How to Prepare Your Subfloor for Tiles

There are many advantages to installing tile floors. Tiles are much easier to maintain and clean than carpets due to their protective surfacing. They’re resistant to humidity, making them perfect for humid rooms such as kitchens and bathrooms. And, they’re good looking as well.

If you’ve been thinking about replacing your existing flooring with tiles, there are a couple of things you need to keep in mind. High-quality ceramic and porcelain tiles look good, but they’re incredibly rigid and can crack if there’s any movement in the floor surface. That’s why having an adequately prepared subfloor is so essential. It ensures that the subfloor is stable and won’t move under the tiles. It also provides a surface that grout can adhere to, giving the tile layer additional stability.

The type of subfloor you have will determine your preparation steps. However, as Home Depot illustrates in their video guide, the basic principles remain the same for all subfloor types. So if you want to start laying some new tiles, be sure to get your subfloor sorted out first.


What You Need

  • A spirit level
  • Caulk and a caulking gun
  • Liquid primer sealer
  • Liquid self-leveling underlayment
  • Concrete backer board for wooden floors
  • Thinset, or mortar for the laying of the concrete backer board
  • Electric drill
  • Cleaning tools

Step-By-Step Breakdown

Wooden Subfloors

1. Check that the floor is even.

The first step in getting your wooden floor ready is to check if the floor has any dips or unevenness by sliding a long spirit level over the floor. You’ll quickly notice any dips where the level doesn’t touch the floor. Mark those in preparation for filling.

2. Use underlayment to even the floor.

While the idea of laying down underlayment may seem tricky if you’ve never done it before, it is quite simple. You start by mixing up the appropriate underlayment for your floor in a bucket.

If you have a wood floor, first ensure that it’s watertight by applying caulk to any seams in the subfloor. This step is followed by the application of a layer of liquid primer sealer, which seals the wooden surface, preventing it from absorbing moisture from the underlayment. It also improves the bond between the self-leveling underlayment and the floor, guaranteeing even coverage.

3. Pour the self-leveling underlayment.

As the name suggests, a self-leveling underlayment will flow down into the lowest area and even out. Make sure to never pour this underlayment onto a porous surface which will swell and become uneven. Stick to wood or concrete subfloors as they’re the best materials to hold the tile.

The liquid underlayment will create a flat and even surface when dried, and then you’ll be ready to move onto the next step.

4. Attach cement backer board to the floor.

Having a cement backer board provides your subfloor with additional stability and structure. The first step in this process is to mix up some polymer-modified thinset that will attach the backer board to the wooden floor. Make sure to wear the correct safety equipment when mixing this material, as it’s powdery and may get into your eyes and lungs. Follow the directions on the packaging to mix this up, and use a drill to mix the thinset thoroughly.

Also, make sure not to mix up a large batch of thinset at once. As it’s a mortar, it starts to dry very quickly and has a limited use time. If you mix up too large a batch, you may find yourself throwing half of it out. You do want to take your time while laying the thinset, so mix up small quantities as you work your way through the entire floor.

Once you’ve mixed up your thinset, apply it using a trowel, starting in one corner of the room. Aim to cover an area that’s slightly larger than your first piece of concrete backer board. Make sure that you’re using the comb of the trowel at a 45° angle and that all the lines are going in the same direction.

Once you’ve got your mortar ready, place the first sheet of the concrete backer board onto the thinset.

Secure the backer board to the floor by walking gently over the board, as well as using special screws to screw the backer board into the plywood floor. Drive the screws every 8″ of the backer board. If you’ve bought a fancy backer board, you’ll see that the manufacturer has marked the locations of the screws for you.

You’ll continue this process for the entire floor, laying thinset and securing backer board over the entirety of your floor. When laying the backer board, make sure to leave a quarter inch gap from the wall, and use a nail to create a gap between the various backer board pieces.

Stagger the sheets so that the edges are not aligned with each other. Try also to avoid having the edges of the backer board align with the seams of the subfloor, as this creates areas of instability and weakness.

After you’ve placed all the backer board sheets, you can remove the nails that you had previously used as spacers.

You can reinforce these joints with some specially made backer board tape, also known as self-adhesive, alkali-resistant glass fiber tape.

Cover the tape with thinset and level it with a straight-edge ruler. Give the thinset a day to dry, though this may depend on the manufacturer. After this final step, your wood subfloor is ready to be tiled.

Concrete Subfloors

1. Test for water penetration.

If you have a concrete subfloor, you’ll find the process is much more straightforward than for wooden subfloors. Firstly, spray your concrete subfloor with water in various places. If the water remains as a continuous wet spot, you can continue preparing your subfloor. If the water beads, you first need to clean your surface of any contaminants that can interfere with the bonding process.

2. Ensure your concrete is rough.

Ideally, your concrete subfloor should have a coarse finish to form a strong tiling bond. If your concrete subfloor has a smooth finish, you’ll need to use agents such as muriatic acid to etch it.

3. Check and repair dips in the floor as discussed for wood floors.

Since you want your concrete floor to be completely level, use a spirit level to check for dips. If you identify any dips, use self-leveling underlayment to even out the dips.

4. Ensure your floor is clean.

Before you start laying tiles, you must ensure that your floor is clean of any dirt, debris, oil, or chemicals that can negatively affect the bond between the subfloor and the tiles. Once the floor is clean, you may start the process of laying your tiles.


Preparing a subfloor is an essential step of the tiling process. It ensures that the tiles remain stable and will not crack due to floor movement or changes in floor pressure. Concrete subfloors are relatively simple to prepare for tiling, while wooden subfloors need a bit more care and effort. In the end, you need to have a level, stable foundation that your tiles can rest on.

There are many other products you can use to enhance further the stability of your subfloor, such as crack prevention membranes and waterproofing membranes, which you can apply after the subfloor has been cleaned and before the mortar has been laid for the tiles.

If you’re saving money by installing your own tile have you ever wondered how to saw porcelain tile using a reciprocating saw or a chop saw or any other similar type of tool? Though it’s not ideal it is very possible.

No matter what type of subfloor you have, by taking the time to prepare it correctly, you can significantly expand the lifespan of your new tile floor.

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