Replies

1. 
   RW | Mar 12, 2003 12:52am | #1

   I'll give you the disclaimer first that I'm not a plasterer and what I know on the subject is little, but sans anything else:

   1. Can veneer plaster be successfully applied to green board as well as blue board? I would suspect it can be applied, results may vary slightly. I think it could since the veneer plaster isn't as dependent on suction as regular plaster is for its bond. Gyp used to be used as a base. Wood and metal lath were waning in popularity, and gyp was in. Incidentally, metal lath is all the plaster and stucco crowd around here use now, as far as I have been able to tell. The local DW warehouse doesn't even stock blueboard.

   2. What is the difference between brown coat and veneer coat? The brown coat is that base that goes on the lath. I can't tell you a whole lot more other than the mix is different for the different layers. cement vs lime vs gypsum etc.

   3. Are there different dry mixes for a base and final coat or do you use the same mix and just keep adding coats? see above

   4. How many coats are typically applied? For veneer, typically one or two. Veneer plaster apparently limits itself to less than 1/8" thickness for practical usage. I would assume going over that causes issues, whether that be cracking or what, . . . ?

   5. Is it acceptable to use pre mixed dry wall mud to finish seams and screw holes before plastering? Thanks for your info! I've heard it's common to use durabond to fill any "oops" areas before the plaster goes on. That seems to jive with my instincts on this, and would make sense since the veneer can't fill large voids and the two products in other usage seem compatible.

   IMHO, not that you asked, if you don't know how to plaster and go read a book on it, thinking that this will teach you what you need, you're in for a world of trouble. I really really wouldn't do it without someone there who knew their stuff. I believe the potential for messing everything up is severe. Nevertheless, hope I helped a little. If you were into reading, Plastering Skills is one I got recently after having it recommended via this forum. Good book, illustrates how much knowlege is really required.

   " Shoot first and inquire afterwards, and if you make mistakes, I will protect you." Hermann Goering to the Prussian police, 1933.

2. 
   RustyNail | Mar 12, 2003 12:56am | #2

   First and foremost, I'm not a plasterer, but have done enough plaster repair to be address your questions...

   1. Can veneer plaster be successfully applied to green board as well as blue board?
   I'd say no, but you should contact USG or National to be sure.  The paper isn't as thick and would not provide the correct adhesion.  If green board is allowed to be used, you'd probably need to use a plaster bonder (like "PlasterWeld") to ensure proper suction of the plaster .  Do not try to veneer on regular drywall, as the moisture in the plaster turns it to mush.  (I learned this once the hard way when someone told me to turn the drywall and plaster on the backside because "the paper's stronger".  They were really wrong, I was really unhappy.) 

   2. What is the difference between brown coat and veneer coat?  Plaster can be done in one, two, or three coats.  Typical plaster today is one coat "veneer" plaster.  This puts about 1/16" to 3/32" coat of finish plaster over blue board.  Two coat and three coat work are found in older houses (my 1940s house has it), and it is thick.  My house has 3/8" gypsum lath, followed by approximately 1/4-3/8" of base coat and 1/8" of finish coat.  Three coat is used especially over metal lath, and the first coat is called the "scratch" coat (because the surface should be scratched to provided "keying" for the second coat), and the second the "brown" coat.

   3. Are there different dry mixes for a base and final coat or do you use the same mix and just keep adding coats?  Different mixes/plasters.  For two coat and three coat the first two coats are usually the same plaster material, though aggregates such as sand may be added in differing amounts between the two mixes.  I typically use USG Red Top Wood Fiber as the base plaster for repairs I've done.  Finish coats would typically be a product like USG Diamond or Imperial.  (FWIW, I'm not partial to USG, it's just what's readily available).

   4. How many coats are typically applied?  Depends how much $ you want to spend.  Typically, only veneer is done in new construction, and it's more prevalent in certain areas of the country (i.e. New England, etc.). 

   5. Is it acceptable to use pre mixed dry wall mud to finish seams and screw holes before plastering? Thanks for your info!  If you're doing veneer plastering, I've read that USG tells you that you can coat the taped seams with Durabond (which is a setting-type joint compound... NOT your average ready-mix out-of-the bucket compound.).  Or, typically the plasterer will just "scratch" these areas first with the finish plaster, then come back over the whole wall.  Again, this is for veneer.  If you're doing the old fashioned two-coat or three coat, the basecoat plaster takes care of any of this. 

   If you want some other information on plastering, try this link to USG's "Construction Handbook", http://www.usg.com/Expert_Advice/const_handbook.asp?menu= and check out chapters 6-8.  They cover veneer and conventional plastering systems, and the products typically used.  It's pretty informative. 

   One last word of warning... plastering is not as easy as they make it look on the TV shows.  You need people helping you to mix up plaster as you're working, and you have to have a feel for when the material is ready to be worked.  For veneer, you apply the plaster, wait until it browns slightly, mist the wall with water, trowel it more, then once it gets almost fully hard, dry trowel it.  It sounds easy, but when you start troweling and the plaster starts "pulling" (kinda scraping off instead of getting smoothed), you begin to realize how much experience is worth.  And... all this assumes that you have good control with the trowel to get it on evenly and semi-smooth in the first place! 

   Good luck, and hope this helps...

3. 
   Clay | Mar 12, 2003 04:14am | #3

   I can tell from your questions that you have a long way to go before you are ready to tackle a project of any size.  Do some research.  Get books from the library or the bookstore, and check the links that I see other posters have sent you.  I have successfully veneered over both greenboard and regular drywall.  I like to use a plaster glue (rewettable) for such applications.  I have heard from top professionals that they sometimes turn the drywall backwards but I have never done it that way.  Brown coats are quite different from finish coats, but for veneering over drywall you don't need a brown coat.  Plan on leaving a bit of trowel marking in your first few walls because true smooth coating is an aquired skill and not a real easy one.  I like a few trowel marks anyway, adds charm and the feel of a hand-tooled surface.  Or you can use a soft trowel (sponge, wood, or carpet) and make a textured surface.

4. 
   Birk | Mar 12, 2003 06:12am | #4

   I am a plasterer with 13 years experience so I'll tell you what I know.As far as going over green board you can do it but I dont reccomend it,its harder to do because it lays wet because the green board is moisture resistant,you just dont get the same job as going over the blue board.Brown coat or conventional plaster which is the correct name is not used as much because of labor time and drying time.With this type of plaster you coat metal lathe rock lathe or even block walls,it can be built up and straight edged off for a straight plumb wall you can actully straighten out any flaws with the brown plaster with a minimum of 1/2" thick. After it sets it can be finish coated with a ivory lime and guaging plaster mix to be trowelled smooth or texured.Vener plaster is 1/16 -1/8 thick can be applied in a one coat or a two coat system,I pre fer the two coat system for a higher quallity job.This is called base coat finish coat system it its a brown coat over the whole board filling in joints and leveling out imperfections in the board after this coat sets the finish coat or white coat is applied.Do not put any joint compound over any board that is to be plastered it is not needed and any good quallified plasterer will tell you this.I would not encourage you to try plastering on your own all you will do is make a mess out of what ever you are doing its not for the weekend warrior you shold call in a qualified plasterer.

1. 
   RustyNail | Mar 13, 2003 12:09am | #5

   Lori,

   About the joint compound...  Personally, I'd scratch any joints with the finish plaster, but USG calls out that joints (for veneer systems) can be treated with a setting joint compound such as Durabond, Easy Sand, or the finish plaster product (Diamond, etc). 

2. 
   GoldenWreckedAngle | Mar 14, 2003 05:28pm | #6

   13 years of plaster experience- just the guy I've been looking for!

   I've been curious about using venetian plaster over the Oriented Strand Board surface of SIPs. I am building a Structural Insulated Panel house and wonder if the inside OSB face of the SIP could be venetian plastered instead of rocked, textured and painted. I mean, I know it can be done- I'm just wondering if it's a good idea, and if so, are there any tricks to plastering over OSB?

   Code requires a minimum of 1/2" of drywall for fire protection on the interior surface of the panels. I am not required to conform to the codes where I am building but I do want to build a safe home for my family.

   As far as I am aware, venetian plaster has not been tested to UL standards for this application. In your professional experience would you be comfortable using it in place of drywall?Kevin Halliburton

   "One machine can do the work of fifty ordinary men. No machine can do the work of one extraordinary man." -Elbert Hubbard-

5. 
   riverr1 | Mar 14, 2003 07:09pm | #7

   Yes you can plaster over the green board. You can also plaster over drywall. A bonder is needed before using either though and it's not going to be as good as the blueboard. The purpose of the blueboard is suction as someone pointed out. Suction refers to the ability of the plaster to stick to a surface.

   The rest of your questions cannot be answered with the information given. I would highly suggest you find a plasterer to do this for you.

   Yes, venetian plaster can be applied to OSB. It really depends on the plaster you want to use to determine how best to go about preping the surface. FYI, starting with the April issue I have a series of articles coming out in Walls and Ceilings Magazine on the tools and how they are used, of Venetian Plastering. These articles will be available on line. Video streaming may also be added. It's being discussed with the web site provider.

   Don