Culture Stone over Cementboard Hearth Extension

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  #1  
Old 11-14-16, 01:38 PM
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Culture Stone over Cementboard Hearth Extension

We currently have a fieldstone fireplace and I'm looking to add a hearth extension. I've got a 3'x8' area of exposed plywood in front of the fireplace and my plan is to add a cultured field stone veneer to cover the area and match the existing fireplace. The plan is to screw down 1/2 cement board, add a frame around the area to keep the edges square, lay 1/2" of slab mortar, stick the culture stone down and work it in, and then grout around the next day. My question is, since the stones are laying flat and not hanging on a wall will I get good enough adhesion, without metal lath or a scratch coat, by working the stones into the mortar bed. The OEM instructions for the stone call for cement board and a scratch coat for walls (no lath). But since I'm on a floor retention isn't really an issue. Is the scratch coat necessary? Wondering if anyone has some experience and can enlighten me. I'm trying to keep the surface as thin as possible to keep it level with the surrounding floor. Thanks in advance.
 
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Old 11-14-16, 01:44 PM
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If you need the 1/2" cbu, then so be it. Only 1/4" would normally be required. I don't think the scratch coat with the thick layer of mortar you plan would be necessary, either.
 
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Old 11-14-16, 01:55 PM
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Just to be clear, I'm talking about Type N/Type S stone morter and not thinset. Still think 1/2" is sufficiently thick? Thanks for the quick reply!
 
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Old 11-14-16, 02:29 PM
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how rough are the stones?
 
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Old 11-14-16, 04:25 PM
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Really what you have is a thick tile job. I've laid 2' square cement panels in front of my fireplace right on the sub floor with just a bed of thinset.

I'd use thinset over the mortar!
 
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Old 11-14-16, 05:14 PM
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The stone bottom is pretty rough. Protruding small points.
 
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