Tile Backer Board for Floors and Showers

Tile backer board gives your floor, shower wall or countertop a surface made for bonding tile. Durock cement board with EdgeGuard is water-durable, and James Hardie HardieBacker resists moisture damage. That’s the foundation to buy for a bathroom remodel or a Montana mudroom where snow melts off boots.

The buying decision starts with the surface underneath, how wet the room gets and the thickness your finished tile needs. Get those three right before choosing the board.

Cement backer board for tile floors

Cement backer board, also called cement board, goes over a structurally sound wood-framed subfloor to provide the underlayment for tile. Both 1/4-inch and 1/2-inch cement backer board can be used on floors. Quarter-inch board usually makes floor transitions easier to match. Buy thickness for the finished floor height, not for extra structural strength.

Cement board does not stiffen a floor. Settle the support underneath first, then put down the tile backer. A thicker panel is no cure for a floor that moves.

Winter is interior renovation season in Montana. When you’re replacing a bathroom or kitchen floor in an older house, the open subfloor is your chance to address loose or damaged material before covering it. Give the board sound support and it can do the job you’re buying it for.

Durock cement board with EdgeGuard for showers and tub surrounds

Durock Brand Cement Board with EdgeGuard is a water-durable tile backer for floors, walls, countertops, and tub and shower areas. Buy it for a shower surround where resistance to water damage matters every day.

Is cement backer board waterproof? Water durability does not make the shower assembly waterproof. Ordinary cement board needs additional waterproofing in showers, and tile and grout are not waterproof either. Buy the board and compatible waterproofing together so the moisture protection is part of the job from the start.

To waterproof cement backer board, use a compatible membrane or coating as part of the shower assembly. Carry the waterproofing through seams, corners, penetrations and fastener locations. Those details matter even with a board that has built-in waterproofing. Taping a board joint with thinset prepares the joint; it does not replace shower waterproofing.

Durock Tile Backer Screws are a fastening choice for Durock with EdgeGuard. Buy backer board screws matched to the board instead of using leftover fasteners. Too few fasteners or heads driven too deep can spoil the installation.

For exterior cement backer board work, Durock with EdgeGuard also has exterior finish-system applications. Choose an assembly recommended and warranted for the particular exterior finish. Montana freeze-thaw exposure makes that a separate decision from choosing a board for an indoor shower.

Ordinary drywall and water-resistant drywall are distinct from tile backer board; keep them separate when choosing the backing for your tile job.

Glass-mat water-resistant gypsum backer board

Glass-mat gypsum backer board has fiberglass reinforcement on both faces. The distinction to keep straight is coated versus other glass-mat board: coated glass-mat water-resistant gypsum backer board is associated with ASTM C1178 and can go directly over wood or metal studs or over wood subfloors. That gives it a role in both framed-wall and floor assemblies.

Glass-mat water-resistant gypsum backer board is associated with ASTM C1658. Fiber-reinforced water-resistant gypsum backer board is a separate category associated with ASTM C1278. These are material distinctions, not interchangeable grades of cement board.

CBU means cementitious backer unit, the trade abbreviation you’ll encounter when discussing cement-based tile backing.

James Hardie HardieBacker: 1/4 inch or 1/2 inch?

James Hardie HardieBacker is a fiber cement tile underlayment for walls, floors and countertops. Fiber cement combines cement with reinforcing fibers. HardieBacker retains its strength and shape after water exposure, which is a good reason to put it beneath tile in bathrooms, laundry rooms and mudrooms.

For a tile floor, buy 1/4-inch HardieBacker unless you need the thickness identified as 1/2 inch to make a transition. That’s James Hardie’s floor recommendation, and it keeps you from adding height without a reason. Account for the board, mortar and tile together at doorways; forcing tile into a tight fit under trim invites broken tile.

HardieBacker panel size	Thickness	Floor-buying verdict
3 feet by 5 feet	1/4 inch	Buy this for floors that do not need the thicker board for a transition.
3 feet by 5 feet	1/2 inch	Buy this when the floor transition needs the thicker board.

For tile wall backer board, 1/2-inch cement board is a common starting point. Match wall thickness to the framing and tile assembly rather than carrying the 1/4-inch floor recommendation onto a shower wall. Hardie Backer Board 500 resists moisture damage, making that resistance a useful reason to choose it for an interior wet-area wall.

Searching for “Hardie backer board siding”? HardieBacker is the fiber cement underlayment beneath tile. For this purchase, choose it for the kitchen floor, bathroom wall or countertop you’re tiling.

HardieBacker is not designed for use over concrete. Keep it on the wood-subfloor and wall jobs it serves. It also provides a noncombustible foundation for tiled fireplace surrounds and hearths, another useful application during Montana’s winter interior-work season.

How to install backer board on a floor or shower wall

For a floor, start with a subfloor that meets the tile-support requirements. Bed the cement backer board in thinset mortar and fasten it with the appropriate board screws or roofing nails. Screws do not replace the mortar bed, and construction adhesive does not replace thinset.

Lay out cement board so four corners do not meet at one intersection, and keep its seams away from the subfloor seams. Most cement boards require alkali-resistant fiberglass mesh tape embedded in thinset over the joints. Buy that tape with the board. Drywall tape and drywall compound belong to a different job.

For a shower wall, settle the board thickness, fastening and compatible waterproofing as one assembly before tiling. Fill and treat the board joints, complete the waterproofing details, and allow mortar to cure for its required period. HardieBacker installation must comply with local building codes.

The Pick

Buy Durock cement board with EdgeGuard for a tiled shower or tub surround, with compatible waterproofing and Durock Tile Backer Screws. Its water durability is the reason to choose it.

Buy 1/4-inch James Hardie HardieBacker for tile over a sound wood-framed floor. Choose the 1/2-inch panel when you need the extra height at a transition. For a tiled fireplace surround or hearth, HardieBacker’s noncombustible foundation makes it the pick.

Frequently Asked Questions

Is cement backer board waterproof?

Water durability doesn’t make a complete shower waterproof. Durock resists water damage, but tile and grout aren’t waterproof, so plan compatible waterproofing along with the board. Treat moisture protection as part of the whole assembly, not something the tile finish takes care of.

How do you install backer board?

For a tile floor over wood, start with a structurally sound subfloor, then bed the cement backer board in thinset and attach it with the manufacturer’s recommended fasteners. Offset the board seams from the subfloor seams and keep four board corners from meeting. Most cement board manufacturers call for alkali-resistant fiberglass mesh tape embedded in thinset at the joints. Liquid Nails isn’t a substitute for thinset, and drywall compound isn’t a substitute for the joint treatment.

What is backer board used for?

Tile backer board provides a bonding surface beneath tile on walls, floors and countertops. Choose the material for the application: cement, fiber cement, specialized gypsum and foam boards have different moisture-protection and installation requirements. On a floor, the structure underneath must already support the tile because cement board doesn’t stiffen it.

How thick should cement backer board be?

Both 1/4-inch and 1/2-inch cement backer board can be used on floors. For HardieBacker, the floor recommendation is 1/4 inch unless you need the thickness identified as 1/2 inch for a transition. Count the mortar and tile in your finished floor height before choosing; thicker board doesn’t fix a flexible floor.

What screws should you use for backer board?

Use cement board screws designed for the board you’re installing and recommended by its manufacturer. Most cement board manufacturers also permit galvanized roofing nails, so screws aren’t the only fastening option. Match the attachment to the panel instead of treating every backer board as the same material.

Can cement backer board be used outside?

Durock has exterior finish-system applications, but that isn’t blanket approval for every outdoor tile or veneer job. For exterior adhered veneer, use an assembly the board manufacturer recommends and covers under its warranty, and follow its installation instructions. Suitability for an indoor shower doesn’t establish suitability for an exterior wall.