Thinset mortar is the cementitious product that affixes ceramic tile to floors, countertops, walls and other surfaces. Like concrete, mortar must cure in order to be an effective adhesive. Properly installed tile is durable, but if you do not allow the mortar to cure properly before grouting, it can crack or crumble, causing the tiles to also crack or become loose.
Time Before Grouting
Drying time varies with ambient air temperature, humidity and moisture content of the mortar when applied. In general, mortar must set at least 24 to 48 hours before grouting.
Apply mortar when the ambient air temperature is between 50 and 100 degrees Fahrenheit. Ideally, temperatures should not exceed this range for at least 72 hours after application. The area should be well-ventilated but not exposed to high wind or heat.
Even when mortar appears dry on the outside edges of the tile, it may not have fully cured beneath the tile surface. Allowing proper time for the mortar to cure before grouting will ensure your tiled surface will last for at least decades.
Setting vs. Curing
Cement-based products must set, or dry, in order to achieve the strength, durability or other conditions for their intended use. These products must also cure, which generally occurs while the product is drying. Curing refers to the chemical processes taking place within the product that allow it to attain the properties required for its intended use. Curing begins as soon as you add water to the dry mortar and continues until the product is completely dry. Maintaining a certain moisture level is required to cure the material.
In addition to cement, thinset mortars may contain proprietary blends of polymers and other chemicals. Some mortars contain ingredients that hasten the curing time, allowing grouting to begin after three hours.
Always follow the manufacturer's directions and wear chemical-resistant gloves and eye protection when handling and mixing mortar. Be careful not to inhale the fine powder, especially when pouring the dry product out of the bag.
Mortar vs. Mastic
Thinset mortar is a blend of cement, sand and other materials that is sold in 25- or 50-pound bags of dry material. The generic term "mastic" refers to premixed adhesives used for various purposes in the construction industry. Mastic for ceramic tile applications uses polymers as the bonding agent rather than cement. Because it is sold in ready-to-use tubs, mastic may be easier to use and clean up; however, it is not suited for exterior use, steam rooms, radiant floors or other applications exposed to water or heat.