FlexBond is a mortar mix manufactured by Custom Building Products with added polymers used for setting ceramic, porcelain, natural stone and glass tile. Polymer mortars have additives that give them added strength and flexibility. This allows them to move slightly without breaking the bond between the tile and the underlayment. According to Custom Building Products, FlexBond can isolate the tile from cracks up to 1/16 inch wide in the substrate surface, a property usually not attributed to mortars. FlexBond is mixed and spread in a fashion similar to other tile mortars.
Add 2.5 quarts of water to the 5 gallon bucket. Pour one-half of a 50 lb. bag of mortar into the bucket.
Mix the mortar with a mortar paddle and a drill set on low speed. Optimal speed for mixing is 100 to 150 RPM. If necessary, add water while mixing -- 1/4 cup at a time until a peanut butter like consistency is reached. Allow the mortar to stand for 5 minutes.
Mix the mortar again for 1 to 2 minutes at low speed. If the mixture is too thick, you can add tiny amounts of water to reach the consistency of peanut butter.
Spread a thin coat of mortar on the underlayment using the flat side of the notched trowel, pressing the mortar onto the underlayment. Cover an area about 2 tiles deep by 3 tiles wide at a time. This is called a skim coat. Only cover an area 1 tile deep by 3 tiles wide for large tiles greater than 16 inches square.
Place a quart-sized pile of mortar on the underlayment in the area just skin coated. Use the notched side of the trowel to spread the mortar around, covering the same area just skim coated. Hold the trowel at a 45 degree angle to the floor and pull the trowel through the mortar. Spread the mortar so that every tile is fully supported and bonded by mortar.
Remix the mortar occasionally if the mortar begins to skim over in the bucket. Working time for FlexBond in the bucket is about four hours, but the mortar will begin to skim over in about 60 minutes, if it is not used, and remixing will be required. Do not add water while remixing.