Replies

1. 
   mike4244 | Jun 29, 2003 09:23pm | #1

   Plastering over blue board ( drywall specifically for white coat of plaster) is done all the time. If the drywall is regular drywall, I would contact Gypsum board manufacturers ,ask them. If the plaster that is on now seems ok except for the finish, you should be fine.

1. 
   paulc127 | Jun 29, 2003 11:19pm | #2

   Thanks for your reply. As far as I can tell it's regular drywall. The Gypsum Mfg. site says no in their FAQ's but two plaster contractors have said it's okay. I assume they'll nail metal lathe or something to help the plaster adhere. I just not sure any of this is a good idea. MaybeI just need to learn to like skip trowling.

1. 
   mike4244 | Jun 30, 2003 12:07am | #3

   I doubt that the plaster will nail metal lath on the drywall. If he does, he will need more coats of plaster. When plaster is troweled on blue board only a white gauging coat is applied. I am inclined to go along with what the plasterer wants to do. I have seen plaster over drywall, but this was a demonstration at a masonry supply house.  Blue board was not available for this demonstration. The sample was displayed for several months, still looked fine when they threw it out.

   Mike

2. 
   RW | Jun 30, 2003 12:19am | #4

   You'll be fine. If you can't find blueboard for a plaster skim coat job, hang regular rock and coat it with bonding adhesive. On your wall, grab a 5 gal of the stuff and a thick nap roller. An hour later, plaster away.

   "The child is grown / The dream is gone / And I have become / Comfortably numb "      lyrics by Roger Waters

3. 
   Piffin | Jun 30, 2003 01:06am | #5

   I've done it for patch jobs and never a problem. I prime with bonding agent first and trowel on.

   The only bad thing I can imagine is that the substrate (sheetrock) is not as dense as the plaster finish or as blueboard, but the old horsehair plaster was pretty soft too.

   .

   Excellence is its own reward!

1. 
   rez | Jun 30, 2003 03:36am | #6

   Piffin-

   Would you prime with a bonding agent first if freshening up an old wall of drywall with a texture coating of drywall mud?

    

    

1. 
   Piffin | Jun 30, 2003 04:32am | #7

   Yes.

   Your old rough texture grants you a mechanical bond but adding the chemical bond is a plus.

   The other thing it does though is to seal the wall so it doesn't suck moisture out of the mud while it is curing..

   Excellence is its own reward!

1. 
   rez | Jun 30, 2003 04:37am | #8

   Thanks. What would be a reccommended bonding agent?

    

    

1. 
   Piffin | Jun 30, 2003 05:00am | #9

   I go in and see what's on the shelf. Acryl 60 comes to mind. They all look like a white glue, or grout additive, thinned to paint consistancy..

   Excellence is its own reward!

2. 
   rez | Jun 30, 2003 05:08am | #10

   ^

    

    

3. 
   riverr1 | Jul 02, 2003 07:35am | #11

   The best bonder available is larsen's plaster weld. It is useable for days where the others are hours. When plastering over an existing texture, make sure to trowel like you would float over grout. Hit it from all directions to key the plaster to the texture. Any voids are potential problems.

   Thought I responded to this earlier, but I don't see it now??????

   Don

4. 
   DennisS | Jul 02, 2003 11:39am | #12

   I don't think it's an issue of *if* it can be done as to *how* it will be done.

   Several of the respondents have mentioned plastering over blue board (genuine plaster base material). This is not gypsum drywall or wall board. It's intended to accept finish plaster materials. Drywall isn't. You say you have an existing skip troweled finish on your walls. Is it painted? I have a light orange peel finish on a house I'm remodeling and asked my drywall finisher what it would take to trowel it all out to smooth wall. He said (since it's been painted) you end up with little blisters trying to skim coat over the texture.

   Unless your plastering contractors intend to treat the surface somehow to provide proper adhesion, I would have reservations about putting a veneer plaster finish on an existing painted gypsum board surface.

   ...........

   Dennis in Bellevue WA

   [email protected]

1. 
   riverr1 | Jul 02, 2003 05:20pm | #13

   Dennis,

   Ala the bonder. Actually, I wouldn't worry about bubbling with the plaster anyway. The application of plaster is very different then mud. Once the plaster begins to set, you go back and hard or back trowel the finish. Can't do that with mud unless you want one mell of a hess.

   The blue boarddrywall suggestions are a bit of a non issue since this is an existing finish as you've pointed out. Besides, many plasterers don't bother with blue board anyway. The only difference between the two is the paper. Blue board has what's called better suction. When using a bonder it becomes another non issue to many plasterers. If I were to use blue board, I'd have to drive 30 miles to get it, and most don't stock the stuff in drywall sizes anyway. Most stick to 8 and 12 footers. That's not economical.

   Don

5. 
   RustyNail | Jul 02, 2003 10:28pm | #14

   A couple approaches I've taken with success:

   1.  PlasterWeld, followed by either USG Diamond Plaster or USG Durabond or EasySand joint compound. 

   2.  Prime with oil-based primer, then USG Durabond or EasySand. 

   I tend to prefer using Durabond over actual finish plaster, just as it's what I'm most familiar working with.  The suggestion for oil-based primer comes into play when the paint on your wall is questionable.  I've had some absolutely horrible experiences when I skim-coated walls with joint compound only to watch the paint underneath bubble off. 

   In any event my recommendation is to put your coats on thin, and to use either plaster or setting-type joint compound mentioned above.  When doing this work, I've found moisture to be my enemy, so the longer the finish stays wet, the more likely the paint underneath bubbles or the drywall underneath becomes a soft spongy mess.