The Best Tile Underlayment Options Depending On Your Subfloor

Kenneth Wilson

If you’re about to lay a new tile floor at home, selecting your preferred tiles is only one part of the process. Equally as important is your consideration of the subfloor upon which the tiles will be laid, as well as the level of underlayment that sits between.

But what different types of underlayment can you use? And how do you select the perfect type of tile underlayment for your subfloor?

We answer these questions and more in this article as we present an informative guide on how to pick the right tile underlayment for your home flooring project.

What is the Purpose of Tile Underlayment?

Tile underlayment is the middle layer of your tile floor and sits between the subfloor and the surface tiles that you walk upon when the floor has been laid. The primary role of tile underlayment is to smooth out any uneven points in your subfloor to enable you to lay your tile floor on a flat surface.

What’s more, underlayment acts as a waterproof barrier between your tile surface and the subfloor beneath, which is ideal if you’re planning to lay a tile floor in the bathroom or kitchen, where moisture levels are high. (Related: Do You Need An Underlayment For Tile On Concrete? (A Comprehensive Guide))

But as we explain below, there isn’t just one type of tile underlayment worthy of your consideration, and the various products can be separated into three broad categories.

The Three Primary Types of Underlayment for Tile Floors

It’s really important to understand the different types of tile underlayment, so you can pick the product that works best for your subfloor and chosen tiles. We introduce each type of tile underlayment below and help you decide which is the best option for your project.

1. Backer Boards

Backer boards have been around for decades and are among the most popular type of tile underlayment. They’re favored by professionals laying ceramic or porcelain tile floors and are typically comprised of cement, fiberglass, and crushed glass particles.

According to the Tile Council of North America, there are several different types of backer boards that you can use, including:

  • Cement backer boards
  • Coated glass mat water-resistant gypsum backer boards
  • Glass mat water-resistant gypsum backer boards
  • Fiber cement backer boards
  • Fiber-reinforced water-resistant gypsum backer boards
  • Cementitious coated extruded foam backer boards

Each type of backer board introduced above can be used as tile underlayment, but an additional layer of thin-set mortar is required to affix the underlayment to the subfloor, which is a process in the industry known as bedding.

Backer boards have long been a popular choice when installing tiles, as they serve as an excellent bridge for your surface tiles and prevent them from cracking once laid.

2. Floor Underlayment Preparation Materials

If your subfloor is relatively flat and blemish-free, you don’t necessarily need to install backer boards before laying your tiles. There are several different preparation materials you can use for underlayment, as we introduce below.

  • Mortar Beds - You can lay a bed of mortar or something similar in order to directly lay tiles on top of a concrete slab. Although mortar beds have been used for years, they are not as popular today as they once were. The main reason that they’re no longer popular with professional tilers is that preparing a perfect mortar bed takes a lot of time and skill. It’s also important to note that mortar beds add significant weight to your structure, as they are composed of relatively thick cement, which rules them out of use in many tightly engineered buildings in the present day.
  • Thin-set Mortar - A viable alternative to traditional mortar beds is a layer of thin-set mortar, which typically comes as a thin powder that needs to be mixed with water. While thin-set mortar is usually applied in conjunction with backer boards, tiles can also be laid directly on top, providing that the subfloor is particularly flat and doesn’t contain cracks. Because thin-set mortar is (obviously) thinner than traditional mortar beds, it won’t be suitable for use with heavier ceramic tiles or when laid upon subfloor surfaces that are cracked or slightly damaged.
  • Floor Patches - If your subfloor is cracked or damaged, then you can install a floor patch to serve as your tile underlayment. Patches fill cracks, voids, and rough surfaces and can be used to cover depressed areas within the subfloor. While they vary in their composition, floor patches are typically made of latex and are mixed with potable water. Ultimately, if you’re looking to repair a damaged floor before laying tiles, then floor patches are your best option.
  • Trowelable Underlayment - Trowelable underlayment usually combines aggregates, cement, and a latex additive, which is applied directly to the subfloor, sometimes atop a pre-laid slurry coat. In many respects, trowelable underlayment is similar to a mortar bed. Once it has been applied and dried, the surface needs to be sanded and evened out to remove any trowel ridges. This process is quite labor-intensive and takes more time than other approaches. And depending on the finish, you might need to lay more than one coating.
  • Self-Leveling Underlayment - If your subfloor is in particularly poor condition as you prepare to lay your tiles, you can opt for self-leveling underlayment or SLU. It’s impossible to understate the importance of leveling your floor before adding your tiles, as it will prevent cracks from appearing in the future and will ensure your floor is even and well laid.

3. Membranes 

The third and final type of tile underlayment you can apply to the subfloor is a membrane. Membranes are made of polyethylene and typically come in rolls, which are designed to protect your floor from moisture and cracks.

There are several different types of membranes that can be added to your subfloor, and the product that you opt for depends on where you are laying your tile floor, as we explain below.

  • Waterproof membranes - One of the most popular types of membranes used for tiles are waterproof membranes, which are available in both sheet and liquid forms. Thanks to their waterproofing properties, these types of membranes are commonly used in showers or wet rooms, as they prevent leaking through cracks that may otherwise exist in the floor.
  • Crack isolation membranes - If you’re installing a delicate type of tile, for instance, thin-bed ceramic or glass tiles, you can install them with the aid of a crack isolation membrane that isolates the tile from minor in-plane substrate cracking. Most crack isolation membranes require professional installation, as they need to be bonded directly to the substrate in order to function properly.
  • Uncoupling membranes - Instead of using a traditional backer board, you can opt to use uncoupling membranes as your tile underlayment. They come with a type of bonding scrim or mesh that is then bonded to your wood or concrete floor. They’re used to absorb movement within the substrate and prevent your tiles from cracking.
  • Bonded Sound Reduction Membranes - If you’re hoping to reduce the sound that your tiled floor makes, then you could opt for a bonded sound reduction membrane as your tile underlayment. These membranes can be trowel applied or affixed as sheets, depending on your requirements and skill level.

Choosing the Right Type of Tile Underlayment for Your Subfloor

As you can see from our extensive list of tile underlayment types, there are multiple options to choose from. And there isn’t universal agreement on which type of underlayment is the best, as every floor is slightly different from the next.

In order to choose the right type of tile underlayment, you first need to consider the condition of your subfloor, as this will often dictate what type of underlayment to proceed with. For instance, if you’re laying tiles on a perfectly flat concrete surface, a layer of thin-set mortar should do the trick.

But if the surface is damaged or cracked, you would be better served opting for a backer board or an uncoupling membrane as your underlayment.

You will find that the tiles that you choose come with a manufacturer’s recommendation, too, so you can use this to guide you as you look to lay your new tiles. But if you’re really struggling to come to a decision about which underlayment to opt for, it’s a good idea to consult a tiler or fitter to advise you and perhaps assist you with the project.

Final Thoughts

Unfortunately, it’s impossible to recommend one type of tile underlayment over another, as your choice will depend upon the condition of your floor and the specifics of your project. That being said, we hope this guide provides you with the information that you need to proceed with your DIY tile project or highlights the need for you to consult a professional!

Kenneth Wilson
December 22, 2021

Kenneth Wilson

Retired contractor. Currently residing in Southwest Florida. Now in semi-retirement, I write and manage this blog focused on helping home owners make savvy decisions when it comes to finding contractors and getting their projects done. I also operate remodeling design service for homeowners.

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