Cement board backers are commonly used to cover walls, ceilings and floors over which another type of material will be installed, such as tile or poured cement. The boards create a barrier between the frame or exterior of the area and the new floor, and therefore must be strongly attached in place to prevent shifting or damage later.
Cement Board Screws
To attach cement boards to your fixtures, you must use screws designed specifically for cement board installation. Many cement board manufacturers provide or offer these screws with your purchase; you can also find them at hardware and home improvement retailers. The screws are finished with a special coating that allows them to resist corrosion, which can occur thanks to the alkali levels in the cement of the boards. They also feature small grooves directly under the screw head to allow them to dig into the cement board for better hold.
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If you cannot find or do not have access to cement board screws, there are some types of nails you can use for installing the cement boards. If nails are the way you choose to go, use only galvanized or hot-dipped nails. These types of nails, also used in outdoor decking and roofing installations, have a similar corrosion-resistant coating that allows them to resist rusting or fading from moisture exposure — or, in this case, from the alkali state of the cement board.
Install a fastener every 6 to 8 inches along the perimeter of the boards. In terms of cement board screws, the size of the screw you need will vary depending on the fixture or base to which you attach the board. Cement board attached to plywood or similar underlayment will hold with only 1 1/4-inch screws; for thick or heavy metal fixtures, use 1 5/8-inch screws. In general, 1 1/2-inch galvanized nails will hold the board firmly in place. For flooring or wall installation, some builders choose to apply a thin layer of thinset mortar under the cement board to prevent any shifting or expansion. Even if you use this extra adhesive, you should still apply the nails or screws.
What to Avoid
While cement board may look and feel a lot like drywall or Sheetrock, the makeup of the interior of the boards is completely different. Therefore, drywall screws or nails will not work for cement boards. The fasteners designed for use with drywall do not feature the corrosion- and alkali-resistant coating that enables the cement board or galvanized fasteners to last.