Hey all you plaster(ed) guys out there!
I consider myself a good taper/ plasterer, and would like to plaster coat an entire room on an up coming project. You know, covering floor to ceiling in successive coats. I like the look and feel of a well done plaster job. I understand that the guys who do this type of work use the green wall board, rather than the reglar drywall. to suck the moisture up. My question is; what is the “plaster” product to use? Is there a trade name for this stuff, and is it readily available?
Thanks in advance
Robert
Replies
Curious why a good plasterer wouldn't know this...do you only work with 3-coat and mesh?
The board is not the green, but the blue. One product for the veneer finish is Diamond Imperial plaster.
Easysand 90 is a good place to start. Maximum time to work, and less difficult to sand....
-- J.S.
Cloud is right on. "Blueboard and plaster" is the standard wall finish around here (Boston area). Blueboard is hung like any drywall and it is then coated with veneer plaster. Usually, the joints, corners and screws are hit first, and then the whole thing is covered. Before things set up, a texture can be added, or it is troweled smooth. The plastering is all done in one application. It cures to a nice, hard finish and very little sanding is required.
This type of plastering is not something to try the first time on a highly-visible high-value project. You only get one shot, because once the plaster sets up, it's - as they say - set in stone. Practice in a closet or garage. Good plasterers are highly skilled and much in demand. As far as I know, the old three-coat system is not used except possibly in restoration work.
Al Mollitor, Sharon MA
>As far as I know, the old three-coat system is not used except possibly in restoration work.
Or curved walls.
Three coats over your concrete? Are the coats all different types of plaster?
Al
Nah, some of the interior walls. Wood frame, diamond mesh, 2 coats of structo-lite and one of diamond imperial. Too tight a radius (4'-ish) to wanna bend blueboard.
Isn't 3-coat the real plaster? Anything else is either an imitation or a short cut, not?
I personally haven't met anybody who can do three coats. A few year ago the local newspaper reported that there might be about a dozen plasterers in the metropolitan Toronto area that were still doing 3-coat and they were saying it was a dying art. Pity.
We're all dead.
I think for some, even structo-lite is cheating! If it doesn't have horse-hair, it ain't real!! Ha ha ha.
By all accounts, the plasterers here were top-notch. The best were a coupla guys in their later 30's/early 40's. They were teaching a new guy, and after 6 hours of troweling, he was literally ready to cry--that's how badly his shoulder hurt. Both showed signs of hard living. The one died a coupla months later in his sleep at a motel at a job site. 36. 4 kids by 4 women. Hard, hard dude, but we hit it off and when my mom visited one day, he was, "Hello, Mrs. K..." and "Yes ma'am" etc. I missed him on the site when they were done. RIP, Lee.
We're not dead. Plastering is still very much alive, it's just not that prevalent in the residential world. I picked up the trade of plastering when I lived in Brooklyn and worked on the old brownstones. I was in the plasterer's union for a few years working on statehouses, churches and the like, and even did decorative work running mouldings and casting repro's. It's messy work but fun if you like it, plus you get to work on interesting projects. The three coat is still used and veneer plaster can be used as well as the old lime putty and neat process. In residential homes it is mostly used as repair. If you use blueboard and veneer plaster you will have a beautiful plaster finished job...this is the route I would take. Be sure to mesh tape the joints.
When three coat is done now, what do you put it over? I've heard that code doesn't allow the use of wood lath for new work, though it's OK to do repairs over existing wood lath. I had a great plasterer do some repairs for me, and he used two coats over USG RockLath, which is a gyp board with a bumpy surface, sort of like lath and scratch coat.
-- J.S.
I always see it over expanded metal lathe.
Unless you are doing historic conservation and restoration, forget about wood lath. It's part of our past yes, but it is obsolete due to it's properties of weakness, moving around, and it doesn't work as well with the newer harder plasters etc. Gyp lath is fine as a scratch coat although it's not as easy to find anymore. Blueboard is the norm when you are doing a skim white with veneer. Blueboard is basically sheetrock with a paper face that is treated so it bonds with the wet white plaster.
In the three coat method wire lath is what is used, ribbed wire lath is the best for interior if you can find it. In this method you have the first coat which is called the "scratch" coat. This is base plaster which is coarser than the finish plaster and it is mixed with an aggregate, usually sand or perlite. The perlite mix is called simply perlited plaster or the USG brand name of 'Structolite'. It's plaster plain and simple. This first coat is applied over the wire lath just enough to cover the wire and form 'keys' of plaster on the other side of the lath (inside of the wall), which mechanically bonds the wet plaster to the wire lath. Sometimes a strength agent is added to this coat in the form of fibers. Yesteryear it was horse hair, today they are made of fiberglass or strands of plastic. After the plaster is applied and is still wet and pliable on the wall , a scratch comb is run over it forming embedded lines to give the next coat mechanical bonding or 'tooth'. The plaster then hardens (usually 12 to 24 hours.)
The second coat is called the "brown" coat. This coat is meant to build up the wall thickness and level out to a single plane surface on the face of the wall. It is the same plaster mix used as the previous coat except it doesn't contain the fibers. This is the process of "rodding" or "screeding" (as you do in concrete work), and then floating out any bumps with a flat hand float, or a 3 foot long piece of straight wood or aluminum called a "slick". A larger 4 foot float with straight handles on both ends called a "darby" can be used but for some reason it just isn't anymore. The slick has replaced it. This coat hardens.
The third and final coat also called the finish or "white" coat is then applied. There are several different mixes to serve as this but only a few common ones. There is veneer plaster which most people know as the brand name "Diamond" plaster, "Kal Kan" is another. This is simply white gypsum plaster with additives which make it possible to simply mix it with water to the right consistancy and apply. The traditional one for most plasterers is called "gauging" plaster which is mixed with a "slaked" (soaked in water) lime putty in usually a 3 lime to 1 plaster mix, and then applied to the wall in a finishing process too lengthy to go into. The final float is done with a fine wet brush and a quality "honed" (corners knocked down a bit) steel trowel. Plaster is never sanded.
This only scratches the surface (so to speak) of a certain common type of interior plastering. There are hundreds of different finishes, materials, styles, tools etc. It is very much a high skilled trade and has to be taught and practiced and practiced, like most other trades, before one becomes proficient. There's no reason why an average Joe can't give it a try, but find out as much as you can about it and don't expect top notch results the first few times. Timing is everything in plastering, just as the plaster is starting to set knowing when to spatter, trowel and float and especially when to leave it alone. The cool thing about this trade is that not a hell of alot has changed in it's process over the last several thousand or so years. It's very hard work...especially the cielings. It's why I went back to my carpentry.
There are several books on plastering but the plasterer's bible is called "Plastering Skill and Practice" by Van Den Branden and Knowles put out by The American Technical Society. It's the one they teach from in the unions. I think there was a fairly recient printing. Good luck.
Jer: Wow! Thanks for the great overview of plastering!
Al Mollitor, Sharon MA
Over my head? I'm putting in a plaster over expanded metal lath ceiling in the garage using structo-lite (perlited gypsum plaster). Sometimes the plaster comes out white, soft and chalky, most of the time is ends up gray and hard (which is what I think is right) (from the same batch). Why does it come out chalky white? Is this because it was too dry or too thin? Do I need to moisten the first coat when applying the nest coat to prevent it from sucking up too much moisture from the new coat?
Sorry, I don't have a good guess on that chalky white stuff...
There can be a couple of reasons why the plaster is not curing evenly. The plaster itself may be old and may have been sitting around in places where moisture can accumulate thus setting it off (not all of it) right in the bag. The process of making plaster, or portland cement is very basic. A rock, in this case gypsum, is mined from the earth, crushed, pulverized, refined, and then baked or "calcined" so that most of the water is driven out and the structure of the material is different. When water is reintroduced to it, the molecular structure is once again changed and it crystalizes back to a fused state and when mixed with strong agregates it becomes once again a hard rock like substance. Plaster does dry, but it's hardening is due to the crystalization process resulting with an exothermic (giving off heat) reaction. Mix up a cup of plaster of paris with very fast strokes and feel it right after it hardens. Hot baby! Anyhow it's always better to buy your material from a busy store, preferably a mason supply house.
Secondly, it may not be mixed properly or evenly. Structo lite has a fairly long work time so it can really be mixed hard and well. It should be the consistancy of fresh sour cream.
Temperature can affect gypsum plaster as well. It cures better when the air is not too dry and is a comfortable room temp. Cold is not good for gyp plaster.
The scratch coat beneath may be too dry and it is sucking out valuable water in the fresh plaster thus weakening it. If the scratch coat has been left for several days, it may be very dry and needs to be wetted down, not hosed but rather spattered with a masons brush and water. Allow the water to soak into the dry plaster before proceeding. This process is also true between the brown and white coats.
Blueboard and then Diamond or Imperial plaster. Imperial is a harder finish. Neither is sandable. You first skim and then double back. The trick is to get the corners and therefore the whole room done in one shot. Takes 2-3 guys who have specific tasks. The plaster is applied with a trowel rather than a knife used with compound.
You sculpt plaster. Compound you "sculpt" as much or little as you can and then sand the heck out of it. Don't even think you can do this with plaster.
Until you understand the set-up time and the polisheng window of oppertunity don't even take a phone call while applying.
It's great stuff. A real art. Lots of TLC. First try it out on an 8' x 10' wall. Then on two adjacent walls and so on. There are a few dif types of trowels (flexibility). Watch a Pro do it. You'll learn a lot about material body, touch, technique and timing. It's great stuff - especially when tinted.
Have fun.
F.
It is a type of joint compound called "topping compound." It's made specifically for skimcoating. Green board question has me beat.
Thanks to all!
Alot of great info
Although I dont do this type of work for a living, I have come to enjoy plastering in the homes that I've renovated over the years. I think its quite an art, and look forward to working the blue board/ Diamond coat (especially the minimal sanding!). Who knows, if this is indeed a dying art, maybe a new vocation for me.
Thanks again
Robert
Robert,
Next week we'll be featuring an on-line article on plastering written by Sam Singer. He's an accomplished plasterer who makes the task look easy. He talks about taping the joints (use a setting compound so it doesn't absorb the plaster's moisture and become soft), applying a scratch coat, and polishing the lime putty finish coat that doesn't need to be sanded to create a truly monolithic surface. I was impressed with his craftsmanship when I met him, and think you'll get a lot out of his good article.
Best,
James Kidd
Assistant Editor
FHB"I want a good clean fight. No head butts, no rabbit punches, and no hitting below the belt. Break when I say break, and protect yourself at all times."
James,
Thanks for the heads up. I'll check it out next week
Robert