger though, I was doing some "exploring"


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## Killavolt (Sep 29, 2015)

I measured the thickness and it turns out my estimation skills are horrible lol.

They're just under 1" thick. around 7/8" I think.


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## blackjack (Oct 21, 2015)

5 gallon stir sticks make great 1/4 in backer
I keep loads of them on my van for stuff like this and for stickers, oh and also for stirring paint.sometimes..... 
sir mix a lot has shown the right method for patching them up. ya just gotta figure out how deep you need to back it. I'd use 1/4" stir sticks (cuz they're free and I'm a painter) and 5/8"rock (if your measurement is correct).use 1/2 if you're guessing. you can use screws or liquid nails (i use caulk sometimes) to stick em to the studs and keep a few screws out of the way depending on the shape and size of your holes....i've been behind "explorers" before...lol square up your $#%! holes sparky!  
Happy patching!!


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## ToolSeeker (Sep 19, 2012)

Just a quick reminder to use longer screws 1 1/4" won't be enough.


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## Killavolt (Sep 29, 2015)

blackjack said:


> 5 gallon stir sticks make great 1/4 in backer
> I keep loads of them on my van for stuff like this and for stickers, oh and also for stirring paint.sometimes.....
> sir mix a lot has shown the right method for patching them up. ya just gotta figure out how deep you need to back it. I'd use 1/4" stir sticks (cuz they're free and I'm a painter) and 5/8"rock (if your measurement is correct).use 1/2 if you're guessing. you can use screws or liquid nails (i use caulk sometimes) to stick em to the studs and keep a few screws out of the way depending on the shape and size of your holes....i've been behind "explorers" before...lol square up your $#%! holes sparky!
> Happy patching!!


I cut square holes, I hate when people cut just random shaped holes.

The one tricky spot I have to repair is between to close studs on a corner. There is roughly 3" of space between the two studs, and the wall is cut out flush to the studs.

I may just have to break it off of the stud face and use paint sticks.


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## MrBryan (Apr 28, 2011)

I have had good success using the "California patch" like blackjack described a couple posts up. The nice part is that the thickness of your wall becomes irrelevant since you are latching on to the surface of the wall, not the studs behind it.
I have done a couple about 6"x6" up high on the wall where they will never be disturbed, and I have done a bunch on the lower half of the wall to fill holes about the size of a single gang electrical box. If you end up going this route, mix up some hot mud and it will cure with plenty of strength.

Here is another option - I had another big area about 1x3 feet I had to patch after gutting a bathroom (a large hammer may or may not have gone through the wall during the demo :devil3: ). I patched in a piece of drywall screwed to the studs but I still had about 1/4" difference between the surface of the drywall and the surface of the surrounding plaster. I fixed some metal lath to the patch and built it out with a couple coats of 20 minute hot mud. On this wall the plaster had a texture to it so I would have needed to do something like this anyway to feather out the patch and blend in the texture but it worked out great. With the 20 minute mud it was done in an afternoon and painted next day.


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