Should I skim coat the old plaster or put on new drywall?

saranyOctober 6, 2008

We are about to start a major renovation on our 1913 colonial revival house. I have learned a ton from this site already. Hope you can help with this problem that's just come up. We've narrowed the choice of GCs down to two companies. They both have excellent reputations,but differ on this one point:

With our old plaster walls, one wants to patch and skim coat, while the other wants to put 1/4" drywall. The rationale for the skim coat is that it leaves a nicer high end finish, while the other guy claims it will crack within 6 months so might as well slap on some new drywall.

What do you think? Any input is appreciated. Thanks!

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I have been doing plaster renovations off and on for a couple years now, in an 1820s house. No, it won't necessarily crack in a couple years. It's helpful to know when the last plaster job was, because you can sort of estimate how long a life a repair is going to have. I have some really trouble spots like over several door frames, and a couple windows. Those openings are not even rectangles anymore, lol, more like trapezoids. They're always going to be shifting. I figure they have withstood nearly two centuries, so likely shall be around for awhile, so I have either fixed them, or plan to eventually. That is, as long as the keys are patent, holding the body of plaster to the lathe.

If you do decide to skim the old plaster, don't take shortcuts. I did on hairline cracks on one side of a door, and put down tape before I repaired the other side. The one repair has lasted, in the other, the crack has shown back up.

I would not cover any plaster in my house, as long as it's repairable........but that is a personal choice I make to keep the house's integrity as long as possible. To me, plaster is a luxury. You expect to invest upkeep in luxuries, just like I keep a tree collection outside. I don't complain when I need to use the services of aborists. It's part of the luxury.

    Bookmark   October 6, 2008 at 3:03PM
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No question, I would do the repairs and skim coating. Even 1/4 wallboard will always be second best in my view and it will disturb the proportions between your wall plane and the protrusion of your trim details.

However, before you do a big round of patching and skim coating, try to analyze why the cracks are there. (I'm ignoring dings and gouges which usually result from single events.) Cracks, from hairline to larger are usually the result of structural stresses, some of which may be recurring. And those will keep reappearing until the issues are resolved. Some hairline and stress cracks are old, and very stable, and won't quickly reappear.

One way to assess this is to mark the most worrisome ones with fine diagonal pencil lines at several points along the crack. Then watch those lines to see if the crack is still moving. If it is, you'll see the pencil lines shift away from each other over time. I regularly do this when a "new" crack suddenly catches my attention. Usually I just haven't seen it before and the pencil line test reveals it's not an active one. A test of at least several months to a year will tell you definitely if you have a real problem, or can safely cover up and ignore the issue. I also write a date next to the lines so I know when I started the test - it reassures me later.

One other thing to keep in mind is that some cracks are the result of seasonal shifts in the house, and nothing (except the unacceptable and unattractive sheetrock solution) will ever "cure" them. These do not portend scary structural issues.

But a great majority of cracks in old houses (at least for the ones that aren't derelict) are the result of long-ago shifts and will be able to be camouflaged with a skilled skim coat.

Beyond, that, perhaps you can persuade yourself to see any recalcitrant cracks (usually just hairlines, anyway) like the owners of a 15c Italian palazzo must see their walls: slightly crazed, but with very good bones!



    Bookmark   October 6, 2008 at 5:33PM
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Christopher Nelson Wallcovering and Painting

Like the others,I would not ruin the integrity of my plaster walls with drywall.

    Bookmark   October 7, 2008 at 5:02AM
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Thanks for your responses. I'm going to do the skim coating like you all suggested.

    Bookmark   October 7, 2008 at 7:48AM
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I see I am preaching to the choir here....but if you wanted a new house with "perfect" walls, why didn't you buy one?
Old plaster, old wood work, old windows....and old people all have certian idiosyncrasies....which I for one love.
Linda C

    Bookmark   October 7, 2008 at 7:50PM
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Agree with keeping the plaster intact and repairing it. As one poster noted, adding drywall will totally throw off the thickness around the trim. You'll have to remove the trim, shave it down and reinstall.

    Bookmark   October 8, 2008 at 11:11PM
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I'm skim coating my old plaster walls currently. If the cracks show up again, easy to re-skim coat.

Also, plaster walls make your interior so very quiet. I can have my stereo up quite loud, and step outside to get the mail and not hear it at all.

    Bookmark   October 14, 2008 at 11:06PM
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I have had some water damange to my plaster ceiling in my bedroom and the person responsible for repairing the damage is the same guy that put on a new roof but forgot to seal the vents. Needless to say, I want to make sure this repair is going to be done properly. Since I have plaster walls and ceilings in my 1920s home, I am concerned with his solution of skimming the ceiling with drywall mud. What will this do to the look of my ceiling and is this proper solution? Thanks!

    Bookmark   October 15, 2008 at 10:51AM
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"I am concerned with his solution of skimming the ceiling with drywall mud"

Drywall premix mud = BAD

Setting type drywall mud (powder in a bag mixed before application) is fine.

Durabond is better, Easysand is for the less skilled.

    Bookmark   October 17, 2008 at 7:39PM
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I'm glad I found this thread! We just bought a 1912 home that has all plaster walls and we have been debating on whether or not to drywall all the walls or to sand down the two or three spots (mostly behind doors) where people have tried to just patch it. We have two main concerns in our house that seem to be different from the ops. #1 We need to be able to get into the walls to run home automation wiring and HVAC ducts. Obviously holes will need to be cut. Concern #2 is our home owners' insurance is almost half again as high because the home has plaster walls instead of drywall (or so they told us when we were initially getting quotes) and that is with the least expensive company. Both of these point to us needing to get some drywall in there but I am afraid the extensive amount of moulding and trim work will never fit properly back into place. I would assume the thickness of a plaster wall could vary all down the wall, so how do you ever make a the trim on a drywall wall fit the way it did on the old wall? Any sugestions would be great, thanks for reading.

Here is a link that might be useful: Dreams & Dust

    Bookmark   October 20, 2008 at 11:41AM
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Huh? That is the first time I ever heard that someones insurance rates were higher because they had plaster and not drywall. That does not make sense to me. If you think about the types of claims that an insurance company would want to minimize such as water damage, mold, etc. plaster comes up superior to drywall.


    Bookmark   October 22, 2008 at 12:03AM
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Sorry, but that is what we were told. The price quoted for plaster was half again what the quote was if we replasted it with drywall. This is our fist home, we have only had to get renter's insurance before and they don't ever ask what kind of walls you have. All I know is what we were told while getting quotes.

    Bookmark   October 23, 2008 at 1:57PM
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I have two properties, both with plaster walls, and the issue has never arisen with my insurance company, either. And, I've never in the decades I have had one or more homes with plaster walls needed to file any claims for them. I have, however, done an "H" of a lot of drywall replacements, on fixemups, where people have run fists, boots, and God knows what through the thin drywall.

I don't disbelieve you, because frankly, it's up to the insurer what they do or don't find's their shot. You implied you have enquired with other companies for quotes. Did they also have penalties for plaster? My kids and I have different insurers, and I know when one of them just bought a new home, theirs made them jump through hoops on certain items. The only thing mine did on an investment house I bought was to ask me to install a handrail on a short set of steps. I would have anyway.

    Bookmark   October 23, 2008 at 10:48PM
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the others were abnormally high, more than double what the PO was paying and they did ask what types of walls when we were going through the questions but only the one (liberty mutual) told us why it was so high implying the walls. They were the last one we contacted and my husband said "WHY is it so high?" and they said it was the plaster walls and that drywall would drop the price of the insurance. We were a little shocked too, I didn't think something like that would matter. Seeing as how we were unfamiliar with the process we figured maybe we just misjudged what was "bad" for insurance and what wasn't. Telling them we were going to run central heat and A/C. removing the boiler didn't affect the price as much as changing to drywall. Maybe the person givingus the quote was crazy, who knows, stranger things have happened. LOL.

    Bookmark   October 24, 2008 at 7:26AM
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Did Liberty Mutual say "why" drywall is considered better than plaster from a risk/payment perspective?

I don't quite get it. I mean, I suppose plaster would suffer more from water damage in a catastrophe, but then you could replace it with drywall if the catastrophe occurs. Does drywall suffer least with fire? Or protect from fire more than plaster? I'd doubt that.

Does it have to do with your replacement insurance coverage choice? I could see that if you have plaster now, and you specify replacement value, then they'd have to payout for replacing plaster and maybe they think that's more cost at payout.

Did they say why plaster was a higher risk to their wallet than drywall?

    Bookmark   October 24, 2008 at 9:58AM
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No he didn't, My husband didn't have it on speaker phone but I was sitting right there and the man was a loud talker so I could hear him speaking. We didn't specify that we would want plaster replacement or anything like that in the event offiling a claim for any reason. Maybe he just assumed. My husband is calling the insurer that the PO was insured with to get his quote and we are going to ask him why they would have quoted higher.

    Bookmark   October 24, 2008 at 3:03PM
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I have older houses with plaster walls.
Normal insurance would replace them with drywall.

It costs more to get a 'same material' policy since plaster is far more expensive to repair and replace.

Another 'gotcha' occurs with foundations following major damage.
You may be required to bring them up to present code.
The insurance for rebuilding old homes with 'same materials' costs more since the expenses of repair are higher.

    Bookmark   October 24, 2008 at 5:59PM
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Yes, it surely would be. Can you see a stately old Victorian being rebuilt with same materials? "Yes, sir, all the radiator covers were Marble." "Yes sir, all the windows are leaded glass". Yes sir, the fireplace surround is art tile and the mantles are solid Mahogany." "Brick facing? Why no, it's triple course construction." Yes, slate roof. "

To be very truthful, our agent told us that many insurers simply drop policies on vintage homes after they've priced them out of sight. He termed them white elephant houses. Ours would limit severely the amount they'd spend to replace our house, and it would not anywhere near be with same materials. It was just understood when we got our policy. I don't think there are craftsmen around who would (or could) build a house to duplicate one this old.

    Bookmark   October 24, 2008 at 8:02PM
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OK, that makes sense that if your insurance specifies "replace with same materials" that the insurance would be higher if the current house has "lath plaster" walls, and they'd be expected to replace the lath plaster walls. That would definitely be more expensive.

But it seems like they could write a tailored policy to state "replace lath plaster with blueboard/plaster walls", so that you're not penalized simply because you're living in an existing house that's older. I mean, I wouldn't go through my house tearing out the lath plaster walls and replacing them with blueboard simply to lower my annual insurance rates.

Good idea to check with the PO and find out what company insured the house previously.

    Bookmark   October 25, 2008 at 2:03PM
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"I don't think there are craftsmen around who would (or could) build a house to duplicate one this old."

They are out there.
Expect to pay for airline tickets and hotels for the duration of the job to get them.

My plasterer died a few years ago (87 years old).
He showed me plenty of tricks in his later years.
He would come and sit at the site and give directions on everything from mixing up the plaster to applying it.

I can do run in place plaster molding, but when he still did the work it was delightful to watch.
He needed help with the horse (the sliding form used to hold the metal plaster pattern) the entire 20 years I new him, but was delightful to work with.

Even molding patterns are still available.
I have done restoration work in Federalist town houses in Alexandria, VA.
Smoot Lumber made some of the original pieces, and is still in business.
It is expensive to have large moldings recreated, but it can be done.

    Bookmark   October 25, 2008 at 5:29PM
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Well, it was probably putting it too strongly. I did find a wonderful wet plasterer several years back to work on my Mama's plaster ceilings. He showed up in snowy painter's coveralls, and I suspect he was in his eighth decade. He brought several other gentlemen with him, also quite mature. I had to laugh, as my mother was afraid for any of them to climb a ladder. But, they were excellent and the price quite modest. I'm sure they did it for the love of their craft, and were a well kept secret in this vicinity.

Let's put it this way. Old, old houses are pretty common here, and extraordinarily unappreciated. They are razed, and cobbled and turned into duplexes by absentee landlords. There hasn't been much of a demand for specialists to work on antique homes, using antique methods. It's hard to even find one anymore who can recognise the old plastering we have, or how our stucco differs from the new latex ones, or how to nail slate. I have found them, but instead of getting more common, the craftsmen are going extinct as they age.

As for the materials, OMG, that's what would kill me. Our foundation is stone. The last listing I have ever seen for a stone cutter, was on the 1870 census. LOL. The house beams are old growth logs. I'd have to win a lottery to ever build a house like this old one, and it's modest and humble. Just constructed like a bunker.

    Bookmark   October 26, 2008 at 12:12AM
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Absolutely not use drywall mud for plaster repair. We repaired all the cracks in our 1910 Colonial Revival and it looks like it did in 1910. We used "Plaster Patch" from Home Depot. It is a lot of work because you have to cut a V-cut all along the crack and then mix a small amount of the plaster patch at a time and apply it to the crack. Then it gets real hot and chemically bonds to the old plaster. It took a long time to do the ceiling and walls of our 6,000 sq. feet house but you really cannot tell where the cracks are now after 11 years. We LOVE our plaster walls!!!!! And no insurance agent has ever mention it cost more to insure. We have our home insured with Chub. They specialize in older homes.

    Bookmark   October 30, 2008 at 11:18PM
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After taking off multiple layers of wallpaper and paint in every room, including all the ceilings, in our 1910 Craftsman, the plaster walls needed to be repaired. The only place we put in drywall was the wall that had to be removed entirely to put in a new main stack. This was 20 years ago and there aren't any cracks so far.

    Bookmark   October 31, 2008 at 12:33AM
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"Absolutely not use drywall mud for plaster repair."

Pre mixed drywal mud (the stuff in the bucket) is a realy bad repair on plaster.

Setting compound (the powder in the bags) is actually a plaster type product and works very well.

I routinely use Durabond for plaster repair.
It is as hard as the original plaster (and sanding messes up the surface).

Easysand can be used if you are not so sure about your ability to work the surface smooth.
It will sand, but is not as hard as plaster (though it is harder than premix mud).

Setting compounds harden by chemical reaction (like plaster) and will not dissolve if they get wet after setting.

    Bookmark   October 31, 2008 at 2:12PM
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Sorry for the hijack...
brickeyee, can a skim coat of plaster be put over painted plaster? If so does it stick as well as it does to unpainted plaster and would I have to remove the paint for a skim coat to be put on?

The guy we had in for some plaster work (does metal lath three coat, and can do crown if we pay him big time, LOL)said he would not recommend putting a skim coat of plaster over painted plaster. He said he could put in a bonding agent, but it doesn't work very well.

    Bookmark   October 31, 2008 at 4:22PM
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The bonding agent is painted on the wall, not mixed into the plaster! And, used in that way, it works very well indeed.

    Bookmark   October 31, 2008 at 11:29PM
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Euco Weld is a popular bonding agent.
It is basically just elmer's glue.

The bonding agent is painted on the surface and allowed to become slightly tacky, than the new plaster is applied.

It works very well when applied and used correctly.

Here is a link that might be useful: Euco Weld

    Bookmark   November 1, 2008 at 11:25AM
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Oh, ok maybe I misunderstood when he explained it to me. Thanks I'll ask him about this and see what he thinks as he is the only true plasterer in my rural area. So once this stuff becomes tacky, regular smooth coat plaster can just be applied normally?

    Bookmark   November 1, 2008 at 5:29PM
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I don't think you can get a nice finish coat directly on top of the bonding agent. At least I had a difficult time, although perhaps a pro would know how. For me, everything slid around too much while you were trying to work it smooth.

My solution was to skim on a mixture of straight plaster and fine sand, with a little durabond in the mix to make it stickier. Apply this as smooth and level as you can to the (tacky) wall surface, feathering down to any trim you aren't removing. It seemed to end up being about 1/8 of an inch thick in most places.

When this sets, you'll have a nice rough surface for applying the putty coat, or whatever finish coat you are using. Whole thing ends up being close to a 1/4 inch thick, though feathered down to an 1/8 or less where needed.

I also had people recommend structo-lite for the rough (bond) coat on painted plaster. I have used that, but ended up preferring the plaster/sand/durabond mixture just on the hunch that it seemed tougher than the structo-lite surface.

I've been very happy with the results, and any subsequent cracking has been very minimal and very fine. (Extensive and heavy cracks and general surface deterioration were the reason for the skim coat in the first place).

    Bookmark   November 3, 2008 at 1:06PM
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When you say straight plaster, what do you mean. Pure gaging? or proprietary "veneer" plaster?

    Bookmark   November 3, 2008 at 9:55PM
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"I don't think you can get a nice finish coat directly on top of the bonding agent. At least I had a difficult time, although perhaps a pro would know how. For me, everything slid around too much while you were trying to work it smooth."

Sounds like you are not leaving enough material on the wall, possibly using too much water in the mix, and did not allow the bonding agent to dry enough.

The layer is about 1/16 to 1.8 inch thick.

The mix for skim coating should be about like peanut butter in consistency. This allows it to be pushed out easily but has enough body to be workable.

Bonding agents need to set up to tacky before applying the plaster. The water in the plaster will help it soften again and grab.

Use of drywall knives also makes covering large areas even more of a chore than it needs to be.

A plasterer's trowel makes short work of covering large areas and produces a smooth finish.
It takes some practice to barealy raise the leading edge to obtain a good finish.
The trowels with the tiny (3/4 inch diameter) handle are not as good as ones with a decent (~1.5 inch) grip diameter.

    Bookmark   November 4, 2008 at 8:48AM
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I used guaging plaster at first, sombreuil, then switched to a product my supplier called "wood fibered", which is basically straight gypsum plaster with some fine wood fibers mixed in. Either one worked fine, but I thought the wood fibers would help reduce any future cracking. It's probably harder to find the wood fibered product - my supplier just happened to have some left over from a big job.

My mix ratio was about 40-45% sand, 40-45% gypsum and 10-20 percent durabond 90. I don't know if you need the durabond, I just used is as extra insurance to make sure by mix stuck to the wall. The bonding agent I applied to the wall first might have been enough.

Brickeyee's comments confirm what I suspected - a more knowledgeable plasterer could probably skip the extra "bond" coat. For an amateur, however, having a nice rough surface to apply the finish coat to makes a challenging job somewhat easier. And I certainly agree that you need a good trowel for plaster work - knives are more for the goopier drywall compounds.

    Bookmark   November 5, 2008 at 1:32PM
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