#MAPEITechTip: Soaring Summer Temperatures—Installing Tile or Stone in Hot Weather

It’s 10am in South Florida and the temperature is already pushing 85°F with 75% humidity. Meanwhile inside on the project, you’ve been busy prepping the concrete substrate for the 24” x 24” porcelain tiles you will be installing—suddenly you realize you left the mortar and grout out in the pickup.  While the temperature outside is 85°F, the temperatures inside the pickup can easily reach 20°F - 40°F degrees above that temperature.  How can baking the mortar and grout affect your installation?

Taking the bags of mortar (including the liquid-latex additive) and grout directly from a hot pickup and immediately installing them on a project, can run the risk of failure—How?  Unlike site mixes that were the norm a few years ago, packaged mortars and grouts are more highly engineered using ingredients like calcium aluminates (in place of Portland-based Cements) and polymers, making them more susceptible to ‘flashing off’ if not properly acclimated.  Under such conditions, cement mortars and grouts dry out much faster with much less open and working time (typically 20 min.) as well as a faster rate of skinning over.  Most installation product manufacturers have specific product storage, handling and installation procedures, that’s why most industry specifications only recommend setting tile or stone between 50°F and 95°F.  This problem is compounded when installing tile or stone outside, where acclimating the products may mean using a garage, erecting a tent to provide cover during storage and application, and in extreme situations using cool water to mix or keeping the liquid-latex container in a bucket of chilled water. Also adjusting your installation methods by controlling: 1.) liquid-powder mixing ratios  2.) amount of mortar that is troweled and combed before setting the tile can help. Understanding your 'installation environment', such as high temperatures, crosswinds and low relative humidity can combine to produce a skin on a mortar (select a mortar with extended open time and high deformability ISO 13007 C2ES2) in just a few minutes. Cutting down on the size of the area that is spread, and periodically checking to ensure that the bond from the back of tile to the substrate has not been compromised by excessive heat or wind.

When weather or storage conditions don’t comply with those specifications, common sense is the best defense—understanding how heat, humidity, dryness and wind affect setting mortars and grouts and taking appropriate precautions before, during and after tiling will ensure a successful installation in these conditions. The most current NTCA (National Tile Contractors Association) Reference Manual on “Hot Weather Tiling” defines it as “any combination of high air temperature, low relative humidity and wind velocity that affects the performance of setting and grouting materials.”  Often in hot weather, the natural tendency for most installers is to use higher proportions of mixing water or latex in the mortar preparation. This “solution” invariably results in excessive drying shrinkage, improper curing and poor physical strength. In addition, the installation becomes less durable when recommended mixing proportions are not followed.

Exterior installations in subtropical climatic conditions endure great stress from the thermal variations between the cool of nighttime and the direct sun exposure of daytime. Sudden rainstorms can further increase stress and thermal movement in installations.  Additionally installing stone, large format tile or panels in dark colors (ie: absolute black granite tile), increases the chances for thermal growth and shrinkage cycles, due to the increased surface area and darker color (passive solar heating/gain).

Using highly “deformable” two-part acrylic mortar system, such as MAPEI’s Kerabond(T)/Keralastic™ System (ISO 13007 C2ES2P2) this two-component liquid-latex system, creates a stronger deformable mortar that can twist and elongate through cycles of thermal growth and shrinkage.  Wherever you have the potential for increased ‘cycles of movement', either from thermal expansion or shrinkage, or deflection—a two-component liquid-latex is preferable.  In addition to selecting the more ‘deformable’ mortar to accommodate the thermal expansion and shrinkage, ensuring ‘movement joints’ are part of the installation (See the Tile Council of North America (TCNA) EJ-171 for guidelines in placing movement joints).  Always keep in mind that even indoors thermal growth and shrinkage can occur, such as in sun rooms, where tile or stone is going to be directly heated by the sun shining in on the tile or stone.

The following are some helpful tips when installing mortars and grouts during hot weather conditions:
1. Store bags in the shade or, ideally, at room temperature, 75°F – 85°F 24 hours prior to the start of the installation.
2. Mix the mortar or grout with the recommended amount of water as referenced on the back package label.
3. Mix the mortar or grout with cold water, this will extend the pot life and open time of the product.
4. When grouting pre-moisten the tile work with a damp sponge or towel before spreading the grout on the tile.
5. Always clean the mixing bucket before mixing a fresh batch of mortar or grout.  Leftover mortar or grout on the sides of the bucket can accelerate the setting of freshly mixed mortar or grout.
6. When required to set tile or grout an exterior installation in direct sunlight, adjust the time of application to a cooler or at least shaded time of the day.
7. Avoid prolonged and/or high-speed mixing of the grout. This may entrap air in the grout, and the excess heat created from mixing can accelerate and shorten pot life and set times.
8. Organize the setting and grouting process so that once the mortar or grout is mixed, and ready to go, the application begins immediately and proceeds continuously with as few delays in the process as possible.
9. Always include 'movement joints' in the installation to accomodate thermal growth & shrinkage, even on interior spaces that are exposed to passive solar gain, ie: enclosed sunrooms