Durock Subflooring

Durock is an inexpensive subflooring for ceramic tiles. It is made from cement; more specifically, aggregated portland cement board reinforced with polymer coated fiberglass mesh. It is thin but durable sub flooring that is used when the finished floor is going to be ceramic or some other kind of tile, and used frequently in bathrooms especially because it is durable and waterproof.

Since Durock underlayment paneling is not meant to be a structural load-bearing member, it needs to be installed on a sub-flooring itself, and not just attached to floor joists. It does, however, create a solid surface to attach ceramic tiles to.

This is NOT a one-day installation so you will have to plan for that and have an alternate bathroom for about four days to make sure everything dries properly and stays tight. You might want to consider having a helper or two at least for taking up the old flooring. Durock installation kits are available at your building materials store, that come with screws and adhesive. Remember to work with adequate ventilation when you are using the adhesives.

Durock is available in a few different types. The one you want for subflooring is the 5/16 inch thick panels.

Preparing for the Durock Subflooring

You will need a few tools to start with. A tape measure, hammer, nails and screws, screwdriver, a drill, drill bits , and a circular saw with carbide-tipped blade if you have one.

You might also need a shovel and a crowbar should you have to remove old flooring before starting the new project. If you are doing a bathroom you will also need new hold downs for the toilet and a new wax ring when you re-seat it on the floor after tiling the floor.

Before putting in a new tile floor, you need to pull up what ever floor covering is in the room now. You can’t leave it there and go over it because you will wind up with a mess when the new floor cracks in a year or so.

In a bathroom you will want to check the floor itself and beams for water damage to make sure you haven’t had a leak that rotted the wood. If this is the case you will have to replace the existing sub floor that is soft before going any further with your project. Use Oriented Strand Board or exterior grade plywood of at least 5/8 inch thickness.

Installing Durock Panels

If the original plywood subfloor is to remain, make sure it is nailed or screwed down tightly. After measuring your surface area, mark off the required size on the durock with a pencil. Score both sides and edges of the board with a utility knife, cutting through the fiberglass mesh cover, and snap the board apart manually. You can also use a power circular saw with a carbide blade.
The next step is to apply your adhesive.

Using a notched trowel, spread thinset mortar on the existing subfloor. What this does is "Laminates" the board to the floor. By doing this, you compensate for imperfections in the subfloor, leveling it and filling voids that just screwing it down cannot.

Lay the durock panel smooth side up and fasten it to the wood floor about every 8 inches. You’ll be using either1 ¼ inch wood screws or 1 ½ inch galvanized roofing nails. Make sure the screws are slightly below the top of the durock so that when you put the leveling agent on top of the durock it will fill in the screw heads and keep them from coming through your new floor.

Leveling and Tiling

After a leveling agent has been applied, it needs to dry before you can continue and lay the tiles down. Once it has dried you can get your tile adhesive and put the tile floor down. If this is in a bathroom, when you grout the tiles, don’t use grout by the tub or toilet edges (you won’t do the toilet until the very last thing in the room). Get a colored acrylic caulk instead. The grout is stiff and will crack, the caulking is flexible.

Once the floor is dry and the grout is cleaned up, it is time to re-seat the toilet on the wax ring. When you take the wax ring out of the package make sure it is room temperature before trying to use it. It is made to form to the pipe on the toilet and make an air and waterproof seal between the pipe and the toilet.

Once the toilet is seated, drill new holes for the new hold downs. When drilling the holes you will want to go all the way through the durock and wood under it so you have a stable base to tighten the bolts to. Once this is finished, you can install a great looking tile floor that should last a long time.

Durock Material Safety Data Sheet: pdf