Tile Floor Underlayment Options 101

Tile Floor Being Installed over Concrete
© whitestorm / Fotolia

When doing any renovation or home improvement, the two biggest concerns are time and money. Laying a new tile floor is no exception. The easiest way to save both time and money in this instance would be to simply install the tile over your existing floor. But is this practical or even possible in every instance? The answer to that depends largely upon the type of flooring you already have.

Other Sub-Floor Materials Compatible with Tile

Many types of sub-floor work well with tile and can eliminate extra steps. This is especially true if the material does not have an existing covering.

Cement: Many modern buildings use cement flooring, often finished to resemble marble. As long as the cement is level and has texture, it makes for an excellent sub-floor.

Cement Board: This material is not only compatible with tile, it is often used when adding tile over an existing floor covering.

Exterior Grade Plywood: Unlike interior plywood, the exterior grade is treated to prevent swelling when wet. You can install tile over this material using a layer of cement board or a second layer of plywood screwed securely down to the joists.

Sub-floors You Should Never Tile Over

Some sub-floors are incompatible with tile flooring and must be replaced. The following are the most common examples and why they cannot be used with tile:

Drywall: While you can place tile over drywall walls, the paper covering on drywall sub-floors can become torn, which can destabilize the floor coverings.

Non-Sheet Vinyl Flooring: Vinyl tile, multi-layer, or resilient vinyl can create several problems, including moisture intrusion and shifting.

OSB or Interior Grade Plywood: These materials are prone to swelling when exposed to water, which in turn can cause the grout and tiles to crack.

Particle Board: While this type of sub-floor works with lighter coverings, the combination of tile, grout, and thin-set adds too much weight for particle board to handle.

Can You Tile Over Vinyl?

Vinyl floors are very common in bathroom and kitchen settings. Laying tile over most vinyl is risky or impossible due to the risk of shifting. One-layer sheet vinyl is compatible, although it still requires some degree of preparation to install

Tiling Directly

You will need to check and make sure that your sub-floor and underlayment equal at least one and one quarter inches in thickness, as a thinner floor might not be able to hold the weight of a tile floor reliably. Once you are sure that you have a sturdy base to build upon, the vinyl must be lightly sanded to produce a rougher texture.

For some projects, a hand sander will do, although you may wish to rent a disk sander for larger floors. Completely wet-clean the tile before applying, and install using a thin-set tile mortar.

Tiling with Cement Board

The easiest method to install tile over vinyl is to use cement board. Clean the vinyl surface, and screw your cement board down, making sure the screws are long enough to reach the floor joists. The vinyl will serve the same role as a vapor barrier, while the cement board provides an easy surface for affixing the tile.

You may then tile over the board as you would any bare surface. While quick and easy, be warned that this method will add to the overall height of your floor.

Advantages to Removing Vinyl First

There are several downsides to installing over vinyl. For example, removal gives you a chance to examine the sub-floor for signs of damage or rot. If the floor isn’t sheet vinyl, your tile surface may run the risk of shifting. Cushioned vinyl surfaces crate an even greater risk of shifting and are unsuitable for tiling over.

Finally, a vinyl floor which is not evenly attached to the sub-floor will provide less stability to your new tile floor.

Can You Tile Over Tile?

While it might sound strange when asked aloud, the ability to place a new layer of tile over the old is a common question. The answer depends largely upon whether the existing tile is supported by a solid concrete sub-floor and the condition of the tiles themselves. Cracked or broken tiles may be a sign of further damage to the sub-floor or moisture problems.

Additionally, a hollow sound when tapping the tiles is evidence of missing glue, which may cause problems down the road.

Preparing the Existing Tile

Begin by making sure all of the tiles are securely bonded by tapping lightly with a wooden mallet. Remove any loose tiles and use thin-set to re-adhere them. Once all tiles are secure, use a four-foot level to examine the floor for any raised areas. Level these spots using a grinder with a masonry wheel.

Sand the floor using 80-grit to scratch up the surface glaze for better adhesion. You will also want to remove any grout that has become loose or moldy. Vacuum, and then wash the floor with detergent and water to remove any residues. Finally, rinse and allow the floor to completely dry.

Laying the New Tile

You will want to use a latex-modified thin-set for the new tile. Mix in small batches and always comb the thin-set in a single direction for the best grip. Lay each tile, sliding them perpendicular to the combed thin-set. Careful, accurate installation is paramount to getting the new tile layer to stick securely to the older layer.

Can You Tile Over Linoleum?

While generally ill-advised, it is possible to install tile over a linoleum floor if done with care. It makes laying tile much easier if the linoleum was placed using a bonding agent which grows stronger over time. Before attempting to perform this task, you should test the floor for potential problems.

Potential Issues

Make sure the sub-floor is a sturdy material and not a more fragile substance such as particle board, which may break under the added weight. Another major issue is the risk of asbestos, which may be present in linoleum floors installed prior to 1990.

The floor itself needs to be level, or the tiles will not lie properly. The linseed oil present in linoleum can cause the tile adhesive to break down over time, posing further issues. Lastly, be warned that cushioned linoleum or a flexible floor will damage the tile and grouting and should never be tiled over.

Preparing the Surface on a Wood Sub-floor

Linoleum is very similar to vinyl, and thus preparation is very similar as well over a wooden sub-floor. You will need to clean the floor thoroughly to reduce the risk of chemicals seeping into the thin-set.

Pre-fit cement board in a staggered pattern with a space of one-eighth inch between boards and one-quarter inch from the wall.

Lift each piece and apply modified thin-set using a notched trowel as an adhesive. Anchor the boards further using corrosion-resistant screws. Spread thin-set into each joint and smooth it out. Cover the joints with fiberglass tape and add one more layer of thin-set to seal, feathering it smooth.

Posted on Categories Flooring