Read through our FAQs to learn about its easy installation, resistance to flame
spread and MoldBlock™ Technology
What subfloor should HardieBacker board be installed over?
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The minimum subfloor specified is 5/8" exterior grade plywood or 23/32" exterior
grade OSB subflooring. HardieBacker board must be installed in accordance with local
building codes and the floor must be engineered not to exceed the L/360 deflection
criteria, including live and dead design loads, for the specific joist spacing used.
HardieBacker board is not designed for use over concrete.
Can I use liquid nails or glue with HardieBacker board?
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No. Where HardieBacker board is being installed over a code-complying subfloor for
the attachment of tile, the board is installed over a 3/32"-1/4" thick bed of bonding
mortar and then nailed down. "Liquid Nails" is not a bonding mortar. It is a structural
adhesive generally used to bond the subfloor to the floor joists just prior to nailing.
It creates a very solid joint between the surface of the floor joist and the subfloor
and aids in reducing floor squeak. The properties of Liquid Nails are such that
it is applied via a tube in the form of a bead-like caulking. It is not trowelable
like a mortar and therefore results in high ridges with unsupported areas that can
deflect under load, resulting in cracked tile.
Where HardieBacker board is being installed directly to wood or metal framing, the
use of a structural adhesive in addition to mechanical fastening can be used. However,
the board must be forced into the structural adhesive almost immediately upon application
to insure that no ridge or crown is formed. The creation of a crown or ridge will
result in an additional thickness of mortar being applied to fill in the valley
created by the crown. This will require a longer curing time and result in a weaker
bond between the tile and the mortar and the underlayment. The use of a structural
adhesive does not result in fewer fasteners being required.
Why can't I get screws to sit flush with the HardieBacker board?
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The screws that you are using do not have the power to rout out the material in
order for the screw head to sit flush. Be sure to use the specified screws (1-1/4"
No.8-18 by 3/8" HD Hi-Lo S or S-12 for metal studs, ribbed phil wafer head, self
drilling, corrosion-resistant screws). If you continue to have difficulties, we
recommend switching to 1-1/4" galvanized roofing nails.
Can HardieBacker 1/4" board be used for floor tile applications?
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Yes, both HardieBacker 500 and 1/4" board may be used for floor tile applications.
If additional height is not required for transition, consider HardieBacker 1/4"
board — which has more compressive and flexural strength than any board on
the market — even when compared to 1/2" glass mesh cement boards. HardieBacker
1/4" 3'x5' EZ Grid® sheet comes with a recessed fastener pattern for even easier
installation.
Can I use HardieBacker board as a fireplace facing?
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Yes, HardieBacker board can be used as a fireplace facing. HardieBacker 1/4" board
can be used as a component in a 1-hour fire resistive construction when installed
in compliance with National Evaluation Report NER-405. HardieBacker boards are recognized
as non-combustible, when tested according to ASTM E 136.