Hardiebacker is a brand name for a line of fiber cement boards used in construction projects. Fiber cement is a versatile backing material that works well in a number of different applications, including some projects involving fireplaces. This material has strong moisture-resistance capabilities and is also heat resistant, making it an ideal liner for projects around your fireplace.
Using Hardiebacker on Fireplaces
You can use Hardiebacker board around your fireplace. However, there is a key difference between "around" and "on." Your fireplace footing is made from masonry material that needs to remain in place. It cannot be replaced and should not be covered up with more flammable materials. However, using fiber cement board like Hardieboard is acceptable in locations including the mantel and fireplace surround.
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Fire Ratings
The Hardiebacker board is made with a quarter-inch thickness so that it can serve as fireplace facing. It can be used as part of a hour-long fire wall, which is a wall that can resist a fire for up to an hour when properly constructed. Hardiebacker board is generally noncombustible, and the heat produced from the fireplace will not damage it.
Uses
Hardiebacker board is not designed to take the place of stone, drywall or other materials used near or on your fireplace. Instead, it was designed to be a subfloor or backing material for another material installed on top of it. Around a fireplace, you can use Hardiebacker board to prepare an area for tile installation, either stone or ceramic.
Cutting and Caulking
When fitting Hardiebacker board, cut the fit very carefully, using high-powered shears or carbide-tipped scoring knives to make proper cuts. To improve structural integrity, do not align the cement board with any plywood joists. To maintain the fire-resistance of the wall you are working on, use fire caulk that is designed to provide similar protection to the board itself.