Stone and tile fireplace hearths often require a backerboard prior to installation.David Sacks/Lifesize/Getty Images
All fireplaces and wood stoves need a solid base to serve as the hearth, not just for the stove itself, but to keep fire hazards from damaging the home. Hearths and stove pads can be built out of a variety of materials, such as brick and concrete or ceramic tile and natural stone, but tile installations first must use underlayment, such as Durock, as a layer between the wood subfloor or the frame of the hearth and the actual tile.
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Encasing a Frame
One way to use Durock is to encase a wooden frame built as the skeleton of the hearth. The material mounts directly to the wooden framing with 1 1/2-inch wood screws. While you can nail the material to the wood frame, it's best to use screws since they hold a grip longer over the years for vertical installations, such as up the face of the hearth. Set the screws every few inches apart. Once the frame is encased completely in Durock, then tile over the installation to finish the hearth.
Over the Subfloor
Durock installed directly on top of the subfloor first must have a layer of thinset mortar troweled onto the surface of the wooden floor to bond with the back of the underlayment. Once the board is mortared down, use 1 1/2-inch roofing nails set every 4 to 6 inches across the face of the Durock to securely fasten the board onto the wet mortar. Ensure you use a thinset mortar rated for use on top of a wooden subfloor, and use a 1/4-inch notched trowel for proper coverage. From there, cover the Durock in tile to finish the hearth.
Thickness and Tips
Although Durock comes in 1/4-inch thickness, in the case of hearths and stove pads where fire and heat are an issue, use the 1/2-inch thickness for proper heat distribution. For best results, combine Durock with thick-bodied tiles such as natural stone to deflect as much heat as possible away from the stove itself. Make sure you leave at least a 1/8-inch gap between pieces of Durock during installation, because the product expands under heat; if there is no expansion room, the Durock will buckle and fold, forcing tiles, bricks and other finish materials off the surface.
If you need to build up a hearth or stove pad to match a surrounding floor, or you just want to add a little extra height, do so with the Durock lining. After you set down your first layer, install another layer on top of the first, nailed down and adhered with mortar. Break up the joints on the second layer, reversing the layout so the two layers don't match up as far as joints go. For example, if you started with a full sheet on the left and cut off at the right, reverse it for the second level of liner. Add other layers as necessary or if desired.