Installer Briefing: Heated Floor Installations Tile and stone industry keeps up with increased demand for warm floors
May 1st, 2004

By Bart Bettiga May-Jun 2004

The ceramic tile and natural stone industry has experienced enormous growth over the last several years. A healthy economy, trends in building larger kitchens and bathrooms and increased consumer demand have contributed to this trend.

In addition to market trends, advancements in technology have helped drive increased tile and stone usage. Improvements in both tile and stone production as well as the products to install them have played a large role in our industry’s explosion.

Perhaps no other advancement in technology has had a bigger impact than the increased use of radiant heating in tile and stone installations. Designers and architects have always loved the look of our products, but for years homeowners objected to them due to the cool surface. Radiant heating has eliminated this objection. Tile and stone now offer an inviting source of warmth. Initially, radiant heat was used primarily in cold weather markets, but that has recently changed. With radiant, tile may be turned on to be warm in cold weather, then turned off for a cool feel in warmer months. Tile is thin, but also dense and conductive, thus it transfers heat exceptionally well.

Hydronic Systems

According to the Radiant Panel Association, hydronic tubing sales nearly doubled in four years. In 1998, 121 million square feet of hydronic tubing were shipped in the United States. By 2002, this number had increased to 213 million square feet, a whopping 44% increase! These systems are usually used when the customer wishes to heat a large area, often the entire house. The decision to use hydronic systems is generally made by the builder and the client, not the distributor or tile contractor. The challenge to the contractor is to install the tile correctly over hydronic tubing.

The Tile Council of America Handbook for ceramic tile installation recognizes three ways to install tile over hydronic tubing systems. The first installation (F111-03)[Editor's note: numbers refer to installations in the Tile Council of America Handbook] over a concrete subfloor outlines a situation where the radiant heating tubes are laid over the slab. The contractor must screed fill flush to the top of the pipes before placing a cleavage membrane and reinforced mortar bed in place. At this point, the contractor can install over a workable mortar bed or come back later and apply the tile with a dry set or latex modified mortar on a cured bed.

Installation F141-03 requires a wood subfloor in which the radiant pipes are installed in the same way as F111-03, over the subfloor with screed fill flush to the top of the pipes. The cleavage membrane and reinforced mortar method is the same process as well. It is important to note the required subfloor is 19/32-inch plywood or 1-inch nominal boards when joists are 16-inches on center.

A new hydronic method in which the pipes are encapsulated into a poured concrete floor was introduced in 2003. This method, (RH110-03) calls for the tubes to be installed into the mortar. The portland cement must be at least ¾-inch over the top of the tubes. It is also important to note that this detail calls for a crack isolation membrane to be applied to the substrate prior to the installation of the tile. Distributors and contractors should consult with the manufacturers of both the crack isolation system and the adhesive manufacturer to be used for specific installation instructions.

It is also important to note that in many markets gypsum-based underlayments are being poured over the hydronic tubing where tile is to be installed. The National Tile Contractors Association considers gypsum-based underlayment to be a questionable substrate, as it expands and contracts at a different rate than cement. This does not mean that you cannot successfully install tile over this system. It does mean that you need to consult with the adhesive manufacturer and the crack isolation manufacturer to ensure you are covering your bases when tiling over this system. Get a written warranty blessing your process! This is your best insurance on a job of this magnitude.

Another popular method being used today involves the use of cementitious, self-leveling underlayments. These systems are installed by the tile contractor, and can be pumped or mixed and poured over the tubes. Generally this is done in two pours.

In this scenario, a primer needs to be applied to the first pour to prevent a cold joint. Again, consult with the self-leveling manufacturer for proper instructions. An advantage to this method is that the manufacturers of mortar systems generally also make the self-leveling products, leaving the contractor with a better chance of achieving a solid warranty.

Electric Systems

The use of electric radiant heat systems has simply exploded in recent years. An electric system may be the best choice for small areas like a single master bathroom. Typically, low-profile electric floor radiant systems are installed right in the thinset used to set a finished tile or stone floor. A thermostat controls the temperature of these systems.

There are many manufacturers of electric radiant heat systems. Some products come in mats; others are cables attached to the substrate or rolled goods with the cables already inside of them. Most of these systems must be embedded in the thinset. The Tile Council of America introduced three new methods for electric radiant heat systems in the 2003 Handbook. Follow these instructions carefully. The three methods outlined provide details over concrete (RH115-03), cementitious and fiber cement underlayments, (RH135-03) and a double layer plywood system (RH130-03). Be sure to consult with the manufacturer of the underlayment being used for their installation requirements. Specifically ask them if a crack isolation system is required.

The National Tile Contractors Association also recommends that the tile contractor apply a bond coat with the flat side of the trowel to the substrate. Then, the electric system is applied to the bond coat prior to the installation of the tile. When installing tile over electric systems, you need to make sure you are not troweling the thinset being used thicker than an adhesive manufacturer will allow. Consult with the manufacturers for specific installation instructions and product recommendations over these products. This includes the adhesive, underlayment and electric system manufacturers.

Many of the electric system manufacturers have outstanding websites which help you to lay out the floor and to price the project quickly. Also pay close attention to requirements in the TCA Handbook for the use of expansion joints provided in detail EJ171. Costs of these systems vary, but when a consumer really looks at the value added to the home, the investment is often justifiable.

It is important to note that crack isolation systems are not required in the TCA Handbook details on electric radiant heat systems. This does not mean they should not be considered.

Methods for installing tile, stone and marble over these systems are evolving. Get specific installation instructions in writing to protect yourself. Also, the TCA Handbook Committee will be meeting in the summer of 2004 for further method updates. Play close attention to the 2005-2006 Handbook release to see if any changes or modifications occur. Contact the Marble Institute of America for their recommendations for natural stone installations over these systems.

Sources For Information

Specific manufacturers’ websites are helpful but a word of caution is necessary because they are proprietary in nature. Other sources to be considered include the Radiant Panel Association at 970-613-0100 or You may also want to consult with the Tile Council of America at or the Marble Institute of America at for specific details regarding tile or stone installations over these products.

Bart Bettiga is the Executive Director of the National Tile Contractors Association and a former President of the Ceramic Tile Distributors Association. The National Tile Contractors Association, established in 1947, represents the entire tile and stone industry and is dedicated to providing quality education to ensure proper installations. For more information, contact NTCA headquarters at 601-939-2071 or

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