# Repairing peeling skim coat of old plaster?



## mark sr (Jun 13, 2017)

I normally repair plaster with Durabond without using tape. If there is a crack that worries me - I'll use tape.



> Find if I make the area without any original skim too big its hard to get a new layer of even appropriate thickness.


Not sure I understand ??


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## dirtynails (Nov 18, 2012)

mark sr said:


> Not sure I understand ??


If the area where I scraped off the peeling skim coat is bigger than a wide knife or trowel you can't just use the existing edges as thickness guides, you need to float a coat "freehand", which I find much harder, it's difficult to maintain an even coat. I've done more of it recently on other wall defects, but I still hate it. I guess a clean edged piece of lumber will work as a float.


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## mark sr (Jun 13, 2017)

That is a skill you should be able to perfect over time.


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## Gregsoldtruck79 (Dec 21, 2017)

dirtynails said:


> I have a lot of peeling going on in the stairwell of my 100+ year old building. Some actual cracks, but mostly peels. I feel I've made hash of this stuff every time I've attempted it, usually prying off whatever can be pried easily, skimming it with Durabond and then final coats of joint. Should I be taping the transitions? Is there a better methodology? Find if I make the area without any original skim too big its hard to get a new layer of even appropriate thickness.


In my opinion, tape should be used on cracks. I even tape my transition lines (the square cut out in my pic below) from the old to new plaster while using Durabond 90/45. If any plaster is loose or "puffed " outwards, it has to be removed. 

The pic above of the section with the pen appears to me at least, where the plaster has lost its scratch coat bond, and is literally pulling off of the wood lathe. No amount of patching/skimming will last long whenever this happens. Remove and start over time with re-plastering or just remove the old plaster and hang drywall ...is easier and faster some times. JMO


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## joecaption (Nov 30, 2011)

I would have removed all that and sheet rocked over long ago and been done with it once and for all.


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## Gymschu (Dec 12, 2010)

I"m with Joe and Gregsoldtruck on this one. When the plaster gets that bad and is bulging out like that, well, it's pretty much toast. You will spend more time (and money) using up Durabond and regular joint compound to make it all smooth and level again, than you would just tearing it out and hanging new drywall. That plaster looks like an ongoing problem that will vex you every 5 years as it cracks and bulges again, and again.


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## dirtynails (Nov 18, 2012)

Gutting 4 floors of stairwell is a enormous and expensive job. If you've never demoed horsehair on wood, or worse, cement browncoat on metal lath, you haven't lived. Not ready for that! And Greg, the browncoat is not unkeyed, it's just the skim pulling off the brown. 

It's the transition from old skim to new that worries me the most. If it continues to peel it'll just lift off, but taping will buy me more time even though it's a pain to feather out.


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## ClarenceBauer (Mar 4, 2005)

From the photos it looks like the original white coat has an over lay of another white coat which will cause a delamination of the original finish coat to separate from the brown coat due to moisture. For a lasting repair remove all the delaminated finish coating and refinish with a plaster finish do not use a joint compound or a setting compound as they will fail over time due to moisture changes.
You can use a mix mixed finish like USG Diamond or Gold Bong Unical.
For a DIYer your best bet would be to refinish using The Master of Plaster product it would be more user friendly than any other product and will match the existing plaster material.


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## dirtynails (Nov 18, 2012)

Thanks Clarence. In fact, I'd like to hire someone for this who knows how to work with that material as I've got a lot on my plate, but sadly, one needs to be an expert to know whether the "expert" you're hiring actually knows his business. I've been disappointed too many times and had to rip out work and do it myself.


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## Gymschu (Dec 12, 2010)

Wow, I didn't realize you were talking about FOUR floors of damaged plaster. I certainly understand the option of repair rather than replace. ClarenceBauer seems to have the best option for your repairs. Note that the ceiling damage seems to be caused by a possible leak as I see some brown staining where the top layer of plaster has been removed. Best of luck on this one.........certainly NO FUN however you attack it!


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## ClarenceBauer (Mar 4, 2005)

dirtynails said:


> Thanks Clarence. In fact, I'd like to hire someone for this who knows how to work with that material as I've got a lot on my plate, but sadly, one needs to be an expert to know whether the "expert" you're hiring actually knows his business. I've been disappointed too many times and had to rip out work and do it myself.


To find someone who knows plaster maybe very hard. You will need to ask a lot of questions like has he worked on old plaster substrates on wood lath? Does he know the material make up Like your plaster is lime based with sand and horse hair. Does he know what is compatible with that mixture for a good repair? Does he know the steps that were used when it was first applied like scratch coat , Brown Coat & Finish coat. Ask what materials he would use for the repairs? If he states that he would use any drywall materials or setting compounds let him go he does not understand plaster work. Another sign if he is under 55 he most likely wont know how to repair plaster. for the best results check with the local Historical Society they should know of someone to repair plaster or even check with the School of the Building Arts. Also check with the local USG distributor for plaster material sales and who purchased the last plaster materials. When all of the above fail purchase the Manual of Lathing & Plastering and have them follow it.


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## dirtynails (Nov 18, 2012)

Gymschu said:


> Note that the ceiling damage seems to be caused by a possible leak as I see some brown staining where the top layer of plaster has been removed.


Ceiling pics were Greg's, not mine! But I've been there too...


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## miamicuse (Nov 13, 2011)

I have the same problem trying to find a "plaster master" locally. A few I called they don't even know what a rock lath is and I also seem to come to the same conclusion to try and DIY, at least I won't be paying someone to make mistakes.


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## dirtynails (Nov 18, 2012)

miamicuse said:


> I have the same problem trying to find a "plaster master" locally. A few I called they don't even know what a rock lath is and I also seem to come to the same conclusion to try and DIY, at least I won't be paying someone to make mistakes.


I'll bite: what is a rock lath? I can't tell you how many times in my self taught career I didn't know the technical term for stuff, particularly before the internet.


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## ClarenceBauer (Mar 4, 2005)

Rocklath is a plaster board used mostly in the 1930's to the 1950's as a base for a gypsum brown coat plaster application than a white coat finish was applied. The selling point at the time was the board and base coat could be applied on the same day saving two days as related to conventional plaster system. The Rocklath was in bundles 16 inches wide & 48 inches long 6 sheets per bundle. It came in thickness of 3/8 & 1/2 inch. Also came Perforated 3/4 " round holes , Regular & Aluminum foil laminated.


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## mark sr (Jun 13, 2017)

Didn't they do away with the holes a few yrs after the drywall lath came out ???


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## ClarenceBauer (Mar 4, 2005)

mark sr said:


> Didn't they do away with the holes a few yrs after the drywall lath came out ???


The perforated board phased out due to the regular board working so well.
You could order the perforated board if it was required.


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## miamicuse (Nov 13, 2011)

dirtynails said:


> I'll bite: what is a rock lath? I can't tell you how many times in my self taught career I didn't know the technical term for stuff, particularly before the internet.


Haha, I didn't know either. I learned the term from ClarenceBauer here. I didn't know what it was called either, but I have owned two properties built in the 50s with this type of walls and ceilings on them. I have been referring to it previously as a "_three ply wall - a layer of gypsum board, then a layer of stucco like cement material, then a thin layer of white egg shell plaster, with a total thickness of over 1 inch"_, and guys were like "WHAT?":001_unsure:

So after I learned it's called a "Rock Lath" I started to call it that, and guys are still like "WHAT?" :vs_laugh:

It's a real pain to cut holes, or to demo these walls. Lots of dust, and worst of all, is at the corners to another wall or ceiling, they have those wire mesh connections that you have to break out an angle grinder or slowly use a tinsnip to cut off.


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