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JUNEBUG 88 02-04-2009 10:49 PM

Slate Hearth
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We are installing for a hearth 1 piece of slate 6' x 18". We were told to use White Flexbond modified polymer. For the Hearth it is made of a frame of 2x4's covered with 2 pieces of 3/4" plywood, ember strip, then 1/2" Durock, then the slate. We needed the frame and plywood to raise the hearth economically. The front of frame will also be covered as well with same materials except no plywood just the Durock and slate.

Question: we have been told various things as to the depth of the cement to use for the slate. Slate place says 3/8" -1/2" flexbond others say 1/4". I would think more cushion is better for more even support is better especially on top, but I am obviously no expert. Do I also need that much flexbond for the front edges that will be under the top slate.
There will be a planned (?) +/-1/2" overhang of the top piece over the edges of the front and side. My brother who has put slate down on his floor will help with cementing and mostly strength.
Any help or suggestions is much apperciated??

Photo is of base unit of hearth without the plywood,Durock or slate.

JUNEBUG 88 02-05-2009 04:26 PM

What no help with slate install?,Thanks

inspectorD 02-06-2009 06:07 AM

I'm trying not to answer all the questions, I would like other folks to get involved somewhat.
The first step is to support the framing underneath. Any blocking installed there is going to help more than anything you do on the top. The top will work fine with some 1/2 inch wonderboard or cement board with whatever bonding mortar you want to use. I would use what the company supplying the stone recommends. Some stone is more porous than others, depends on where it is from sometimes. I would leave a 1 inch finished overhang at the edge, don't forget to add for the thickness of the material underneath.
This should also be inspected by the fire marshal, if you do not , your insurance co. may not protect your assets if there is a problem. This means Fire or carbon monoxide poisoning.
Enjoy your fireplace, it sounds nice.:)

jdougn 02-06-2009 07:39 AM

You are probably aware that the structure underneath keeps the slate from shifting. If the structure has much "give" then cracks appear in your hearth.

InspectorD is right on the lip or overhang. Half an inch is probably not enough. You don't say whether the slate is smooth or textured but it would be very good to increase the lip to accomodate material and installation variation. Also, for your protection and safety get any required permits and inspections.

hth, Doug

JUNEBUG 88 02-06-2009 12:08 PM

Slate is smooth on bottom and slightly textured on top. The carpeting will be cut back and the base will be screwed into the floor and floor joists in numerous areas, it will not move. I am also gluing and screwing the plywood pieces down to the base.
I was planning to leave the structure not connected to the wall so it "flexes" seperately from the wall, or should I connect it to the wall?

JUNEBUG 88 02-06-2009 12:08 PM

Permits are all approved

JUNEBUG 88 02-13-2009 12:05 AM

Passed first inspection unbelievable.
The fireplace has been finally installed and it passed inspection despite all the problems occurring during install. Inspector approved my ideas for the hearth and Marble surround.

I plan to use Hi temp caulk around Marble and hi temp caulk (actually mortar) to seal the gaps around the slate. Looks like another 2 weeks approx. until I get to light the thing.

I installed a z strip sheet metal under the durock. Installers said a strip should have been included with the fireplace, but since instructions weren't I may have thrown it out thinking packing material.
Thank for the suggestions and help!

inspectorD 02-13-2009 06:32 AM

Glad to hear your workin through it, and you passed. Enjoy your fire, you worked hard, did your homework, and pulled permits. You deserve it.:D

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