HardieBacker® 1/4" board FAQ

Where do I purchase HardieBacker board?

Use the online James Hardie preferred dealer locator or call customer service at 1-888-JHARDIE for your closest sales representative.

How do I cut HardieBacker board?

HardieBacker board may be cut with a carbide-tipped scoring knife, utility knife, or cutting shears (manual, electric or pneumatic).

Where can I get a carbide score and snap knife?

Home Depot® stores and Lowe's Home Improvement Warehouses®.

Which side goes up, smooth or rough?

Either is acceptable, but we recommend that the smooth side with the nailing pattern of every 8" on center go up.

What subfloor should HardieBacker board be installed over?

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.

Why do I have to use thinset between HardieBacker board and the subfloor?

Dry set (ANSI 118.1) or acrylic modified thinset (ANSI 118.4) is specified between the HardieBacker board and the subfloor to eliminate any deviations between our product and the subfloor. This decreases the probability of popping or cracking tiles due to deflection and air pockets.

What do you mean by ''modified thinset''?

The modified thinset used with our product is a fortified cement-based mortar and should specifically conform to ANSI (American National Standards Institute) A 118.4. The thinset can be fortified in a pre-mixed powder form or with a liquid additive.

Can I use liquid nails or glue with HardieBacker board?

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.

What is the correct fastener pattern for installing HardieBacker board?

Fasten HardieBacker sheets with proper nails or screws (as listed in ''Materials Required'' in the backer installation instructions) every 8'' around the perimeter and all supporting studs. Keep fasteners between 3/8'' and 3/4'' from sheet edges and 2'' in from sheet corners.

What type of fastener do you recommend for floor and wall applications of HardieBacker board?

In compliance with the tile industry, James Hardie recommends 1-1/4'' long galvanized or stainless steel roofing nails (0.121'' shank x 3/8'' HD) or 1-1/4'' long corrosion resistant ribbed waferhead screws (No. 8-18 x 3/8'' HD).

Why can't I get screws to sit flush with the HardieBacker board?

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.

Why do I have to tape the joints? What is the purpose of the 2'' wide tape?

The tape will help disperse any movement of the substrate, therefore decreasing the probability of popping or cracking tiles along the seams.

Where can I get the 2'' wide high-strength alkali-resistant glass fiber tape?

Home Depot stores and Lowe's Home Improvement Warehouses.

Can I put HardieBacker board over linoleum or vinyl composite tile?

Yes, Hardiebacker can go over linoleum or vinyl composite tile. Even though you may go over vinyl composite tile, James Hardie does not recommend you install HardieBacker board over cushioned vinyl. Follow HardieBacker floor installation instructions for complete details.

Can HardieBacker 1/4'' board be used in a shower wall application? Is a vapor barrier required?

Yes, HardieBacker 1/4'' cement board may be used in a shower. However, we recommend HardieBacker 500 if you need to make a smooth transition to drywall. The board must be mechanically fastened every 8'' on center to the wood or metal studs spaced a maximum of 16'' on center. A vapor barrier is needed if required by local building codes.

Can HardieBacker 1/4'' board be used for floor tile applications?

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?

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.

Can I use HardieBacker cement board in an exterior application?

In accordance with National Evaluation Service Report NER-405, HardieBacker board is recognized only as an interior substrate.