Yes, you need thinset mortar between your wood subfloor and cement board. Major manufacturers (such as HardieBacker and Durock) require it. It eliminates hollow voids, prevents the board from flexing, and bonds the two layers into a single, solid structure.
Common Mistakes: How to Install Cement Board the Wrong Way
Cement board can be installed directly on a wood subfloor, but it's crucial to follow proper installation guidelines to ensure a stable and durable surface for tile or other finishes. "Yes, you do [use thinset under cement board].
To secure the boards in place they will need to be screwed down. The screws will need to go all the way through your cement board, all the way through your floorboard, and catch onto your joists. We use 50mm screws to do this.
Use thin-set mortar when installing cement backer board.
While plywood and gypsum board remain accessible and affordable options for certain projects, fiber cement board emerges as the clear winner in a head-to-head comparison on durability, safety, and long-term value.
MAPEI recommends the use of MAPEI Large-Format Floor & Wall Tile Mortar or MAPEI Large Tile & Stone Mortar as thin-set under the cement board. If leveling is needed on interior cement board floors, MAPEI recommends the use of a pourable leveler such as MAPEI Self-Leveler Plus over the cement board.
Fiber cement siding is one of the most durable, low-maintenance, and long-lasting siding materials available. With a lifespan of 50 to 100 years, it outperforms other siding options in terms of longevity, resistance to damage, and overall value.
Typically you would use 2” Alkali resistant mesh tape and mortar mix. Best to follow the cement board manufacture's recommendations. I use mortar with mesh tape or kerdi membrane,also with mortar👍 Use that caulking for your corners,grout cracks in them area's.
If you lay tile on top of plywood, it'll expand over time, causing the tiles and grout lines to possibly crack and damage. The tile can't properly stick to wood as it can with concrete. Instead, lay a cement board on top of the plywood first or use a decoupling membrane.
Cement backer board is much heavier than other materials such as drywall or plywood. This makes it more difficult to transport and install, especially for walls and ceilings. Because cement backer board is heavier, more support may be required during installation, increasing the overall labor and time.
Cement Board Thickness for Floors:
Commonly, ½ and ¼ inches of cement boards are suitable for floors. For the installation of boards on the floors, manufacturers use 5/8 inches plywood subfloor. However, if the tile size is more than 12 inches, then there is a need for ¾ inches of subfloor cement board.
To best attach cement boards to your project fixtures, you should use screws designed specifically for concrete board installation. When you buy cement board, the manufacturer may provide these screws with your purchase. If not, look for screws that are finished with a special coating that resists corrosion.
No vapor barrier should go behind your backer/cement board but you should opt for some type of additional barrier between the tile and cement board such as redguard. Reason for this is that if you had, by chance, some moisture get between the backer board and vapor barrier it would be trapped and cause mold issues.
The smooth side is ideal for mastic applications, as it increases adhesive coverage. The textured side is ideal for mortar applications, as it enhances bonding and reduces tile slip. That said, mastic or thin-set mortar can be used on either side of the board without compromising performance.
Although termites do eat wood, they cannot get to the wood in Hardie Board siding because of the fiber cement materials throughout the product. The presence of cement mixed throughout Hardie Board wood makes it difficult for pests to chew through and access the wood that holds the nutrients they need for survival.
Installing Hardie Board siding on a 2,000 sq. ft. home usually costs between $14,000 and $30,000, depending on the product line you choose, your home's design, and local labor rates. Most homeowners can expect to pay $7 to $15 per square foot for a full installation, which includes both materials and labor.
DUROCK Steel Screws, 32 mm (1-1/4) long, are used for applying 12.7 mm (1/2) DUROCK Cement Board to walls or ceilings.
Type N mortar is well-suited for general walls, chimneys, and outdoor facades that face mild weather. Type S mortar has higher strength, which makes it ideal for foundations, retaining walls, driveways, and areas under heavy load. Choosing the right mortar depends on the balance between durability and flexibility.
Cement backer boards (CBU) are not waterproof or water resistant. You will need to use an ANSI A118. 10 waterproofing membrane on top.
Particle Board (Chipboard)
Particleboard is widely used to make furniture, as well as the construction industry as a cheaper alternative to plywood. It's commonly used for shelves, cabinets, and tabletops, as well as subfloors and wall panels.
If cement board, yes, you need thinset mortar underneath. And yes, it must be screwed down. The purpose of the mortar is to provide support.