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mfiore 06-06-2009 11:46 AM

Concrete board
I am doing a walled enclosure around my dome. I plan to frame with steel studs, attach concrete board (Hardie Backer), then face with thin stone veneer.

I've never worked with concrete board before. When putting up panels, do I put them tight together, or leave a small gap (like drywall). If a gap, how large? Do I "mud and tape" the gap with anything before applying the mortar and stone? What's the best way to cut 1/2" Hardiebacker board?

Thanks again for continued advice.

dmun 06-06-2009 11:59 AM

Re: Concrete board
This is a memory from a long time ago, but I remember that the panels are taped with a fiberglass grid material in the shape of drywall tape, and gooped with the same thinset that you apply your finish material with.

And I don't think a gap is called for, since it is just filled with a concrete based material anyway.

wlively 06-06-2009 02:04 PM

Re: Concrete board
Basically, what DMUN said. You need no gap. Make sure and have rough side facing your stonework or stucco.

Easy way to cut is with a carpet or razor knife to deeply score along the line of cut, then overhang cut on a 2x4 or patio edge, ect. and step on it to snap it along the score. The piece will now be hanging by the fiber weave on the unscored side, just cut with the knife.

To make stepped cuts or curves an angle grinder with masonary wheel works well.

Wiley 06-06-2009 02:41 PM

Re: Concrete board
Just to continue.. I prefer Hardibacker as compared to "wonder board" (wonder as in: Why did I buy bought this stuff and not the Hardie Backer?) There are really neat screws for installing the stuff. They are sold under the company name "Buildex" and are called "Rock-On cement board screws". They are hardened and have protusions on the down side of the flat head so they cut their own countersink. They can be used on wood or steel studs. Perhaps the stone veneer you are using is not smooth on the back and that won't matter but I found them really nice when laying tile on the Hardie Backer. Yes, the thickness of thinset does sort of allow for irregularities of round or pan head screws but these screws eliminate catching the notched trowel when spreading the thinset; which I found to be a real plus.

Hope this helps,

mfiore 06-07-2009 07:26 AM

Re: Concrete board
Thanks for the advice. The stone veneer product is to be imbedded into 1/2 inch Type S mortar directly onto the cement board or concrete blocks. No scratch coat needed. Does that mean I should first use the Type S mortar (or thin set?) and the tape to seal the seams, let dry, then apply the veneer with a bed of mortar?

CSWolffe 06-07-2009 08:18 AM

Re: Concrete board
That's not necessary, when you set your veneer, use the type S and tape just before you set your stone. You don't need to let the seams dry first.

Wiley 06-07-2009 09:32 AM

Re: Concrete board
So what does the company that produces the veneer recommend in regards to substrate and preparation? One would expect they want to have successful installations of their product. Perhaps if their website doesn't have answers then a phone call or an email to their customer service division outlining what you are wanting to do would answer any questions.


anilbharti 04-29-2010 04:04 AM

Re: Concrete board
Thanks for sharing this post.

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