# Drywall over plaster considerations



## toomuch (Jan 26, 2010)

This is a bit outside of my scope, but thought I would check-in and see if I need to consider any other variables.

Ceiling in question had some water damage confined to 1 joist cavity. The ceiling seems to consist of a layer of sheetrock/plaster/skimmed with mud/painted with high gloss paint (yellowish layer) then some kind of white textured finish coat. See attached picture. NO LATH or WIRE

Instead of trying to "patch" and considering the multiple substrates. Wanted to simply drywall over the ceiling. Besides accounting for the increased depth and needing to use longer fasteners. Any other things to consider? The finish "texture" seems to be some kind of sand texture and is small enough where it should not interfere with the drywall being directly attached vs having to scrap it down.

joists are 16 oc....

3/8 or 1/2 for the drywall? Any thing else to consider?


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## jlsconstruction (Apr 26, 2011)

Weight 1.9 lbs psqf for half inch. I would never cover up another layer. But then again I'm currently gutting a house with 3 layers and hating every second of it.


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## hdavis (Feb 14, 2012)

That loose stuff is going to be carried by the new drywall. I don't know how you get plaster on a ceiling with no lath.

All the lumps and bumps of the existing ceiling will likely be worse when you put the new drywall up.. Screws tend to punch through the paper when you attach to something like that, or you leave them slightly loose and you get can pops down the line.


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## toomuch (Jan 26, 2010)

The loose stuff is only confined to this one section. Not sure what is ment by "carried by the new drywall". The top layers that are delaminating are only .125 thick in the picture and are most likely a painted sand texture. The picture below is the wall profile of *what I believe was used on the ceiling*. The only difference being the ceiling contains an additional layer with some sort of Perlite or sand texture finish. 

The new layer of drywall would be fastened with screws, through the existing ceiling, into the underside of the joists which are 16 oc so the load of the new drywall would be carried via drywall screws into the joists? Unless I am missing something 

The rest of the ceiling is flat with no humps/waves .........so irregularities transmitting through seem to be minimal. 

As for how the plaster bonds/mends with the sheetrock with no mesh let alone on a ceiling, I have no idea. Has me guessing as well. Perhaps I am not seeing it or this is not truly plaster.

Here is a cross section. Perhaps its not plaster over the drywall and simply some kind of cement board? House was built post WWII late 40's. The drywall is .375 followed by .50 cementous substrate?, finished with .125 skim coat of something

I am no expert on drywall/plaster so any additional comments welcome


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## CarrPainting (Jun 29, 2010)

First off, if the damage in question is just one 'soffit' then why to patch with some mud and call it done?

Why redrywall the whole ceiling?

Second, it looks to me the finish coat let loose of the plates tear. Take a putty knife, and you may find it goes a long way.

Third...

It's probably rock lath... It's like drywall but has a special paper, one coat of base and one coat of finish plaster completes the job...

Rock lath was in direct competition with drywall when drywall forst came out. It's a faster method, delivering similar results. Metal lath and wood lath arnt needed to finish rock lath.

With that said, with out knowing the structual integrity of the ceiling, I would advise against going over it with drywall. Quite strongly infact. If the original ceiling has pulled away and you attach 50+ drywall screws, essentially drilling 50 holes into the surface, if not more, you will substantially weaken the ceiling! Drywall screws won't hold the weight if the ceiling is compromised!

If it is compromised, and you do drywall it, and it looks great, you could have a serious problem if the cieling hits the floor in 6 months, ESP if anyone is in the room! 

My advice, go back and push on the ceiling... If it moves at all, the ceiling is compromised. Well, atleast that section, and NEEDS to be removed. Covering it puts people in physical danger. Not cool

Now... Since your not familiar with this, I would suggest calling someone who is, to atleast guide you thruogh the correct course of action that can do an on site inspection.

By the way your last picture sucks :whistling


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## CarrPainting (Jun 29, 2010)

One more thing, the final layer, that texture part... Remove with a razor scraper. You'll never get the ceiling level, with this type of damage. Patch it with mud. Use a 4' perfectly flat piece of wood called a Darby, or a straight edge, to keep your patch 'square'

Prime with oil.

Touch up

Paint
:thumbsup:


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## bronzgonz (Dec 4, 2012)

Not sure of the name but I call it plaster board. I have cut out the bad section before and replaced with drywall. You might have to shim it where needed. Then tape and finish. For the texture look I have wet down drywall compound and applied it like paint. 1/2" cover and knock it down with a 12" drywall knife. (practice on a scrap piece). Then paint. Did it on a customers house that we have returned to time and again for other projects and after 8yrs it still looks great. We just repainted the room not to long ago and we had a hard time finding the patch.


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## ryanshull (Nov 1, 2012)

yes, rock lathe had a short run, but it isn't at all uncommon, as the economy was booming during the short time they used it.

Another thing to consider is that the ceiling joists may not bear the load correctly without sagging. Sagging leads to bottom layer cracking away from joists which leads to loosening of the top layer and having the screws push through. 

It is hard to tell from my house, but from the pictures, it looks as though you could scrape the skim coat then re- skim and texture.

The texture looks like that cheap sand crap that mixes with paint.

But if that doesn't work, demo the ceiling and start over


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## joethepainter (Dec 1, 2012)

I would tear that out until you get back to solid plaster and patch.

Or I would tear the whole ceiling down and hang drywall.

Or I would fur it out so there was something solid to attach to and it will also help support that cracking plaster that will only get worse with the drywall installation and more time. 

I would not just screw a layer of drywall over that plaster ceiling and sleep under it.


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## toomuch (Jan 26, 2010)

CarrPainting said:


> First off, if the damage in question is just one 'soffit' then why to patch with some mud and call it done?
> 
> Why redrywall the whole ceiling?
> 
> ...


Mr Carr

After doing some googling of "rock lath' you look to have nailed it. Yeah my picture did kind stink but it was the best I could muster. I was able to snap it after the HO had taken off some casing around a door. The plaster or cement section is only .50'' in HO house, but is pretty much the same picture as this (the cement section being larger in the following pic) https://encrypted-tbn3.gstatic.com/...LpFrH5KNHXzVjteB-bM-jxi92aMyrO4TIoXKhx3EY0dNQ

Now that I have an idea what wall system/substrate I'am dealing with I can better understand what the most appropriate fix would be.

Yes overlaying new drywall across the whole ceiling may not be necessary. The 2 main areas of concern are 16 oc joist cavity 10' in length that has the delaminating and some cracking Also a hairline crack exists perpendicular to the joists running apprx 7-8. That being said the ceiling did not "flex" or seem to be detached from the underlying drywall layer or joists. It felt sound.

I think a patch will suffice but will need to inspect closer tomorrow to validate the ceiling is indeed sound.

In terms of repairing "rock lath" cracks. The middle layer (cement looking) ,does this have a name btw, is most likely cracked.

It would be helpful to hear what what type of patch and compound is best to use. That "sand texture" is ugly and the HO suggested a orange peel finish would be acceptable. Can orange peel be applied over a sand textured ceiling, assuming the damaged areas cans be successfully fixed?

This is sounding more and more out of my comfort zone, so will likely bring someone in. However would still like input and suggestions on fixing rock lath cracks to ensure Iam on the same page with whomever I bring in.


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## ryanshull (Nov 1, 2012)

That "cementious" layer is in fact plaster as you thought on the first place. Someone here didn't know what they where talking about - telling you it wasn't or couldn't be.

How loose is that sanded paint? Can you scrape it all off?


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## Big Shoe (Jun 16, 2008)

Just did a bunch of work in a rock lathe/sand texture home. 

It cuts very easily with router or sawzall. Patch with drywall shimmed to match existing. When finishing, make sure you sponge the outer edges (''skitters'') smooth before the compound you use sets up.

And I really found this trick by accident. Too match sand texture I used the oil base Homax orange peel spray in a can with the ''fine'' setting. I was really surprised how good it matched up.

Maybe somebody else will chime in on the true plasterers way to match that sand texture. :thumbsup:

Good luck.


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## ryanshull (Nov 1, 2012)

Big Shoe said:


> Just did a bunch of work in a rock lathe/sand texture home.
> 
> It cuts very easily with router or sawzall. Patch with drywall shimmed to match existing. When finishing, make sure you sponge the outer edges (''skitters'') smooth before the compound you use sets up.
> 
> ...


The texture one there looks like that crap you mix with paint. I'm sure you can find it at just about any paint store.

You used a router? I'm just not seeing that working well.

Your sawzall blade will wear out several times cutting that out, and it will be a crooked mess.

When cutting through plaster, I always pop a line, then use a diamond blade on the grinder to make a nice straight cut through the plaster without chipping it out. Yes, it makes a LOT of dust, but it also makes a nice line to butt new sheetrock up to.

After cutting through the plaster (when its wood lathe) I hammer it off then cut the lathe with whatever saw I need to get in there. With the rock lathe, you might as well go all the way through with the grinder.


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## Inner10 (Mar 12, 2009)

ryanshull said:


> That "cementious" layer is in fact plaster as you thought on the first place. Someone here didn't know what they where talking about - telling you it wasn't or couldn't be.
> 
> How loose is that sanded paint? Can you scrape it all off?


Correct, the cement layer is the brown coat of plaster the hard white is the finish coat. The brown coat likes to crumble all the crap and make a mess and the finish coat likes to crack like ceramic.


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## iDAHOchris (Feb 11, 2012)

If a rehang is acceptible ( overlay) that is what I would do. 16 oc is more than good. Sounds like the house is well built with damage keepping in just on cavity and rest of place is tight as you mentioned. I have done repairs on that stuff before and you end up opening a whole nother can, once that stuff starts cracking....??. Much easier to go over with new rock. Mark out ALL JOISTS correctly , use proper screws ( I would use 4 in the field as opposed to just 3 screws ) and make darn sure they all hit. If weight isnt an issue Id recommend 5/8. Stronger board and it will help to suck it all up good and tight.
If you cant add a layer then when cutting back use as good as a tool you got to cut with ( a grinder works awesome but sure is a mess) that way you dont make more damage. The finish can be rolled on with runny mud and sand


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## toomuch (Jan 26, 2010)

ryanshull said:


> That "cementious" layer is in fact plaster as you thought on the first place. Someone here didn't know what they where talking about - telling you it wasn't or couldn't be.
> 
> How loose is that sanded paint? Can you scrape it all off?


I found a great pic online after doing some more poking around. I am 95% sure this is what I'am dealing with. Not that we havent already figured this out. But the pic I found really shows everything

I have re-attched 2 pictures of the problem areas

2nd photo shows all the layers. Over the cementious layer looks to be some kind of finish layer with a high sheen (yellow in color) Over this is the sand texture (perlite layer) My guess is the sand texture was added well after the ceiling was installed as the textured look became more in vogue.

Ryan as you and others alluded clearly the sand texture layer will need to be scrapped off where its peeling/delimanting. This is issue #1 *Pic#3*

Issue #2 is *where the sand layer and the finish layer* has delimanted from the plaster layer. *Pic #2*

Issue #3 a few hairline cracks exist where it looks like the sand texture, ****** finish layer and the plaster (cementious) layer has a hairline crack.

At this point what Iam most interested is what the appropriate fix is for Issue# 1 2 & 3. Can they be treated the same. Materials/compund to use. For example the hairlines cracks that exist in the cementious layer does that need to be "knifed out" and fiberglass mesh be used with a special compound.

Lastly, can the sand texture be oversprayed with an orange peel texture. The sand texture is ugly, inconsistent and dated. Assuming the problem areas are patchable the entire ceiling would be primed with a BIN Shellac or Gardz before the orange peel was applied. 

Calling all plaster experts!


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## CarrPainting (Jun 29, 2010)

That's deffinately plaster.

It's rock lath with a scratch coat and plaster of Paris and lime.

There's a couple ways to repair this... Here's what *i* would do.

I would check out the intregrety of the ceiling. If I am satisfied at its stability, I would scrape off whats loose, then use my hatchet to chip a more even line around the patch.

Then, I would apply plaster-weld, and apply a new layer of plaster of paris and lime and split my gauge to ensure uniform coverage (it's how I was taught)

Wait a day or so, then prime and paint.. As far as the texture is concerned, your gonna have to try a few things on spare pieces of drywall til you find what's closest. Though I think some of the ideas are close as far as sand mixed with paint. Matching a cheap texture will be difficult.

If they want a smooth surface you could try a small section, by shaving the texture off with a razor scraper, priming with a good thick latex primer such as Glidden gripper, then painting. See how it turns out.

Otherwise you may be stuck with matching the texture, or skimming the whole ceiling.

If your gonna use compound, you can use that crap in the green bucket... And then top coat it with the stuff in the grey and blue bucket called 'dust control'. 

The hair line cracks I wouldn't worry too much about unless they move. Your gonna have to prime the whole ceiling anyways, so hit that crack with little primer and see if it fills in. If it doesn't, then your gonna hafta play with it... In which case, you need a hatchet, and finess to cut out a V in the crack to open it with out breaking it, or breaking the rock lath. Chances are tho, it's at a joint... In which case busting thruogh it could present a more difficult patch to the novice

One last thing...

A rotozip works well for cutting plaster. Sawzalls work good for demo work, and a hatchet works well with not much dust and mess, however in plaster repair work, there will always be dust and debris, and what not, so remember your dust mask, as lime dust is exceptionally toxic. When your nose begins to burn, and you get that funny taste in your mouth, you need a mask!


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## hdavis (Feb 14, 2012)

ryanshull said:


> That "cementious" layer is in fact plaster as you thought on the first place. Someone here didn't know what they where talking about - telling you it wasn't or couldn't be.


Or maybe someone else could use a reading lesson. When I said I didn't know how they got plaster up there with no lath, that's exactly what I meant.

There's probably plaster board somewhere around here, but I've never run into it in 45 years or so.


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## shivers20 (Feb 16, 2009)

I finished a house with the same material on the ceiling, went over it with 1/2 inch drywall, used plenty of screws, its been eight months and still looks great.


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## Big Shoe (Jun 16, 2008)

ryanshull said:


> The texture one there looks like that crap you mix with paint. I'm sure you can find it at just about any paint store.
> 
> You used a router? I'm just not seeing that working well.
> 
> ...


Sorry, but we are talking about two different things here. I can saw through ''sound'' rock lathe with my key hole saw,router and sawzall like a hot knife in butter..........Grinder? I don't think so.

Plaster on wire lathe or wood lathe is a hole nother ball game. Grinder......Yes


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## ryanshull (Nov 1, 2012)

Big Shoe said:


> Sorry, but we are talking about two different things here. I can saw through ''sound'' rock lathe with my key hole saw,router and sawzall like a hot knife in butter..........Grinder? I don't think so.
> 
> Plaster on wire lathe or wood lathe is a hole nother ball game. Grinder......Yes


Yes, but its not just rock lathe, there is plaster on it too. That stuff doesn't hammer off like it does with wood lathe, in my experiences, plaster bonded very well to rock lathe. You fan cut through plaster with whatever tool you choose, but it wears blades or bits very quickly.

When I say the grinder is a dusty mess, I mean it too, so it isn't always the best option, but its always my first choice.


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