Certain projects need a substrate that’s more durable or more water-resistant than standard drywall or wood. For those jobs, cement backerboard is typically the material of choice. This reliable material can withstand some tough conditions, lasting for years when installed correctly. This guide will break down only what cement backerboard is but also when to use it and how to install it.
Cement backerboard has its advantages and disadvantages. On the one hand, it can serve some of the same purposes as drywall or plywood, but with additional durability. On the other, it’s heavy, comes in smaller sheets, and can be a bit of a pain to work with. But, despite its challenges, there are plenty of projects—from installing flooring to setting tiles—that require cement backerboard, so DIYers should get to know this material.
Read on to learn what cement backerboard is, when to use it, and how to install cement backerboard properly.
Cement backerboard is a sheet good designed to provide a stable base for tile or masonry projects. The material itself consists of a thin layer of concrete sandwiched between two layers of fiberglass.
This material has several names, many of which are brand names. It’s often called Durock, Hardie Board, HardieBacker, or simply cement board. It usually comes in ½-inch or ¼-inch thicknesses and in sheets measuring 3 feet wide by 5 feet long to keep the panel as light and manageable as possible (four-foot by eight-foot sheets do exist, as well). The ½-inch variant would be most suitable for flooring, while ¼-inch is ideal for walls, and most sheets range between around $15 and $18 each.
Because the material is very tough and unaffected by water, cement backerboard is compatible with a variety of surfaces. It can be laid on top of drywall before tiling walls or ceilings, or it can be attached directly to the studs and joists. It can also be installed on top of a subfloor, though it cannot be installed directly on floor joists. and.
Cement board has several purposes. It’s most commonly used as a substrate when installing tile installation. The concrete surface is much more stable and level and provides a stronger bond to the tile than plywood, which makes it an excellent surface for tile floors. Because it can support the extra weight and can withstand the elements, it can also be used outdoors as a substrate for veneers and stone installations. But it’s also popularly used in moisture-prone rooms, like bathrooms and laundry rooms.
Cement backerboard isn’t necessarily waterproof, but it is unaffected by water. This means that it doesn’t deteriorate if it gets wet, but it won’t block water completely (though most are labeled as “water-resistant”). So it makes a great choice for bathroom walls, ceilings, and floors during tile installations. These installs do require a vapor barrier behind the cement backerboard, however, as the material itself is not waterproof. Though cement backerboard itself is mold-, rot-, and warp-resistant, the framing behind it is not.
Reach for cement backerboard when:
- Installing floor tiles on a plywood subfloor
- Installing tiles in moisture-prone areas like bathroom walls, floors, and ceilings, as well as shower surrounds
- When designing countertops made from individual tiles.
- When adding a brick or stone veneer, a masonry skim coat, or stucco to an exterior object like a faux-stone wall, a mailbox column, and similar structures
There are cases when using a cement backerboard is not necessary. It’s heavier than drywall, more difficult to cut and shape, and the texture is rough, meaning that it’s best to avoid using cement backerboard on projects that don’t require it (or aren’t suitable).
For instance, when tiling a wall in a room that is unlikely to experience splashing or a ton of moisture such as a mudroom or another similar space, cement backerboard isn’t necessary. Also, if the wall won’t be tiled or skim-coated with a plaster or stucco, you would not want to use cement board as its texture is too rough to smooth with a joint compound skim-coat.
The following steps will explain how to install cement backerboard over a subfloor for a floor tile installation. The steps are largely the same for walls, however applying thinset is typically not necessary.
You Will Need:
- ½-inch cement backerboard
- Measuring tape
- Heavy-duty carpenter’s pencil or permanent marker
- Utility knife
- ¼-inch notched trowel
- Cement board screws
- Thinset (premixed is easiest)
- Mesh drywall tape
- Putty knife
1. Remove any existing flooring until the plywood or tongue-and-groove subfloor is exposed. If the floor requires repairs or any sections of the subfloor need to be screwed back down, do so now.
2. Dry-fit a few sheets of backerboard at a time. When you lay them in place, position them so the backerboard seams don’t line up with the existing plywood subfloor seams and make sure to also stagger joints for each row. Leave a ⅛-inch gap between the sheets and a ¼- to ⅜-inch gap between the edges of the sheets and the wall.
3. Before making any cuts, measure and mark the concrete backerboard. Use a utility knife to cut the fiberglass mesh at the mark, and then cut through the rest with a jigsaw at the marked line. Test-fit the piece to ensure it fits well and remove the sheet of cement backerboard.
4. Working one sheet at a time, apply thinset to the floor. Spread it out with the flat side of the trowel and then create ridges with the notched side.
5. Lay the cement backerboard down onto the wet thinset. Wiggle it back and forth until it’s fitting properly in the space, maintaining a ¼-inch gap between the edge of the sheet and the walls.
6. Fasten the cement backerboard in place by driving cement board screws through the cement backerboard and into the subfloor below. Starting about an inch in from the edges, drive a screw every 8 inches. Be sure to continue driving the screw until the head of the screw is slightly below the surface of the cement backerboard, similar to how you would install drywall. Move on to the next piece of cement backerboard.
7. Once the entire floor has been covered in cement backerboard and fastened into place, it’s time to tape the seams between the boards Note: Do not tape the seam between the edges of the cement backerboard and the wall.
Starting one seam at a time, use the putty knife to apply a 3- to 4-inch-wide bead of thinset across the joint. Apply the tape over the thinset and push it in with the putty knife before smoothing out any lumps, high spots, or gaps. Tape the rest of the seams in the same fashion.
8. Allow the thinset to dry for a few days before you begin tiling. The thinset underneath the cement board won’t breathe well, so it will take some time to dry.
With a solid understanding of cement backerboard, you’ll be able to start your tiling or masonry projects off on the right foot every time. Just be sure to stagger joints, use plenty of screws, and give the thinset time to dry, and that subfloor will never move, ensuring tiles stay put for a long-lasting floor.