Why Underlayment Matters to a Tile Installation Project

Tile-installation-underlayment (350x277)

Are you planning a tile installation project? If yes, don't forget underlayment!

Underlayment in a tile project can mean the difference between a project that lasts for years and one you have to redo because an unexpected crack develops in your concrete slab. As Jason Schmitz, former assistant store manager for Tile Outlets in Fort Myers and tile installation expert, says "underlayment is like an insurance policy."

We caught up with Jason to find out more about underlayment and why it matters so much when you're installing tile.

Jason Schmitz Explains Why Underlayment Matters to a Tile Installation Project

TOA: Jason, what is an underlayment and why use it?

Jason: Underlayment is any product that can be installed under a flooring system to solve a problem. For example, to provide more rigidity for a tile installation, to prevent subfloor cracks from transferring to the tile installation, to provide sound proofing, as well as to protect from moisture from coming through the subfloor and affecting the finished floor.

You'll find that different types of underlayments accomplish different purposes.

Now, there are self-leveling underlayments that are Portland-based cement products that are mixed into a thin consistency and poured onto an area until it finds its own level. You would then add underlayment and install tile.  I'm focusing on underlayments applied on top of the prepared and level subfloor.

TOA: When would you not use an underlayment in a tile project?

Jason: There are times when you might not use an underlayment. For example, if you have carefully prepared the subfloor; it is completely clean and level and you can confirm that you have no moisture issues to deal with.

In South Florida, most homes are built on concrete slabs that you can technically install tile over. However, these slabs can crack over time and when and where is anyone’s guess - especially on new floors. A crack in the slab can transfer to the tile you've just installed. An underlayment membrane helps prevent the transfer of cracks.

The decision not to use an underlayment can be a cost issue.  A crack membrane - the most expensive kind of underlayment - can add ~$1/square foot to the average installation. However, when you do have a crack situation, you discover that it's a lot more expensive to have to redo the installation.

That's why I consider underlayment just like an insurance policy for a tile installation project.

TOA: How do you choose underlayment for a tile installation project?

Jason: You need to know which problem you want to take care of since there are many different types of underlayment available and they're available in different forms.

  • Sheet – a 3x5 cement board such as Durock or Fiberock which is applied on the wood subfloor to help with deflection (i.e., movement up/down). This makes the floor more rigid and suitable for tile installation.
  • Liquid applied membrane – it is applied with a roller or trowel for crack prevention. It requires at least 4-6 hours drying time before you can walk on it and a minimum of 8-12 hours before you can install tile. It's less expensive (~$60 in liquid to cover 150 sq. feet) than a peel/stick membrane and fairly simple to install. Just follow the instructions.
  • Peel and stick membrane – also addresses crack prevention. You can immediately apply tile right on top of it. It includes a lifetime warranty against cracks if applied correctly. The watchout with peel and stick membrane is that you must use a primer (preferably, the manufacturer's primer). This product with the application of primer costs approximately twice as much as the liquid applied membrane.

You can apply peel and stick membranes for sound absorption on a 2nd floor wood floor. The sound absorption membrane is very similar to crack prevention membrane, only thicker. It is meant to deaden sound that goes below a floor. On the ground level, there's really no sound to worry about.

Peel/stick membranes offer other benefits: you can safely cover asbestos flooring (for example, vinyl tile in older homes) and encapsulate it. You can use it as an effective barrier against radon as well as to prevent moisture vapor transmission through a concrete slab and into the home.

TOA: What are the differences between Fiberock and Durock?

Jason: Both are cement board products that you can use on walls and on floors where they help address deflection (i.e., up and down movement) in a subfloor.

  • Fiberock is fiber based and not 100% cementitious (i.e., not completely made out of concrete). Fiber reinforces the concrete. This product is only suitable for indoor use. In a shower installation, you want to make sure that it is off the shower pan so the fiber doesn't rot with exposure to water.
  • Durock is a true concrete board and can be used outdoors as well as indoors. It is now available as Durock NextGen which weighs about 1/3 less than the standard concrete board. This product cuts easily - simply score and snap it, just like drywall.

TOA: How big a problem is moisture for tile in Florida?

floor-tile-tenting-John-Bridge Floor tile tenting - image from JohnBridge.com

Jason: Moisture can be a big problem for tile. In Florida, we have dry winters and wet summers. Most of our homes are built on concrete slabs.

When it's dry, the concrete slab contracts; when it's wet, it expands. As the slab contracts, it pushes together and forces tiles installed on it to buckle in the middle; that's called tenting. During winter, you'll hear a big noise if tenting happens. Essentially, the weakest link in the installation goes. It can be the grout or the tile itself can pop loose if it’s the weakest link of the installation. If that happens, you have to redo the entire floor because the the movement of the slab is such that the tiles will not longer fit.

An underlayment membrane allows the slab to move without affecting the surface. (See Floor Tile Installation Problems – “Tenting” on JohnBridge.com.)

TOA: What are the biggest issues faced when using underlayment?

Jason: You want to make sure to use the right product for the right application.

For example, a crack membrane - meant for lateral or horizontal cracks in a concrete subfloor - will not protect a tile installation from cracks generated from the up/down movement generated by a flexing wood subfloor.

Next, you want to properly install the underlayment. In other words, completely and thoroughly follow the manufacturer's instructions so you know if the underlayment needs to be thinset down and a screw added every 8 inches. Read the instructions! You'd be surprised how many people don't pay attention to installation instructions.

TOA: Jason, which products can customers find at Tile Outlets of America stores?

Jason: We carry a full selection of underlayments in all Tile Outlets stores. You'll find Durock, Fiberock concrete underlayment as well as NAC Building Products crack and sound membranes and Parex USA liquid applied membranes (e.g., HydroGuard). You can visit Installing Tile: What Underlayments You Need on the Tile Outlets website for a listing of the underlayment and waterproofing products that we carry.

And don't hesitate to ask questions about underlayment and how it helps a tile installation project when you visit the stores.

TOA: Thank you, Jason.

Have you recently installed tile and used an underlayment? What was your experience? Have you had a situation where you wished you had used it? Let us know in the comments.

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