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Plastering over cement board

remodlrj's picture

I'm looking to plaster over the face of a microlam and adjoining portion of a wall.  I have been searching for some plaster (blue) board to install over the beam and planned to apply 2 coat plaster to blend and adhere to the existing lath and plaster.  Only problem is no one around here stocks blue board anymore.  My question to all of you is -  Has anyone ever applied plaster over cement board.  My guess is that it should work but I would like some confirmation.  Are there issues on storing the plaster board?  I thought 2 coat plaster was making a comeback but you need the right board to apply it to, so maybr it's phasing out again.  Thanks for reading this and any input from anyone is greatly appreciated.  

(post #103888, reply #1 of 18)

Here's a little bump...I'd like to know, too.

(post #103888, reply #2 of 18)

I have stucco'd and plastered over it. just make sure you fiber mesh the seams.

(post #103888, reply #9 of 18)

Thanks for the bump and all the posts.  I keep bouncing around in my thoughts on this and am still nervous about the regular drywall/greyboard.  The existing lath and plaster was such a good mix, that I'm hedging towards the cement board w/a sand base veneer plaster and finish coat.  I want this to be as solid as I can make it, without having to go find the sanded base plaster (all I've available is the structolite) and building up a three coat system.(I'm also much better w/ the veneer work.)


Is it feasible to get the veneer base to the right plain as adjacent existing areas (even if it takes two coats) then mesh over the resultant joint and topcoat ?


btw I'm in upstate NY and near Albany and Saratoga,two cities where you would think a fair amount of plastering is going on, but materials are hard to come by.  Suppliers who used to carry them don't anymore.  They all say they can order them but I really don't want to wait.


Thanks for everyone's input!


 

(post #103888, reply #10 of 18)

I wonder how the "paperless" DW would work. I have not used it, but I have heard comments that it is not as smooth as paper faced.

Just some random thoughts.

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(post #103888, reply #11 of 18)

 


Is it feasible to get the veneer base to the right plain as adjacent existing areas (even if it takes two coats) then mesh over the resultant joint and topcoat ?


I'm a little confused by this question, there is no "veneer base", the veneer plaster is applied directly to the blue/grey board.....after you've installed your board, you apply fiberglass mesh tape (self-adhesive), then mud your joints with a setting type compound ( Dura-bond 90 or easy-sand 90 or similiar)  if you need to "build-up" at a joint, then do it with this material to the required level, then apply your veneer coat. The veneer coat  is only supposed to be about  1/8" thick.........maybe this is the "2 coat system you referred to earlier?  


You mention the existing plaster and lathe as being very solid, what is your existing system? I'm  guessing because of the firmness you mention that it's an old 3-coat over wire lath. Is that the case?


 I would stick with the greyboard and paint it with the P-weld if you're concerned then tpae and mud and veneer it, it'll last well beyond our lifetime.


Someone (jer, I think )  mentioned "rock lathe" earlier, could they please define what they call "rock lathe", as far as I know that stuff isn't even made anymore, at least what I know as "rock lathe",......TIA


                                                                Geoff


 

(post #103888, reply #13 of 18)

The two coat system is just a veneer basecoat which has an aggregate for strength applied over the base or blue board or whatever and a smooth finish coat.


As far as I know the rock lath is the old 3/8 thick 16" x ? panals that were plastered over.  

(post #103888, reply #15 of 18)

 


As far as I know the rock lath is the old 3/8 thick 16" x ? panals that were plastered over. 


Yea, that's what I think of for rock lathe..... 16" x 48" drywall is what I'm use to seeing...... this was the transition from wood and/or metal lathe to gyp board.


                                                                                                     Geoff


                                                                                         

(post #103888, reply #14 of 18)

Existing is wood lath and plaster but the plaster is remarkably strong and in good shape.  I've worked around many houses that didn't have walls as solid as these.

(post #103888, reply #12 of 18)

Well I've spent a lot of time trying to get definative answers from manufacturers about plastering over the cement board and I came across the Hardibacker website.  It states that you can finish their backerboard like drywall.  I called them and said that 'sure it's done all the time' and to 'just check with the manufacturer' about suitability for each particular plaster.   


 

(post #103888, reply #3 of 18)

To be safe, I'd apply some PlasterWeld beforehand.  If done with the plasterweld, with joints tapes adequately, I'd think that the plaster would adhere with no issues. 


Oh, and don't try regular drywall for a base for base/finish coat (non-veneer) plaster.  Did it once, it was ugly.  Had mushy drywall/plaster that filled the garbage cans. 

(post #103888, reply #4 of 18)

the Dec 2006 JLC (page 27) has a little article from a plastering pro who says he just veneer plasters right onto regular drywall.  doesn't even use a latex bonding agent.  Says with his and other plasterers "hundreds of thousands of board feet of plaster applied", there's "very little difference" between blueboard and regular drywall !

(post #103888, reply #5 of 18)

As   r  said, you can veneer plaster right over regular drywall with little risk of any failure, the "blue" paper on the board is designed to help the veneer plaster adhere, and keep the board from absorbing to much moisture, to quickly, but I've never had a failure when  going over greyboard, just be sure to "skim" coat it, don't layer it on like some folks do with joint compound,...........


where are you located? ........


also what's the 2 coat system you mentioned?


                                                                                     Geoff

(post #103888, reply #6 of 18)

I'm not a plaster pro, but I will tell you what I think I know. Plaster board is nice if you can find it because it essentially eliminates the need for a scratch coat. But if you can't find it, you could just put up some 15 lb felt and then nail on some diamond mesh. Do a scratch coat to stiffen and then build it up from that point on. No big deal. You could also use drywall, but it would be wise to prime it first with PlasterWeld. Blue board or 'rock lathe' (another version of blue board) has special paper that has tiny particles of gypsum embedded in it... and that's why gypsum adheres so well to it. And yes, there are storage problems with blue board and rock lath... the paper is light sensitive and will degrade if exposed to direct sunlight... The paper turns greenish, which is not good, and that might result in adhesion problems. Not to get nutso, but it might be good to try to match the type of plaster from new to old. If the existing is really old plaster, chances are it's a 'sanded base' plaster rather than a perlite based plaster such as Stucto-Lite. You'd have to mix that type of plaster with sand (doesn't come in a single bag like Structo-Lite) but it's easy. It's my understanding that those two types of plaster (sanded and perlite) have slightly different expansion rates and that joint will be more likely to crack in the future. If you're interested, try Googling Red Top plaster products and you could always call them to find a local distributor.

(post #103888, reply #7 of 18)

I was a member of the Plasterer's Union for some time and blueboard or the traditional three coat on mesh were the norm. On side jobs, the guys would use sheetrock that had been reversed and painted lightly with the P-weld, then the veneer white. It was fine. Not as sturdy and strong as a 3 coat but for residential use it was perfect.
Nothing like a plaster finish.

(post #103888, reply #8 of 18)

 On side jobs, the guys would use sheetrock that had been reversed and painted lightly with the P-weld, then the veneer white. <<<


What does reversing it do? Eliminate the bevel od because of the paper facing?



 


 


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(post #103888, reply #16 of 18)

The backside paper on sheetrock is more porous and has more tooth. But it doesn't matter as much if you use Plasterweld. The guys would just use the backside with no weld and veneer the white on. They taped everything first though. A guaged lime putty finish is the best.

(post #103888, reply #17 of 18)

Well I guess I've come around full circle.  On the USG Website for their diamond basecoat veneer plaster they name their durock cement board as a suitable finish with application of their latex bonding agent (USG Plaster Bonder).  This is the only website or even manufacturer that made that proclamation.  Although some of you had already stated this, I like to be safe rather than sorry.  I'm never afraid to try new things but I do my research beforehand.  that's why this forum is the best!  Always good honest discussions and opinions.  Thanks for all your posts.


Just so you know, USG doesn't make the same claim for their stronger plaster (Imperial).  So what I take from that is not all plasters are equal.  The Diamond is listed as their economical brand.  What it sacrifices in strenghth I guess it makes up for in adhesion.

(post #103888, reply #18 of 18)

I can assure you that Diamond plaster is used over regular, unprimed sheetrock all the time, even on multimillion dollar houses. I have seen it countless times in houses we did timber packages for.