What Is the Ratio of Water to Mortar for Thinset Tile Installation?

Thinset is a cement-based glue beneath tile that bonds or sticks the tile to the surface substrate. Thinset is composed of lime and additional bonding agents, giving it its signature tile-bonding bite. Thinset contains harmful silica particulate. Do not breathe thinset dust; wear a dust mask while mixing the material.

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Bathroom tile is installed with thinset.

Water Mixing Ratio

Thinset is available in powder form in both 25- and 50-lb. bags. The ratio of water to mortar for thinset tile is 6:50 or 6 qts. of water per 50-lb. bag. The ratio for a 25-lb. bag is 3 qts. of water per 25-lb. bag, or 3:25. Thinset manufacturers recommend mixing thinset to a pastelike, creamy consistency. Use clean water only (debris- and sediment-free). Do not use warm or hot water for mixing thinset. Warm water causes thinset to set up too fast.

Admix Ratio

Thinset manufacturers recommend substituting a polymer thinset admix for water for vitreous and impervious tile such as porcelain, glass, terrazzo, natural stone and brick tile. The admix-to-thinset ratio is 6:50 or 3:25, depending on whether you are using a 50- or 25-lb. bag of thinset.

Mixing

For small jobs (for instance, a small backsplash or bathroom floor), mix thinset with a mason's trowel in a 5-gallon bucket. Add a medium amount of powder from a 25-lb. bag, slowly adding water until you reach the correct 6:25 ratio. Mix in a circular fashion; loosen dry thinset clumps on the side and bottom of the pail. For larger tile jobs, use a 1/2-inch electric drill mixer. Attach a mixing paddle to the electric mixer. Mix the thinset in a 5-gallon bucket. Add a portion of the 25-lb. bag first. Place the electric mixer paddle in the bucket. Slowly add water and begin mixing. Add water until you reach the 6:25 ratio and achieve a pasty-creamy consistency.

Application

Use a 1/8- to 1/4-inch notched trowel for thin mosaics and 4-inch wall tile. Use a deeper 3/8-inch notched trowel for large format tile (such as 18-inch or larger). Spread the thinset thoroughly and consistently. For best results, hold the notched trowel at a 45-degree angle while applying thinset. Apply to the immediate installation area only -- do not smear too far ahead. Properly mixed thinset retains a toothlike grid after smearing.

Curing

Thinset manufacturers recommend allowing least 24 hours for thinset to cure before heavy foot traffic or grouting. Not allowing for proper cure time may compromise the entire project. In worse case scenarios, you might even have to redo the compromised area.