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achieving a paintable fireplace surround with cement board

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ajmackenzie

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Discussion starter · #1 ·
Hello,

My business is residential renovations and I am receiving conflicting advise on a current issue.

I'm not sure if this belongs here or in the drywall forum.

The job in question was to install a gas fireplace in a new wall. It is a modern looking firepace and the intent was to have it installed in a painted wall without tile surround. ie the appearance of drywall (no tile, or other surrond material). The wall is 2x4 framed, with steel studs immediately around the fireplace per its installation spec. That spec also call fors non combustible clearance 12" above the fireplace- so I cannot bring drywall to the fireplace trim.

So.... we installed cement board on the whole wall ( only 5x8') - using fiberglass tape on the seams and screwing every 8" on studs. We used synco fast set mud (30 and 90 min) and skimmed the whole wall with finishing mud at the end (the fireplace is in a small bump out wall that is 5ft wide by 8ft tall) It all looked good and was primed (zinsser) and painted - almost end of story. 1 week later, 4 cracks are appearing. They start at the fireplace, 2 are at the left and right of the unit (over taped seams), but two huge cracks are developing above the unit and taking off on opposing diagonals - you could put the tip of a ball point pen in the cracks and they are 10" long. (these cracks are not over seams, not out of corners, they are in the middle of nowhere!)

I am preparing to go back and rip it all out and start again. Apparently the CB i used (GreenEBoard) no longer recommends its product for a painted finish only as a backer board. However my supplier did not know this - woe is me. Suffice to say I am looking for a different board. However, I don't want to chalk this all up to the board alone and have it happen again.

My current plan of action is
1) pull off all the board, corner bead etc
2) reinstall 1/2 cement board - rough face out (duroc has been proposed by some folks in my town... although I talked with a CGC sales rep and he said it was not appropriate and had no other recommendations)
3) set all panels tight and use fiberglass, alkali resitant tape set in thinset (first time I used synco tape mud... maybe this is better?)
4) fill coat with synco 30/60/90 mud (i'm told this is better than premixed mud)
5) Skim entire wall for a level 5 finish. prime and paint.

I was hoping some of you could give me your opinion on what may have happened, and what I should ensure on the redo such that this is the end of this story.

Thanks
AJ
 
Discussion starter · #4 ·
ripping was my gut instict... particularly if I can figure out what created the situation so it can be fixed. I just don't want this one to get patched and then it happens again somewhere else on the wall and it keeps haunting me instead of dealing with it once from scratch.

the mud probably ended 1/16 + over the entire surface... but I still can't figure out why it would crack. My suspicision is the substrate (cement board) cracked and I'm just seeing the results telegraphed to the surfaced... but who know til it comes off.

anybody else successfully done this type of finish with duroc or other cement board?
 
#5 ·
Is it possible the greenboard sucked too much liquid out of the mud causing it to crack? I've done similar projects, but using Hardi and skimstone as a finish. If you can chip the mud off, I bet it didn't adhere to the cement board correctly, I think I'd chisel off what I could and prime the surface before applying mud, but then, I hate tear outs.
 
Discussion starter · #7 ·
I'm not sure but I suspect it runs full bore for six hours at a time. You know the story...things get forgot on. Its on a thermostat but that's across the room so it can still get pretty hot.

So anybody see a reason not to use duroc and then mud? Maybe I should prime the duroc with some acrylic first to prevent it pulling too much water out of the mud.... I hate experimenting like this
 
#8 ·
I know it's spendy, but Skimstone really bonds to cement-based boards, and I think it would handle heat better than regular ol' drywall mud. It's pretty fantastic stuff, but IMO it's too soft for what it's designed for (flooring), but not a problem on vertical surfaces, and it looks cool...I hate science experiments on other people's stuff too.
 
Discussion starter · #9 ·
oh boy - did the job again and guess --- what more cracks - I am totally at a loss here. The fireplace isn't even back in and I see cracks in the finish. Owners are away so that rules out any other outside interference. I used a razor and scraped off all compound and the cracks are actually in the duroc.

We put a 4ft high sheet in (no seams) with a small rectangular cutout in the cente of it for the fireplace. The mesh taped seam above failed, and 4 or 5 cracks are apparent... starting at the fireplace cutout and propogating out. Here's a photo. Framing is 16" centers (or less) with metal studs at the opening per the fireplace install spec. Screwed 8" centers.

The only hint of a lead I might have is that we bought the board from outside storage (-10 Celcius) and installed it after leaving it in an unheated garage for only a couple hours. So it is possible this board was barely above freezing and then went in... but I still think that is a long shot. The surface of the board was certainly warm to the touch by install time, and the mud didn't go on for a least a couple hours after it was in the house.
 

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#10 · (Edited)
ajmackenzie said:
oh boy - did the job again and guess --- what more cracks - I am totally at a loss here. The fireplace isn't even back in and I see cracks in the finish. Owners are away so that rules out any other outside interference. I used a razor and scraped off all compound and the cracks are actually in the duroc.

We put a 4ft high sheet in (no seams) with a small rectangular cutout in the cente of it for the fireplace. The mesh taped seam above failed, and 4 or 5 cracks are apparent... starting at the fireplace cutout and propogating out. Here's a photo. Framing is 16" centers (or less) with metal studs at the opening per the fireplace install spec. Screwed 8" centers.

The only hint of a lead I might have is that we bought the board from outside storage (-10 Celcius) and installed it after leaving it in an unheated garage for only a couple hours. So it is possible this board was barely above freezing and then went in... but I still think that is a long shot. The surface of the board was certainly warm to the touch by install time, and the mud didn't go on for a least a couple hours after it was in the house.
Click to expand...
Were you force drying your skimcoats?
 
#11 ·
GPI said:
Were you force drying your skimcoats?
Click to expand...
By a roll of stucco mesh. Like field mesh.
Embed the whole thing with sheetrock.
Your cement board is cracking at the back.
Cement board is notorious for cracking, its very hard to finish simply with mud. I would use a roll of field mesh and mesh the entire thing with sheetrock. Almost like a stucco.
Im doing a stucco application this weekend around a fireplace and im very excited to start it. But thats what we do with stucco.
Mesh it all. That always holds.
 
#12 ·
B.D.R. said:
I recently did this same job. I used hardy backer, full sheet so no seam. Mudded it with general purpose mud. No cracks after a month.
Good luck.
Maybe top mud
Click to expand...
Yep! That would be my recommendation too. I've used the Hardie backerboard for many projects that have been skimmed, textured and painted without any issues what so ever. :thumbsup: Here's a link--> HardieBacker® 500 Cement Board
 
Discussion starter · #13 · (Edited by Moderator)
no force drying on the skim coats. Just ambient basement temp (warm).

Thanks for the Hardie board link - will look into that. Hesitant to go that route if I can make it work without ripping again... HB would entail wripping the whole wall, plus the T Bar profile, removing speakers, etc etc.

So today I sanded back to the durock. Lo and behold there are cracks everywhere. Check out these youtube clips - one from the backside of the wall, one from the front. I checked the framing too - solid, no twisting lumber or anything. The house exhibits no signs of settling/heaving anywhere else, so I am going out on a limb to say the framing is not moving and contributing to this issue.

So I'm going to call the USG rep again tomorrow. The fellow I got on their tech line two days again seemed really knowledgeable - so hopefully with the clips he can chip in some advice. Thus far without seeing it he believes Plaster Bond should be used first on the duroc. Then a coat of diamond interior finish plaster. Then any topping to get it to look good. I'm ok to go this route if he can confirm these micro cracks will be a non issue.

One other local fellow suggested elastomeric paint... my gut instinct is this is a longshot.

Will post back any USG advice I get.

Thanks
 
#15 ·
Ya wow....
Thats pretty brutal cracking...
I honestly just think its bad cement board bro...
I know this one time I installed cement board for a lady's walk-in shower, and whichever store she bought it from I guess would store it outside in the lumber yard, and it must have been sitting in the snow or something. It looked and felt fine by the time it was delivered and dried up in the house. But a few weeks after I installed it, (we just installed the board, didnt finish the tile or anything. We drywalled and taped the house and did the cement board for free as a favor to her.) the cement board to started to crack and even crumble in some spots. And the woman said it just absolutely stunk in her bathroom. Its a good thing she took her time finishing the house because the tile work wasnt done at this point. But still, I had never seen anything like it.
My thinking was it was stored in the snow and maybe it absorbed up some salts which ate away at it from inside.
I've never used cement board since then. Its heavy, dusty, stinks, doesnt cut well and just a pain in the ass. Theres so many different kinds of board now that can replace cement board more effectively and at a cheaper cost that I dont bother with it.

So with all that being said I agree with "Michael Olding."
excessive moisture in the cement board. Perhaps it was improperly stored before you bought it and its acting up now.
Oh and Michael Olding, thanks for agreeing with me ;) lol
 
Discussion starter · #17 ·
Hey folks,

The youtube I just pasted the web address to the specific clip and it inserted as a link. The next time I loaded the page, i found them imbedded as clips rather than just the link.

So for you guys that have done this with with hardie board - can you comment on the steps you used - type of mud for taping (proset or durabond?), skimming, tape mesh or paper? any other criticals to think about. I don't want to ever go back.

Still waiting to hear from the durock tech to see if there is a chance of salvaging the durock or if that needs to come out. aii carumba.
 
#18 ·
if paul says hardiebacker then i'd trust him.
i also like the stucco idea. expanded metal mesh, two coat stucco over top (scratch and finish - use play sand or another fine sand for a better finish) and then prime/paint.
i wouldn't trust elastomeric in this case as it seems like your problems are deeper than that. if it had settled after 10 years and the cracks were small then that's a different story.
 
#19 ·
ajmackenzie said:
Hello,

My business is residential renovations and I am receiving conflicting advise on a current issue.

I'm not sure if this belongs here or in the drywall forum.

The job in question was to install a gas fireplace in a new wall. It is a modern looking firepace and the intent was to have it installed in a painted wall without tile surround. ie the appearance of drywall (no tile, or other surrond material). The wall is 2x4 framed, with steel studs immediately around the fireplace per its installation spec. That spec also call fors non combustible clearance 12" above the fireplace- so I cannot bring drywall to the fireplace trim.

So.... we installed cement board on the whole wall ( only 5x8') - using fiberglass tape on the seams and screwing every 8" on studs. We used synco fast set mud (30 and 90 min) and skimmed the whole wall with finishing mud at the end (the fireplace is in a small bump out wall that is 5ft wide by 8ft tall) It all looked good and was primed (zinsser) and painted - almost end of story. 1 week later, 4 cracks are appearing. They start at the fireplace, 2 are at the left and right of the unit (over taped seams), but two huge cracks are developing above the unit and taking off on opposing diagonals - you could put the tip of a ball point pen in the cracks and they are 10" long. (these cracks are not over seams, not out of corners, they are in the middle of nowhere!)

I am preparing to go back and rip it all out and start again. Apparently the CB i used (GreenEBoard) no longer recommends its product for a painted finish only as a backer board. However my supplier did not know this - woe is me. Suffice to say I am looking for a different board. However, I don't want to chalk this all up to the board alone and have it happen again.

My current plan of action is
1) pull off all the board, corner bead etc
2) reinstall 1/2 cement board - rough face out (duroc has been proposed by some folks in my town... although I talked with a CGC sales rep and he said it was not appropriate and had no other recommendations)
3) set all panels tight and use fiberglass, alkali resitant tape set in thinset (first time I used synco tape mud... maybe this is better?)
4) fill coat with synco 30/60/90 mud (i'm told this is better than premixed mud)
5) Skim entire wall for a level 5 finish. prime and paint.

I was hoping some of you could give me your opinion on what may have happened, and what I should ensure on the redo such that this is the end of this story.

Thanks
AJ
Click to expand...
Did you oversize the pilot holes for the screws for expansion/ contraction?
 
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