Variations in mortar mixing affect mason productivity and mortar strength. What's the right way to mix mortar? PROPORTIONING THE MIX A good mortar mix starts with the basics--the proportions. Contract documents should specify what type of mortar to use: Type M, S, N, or O, as detailed in ASTM C 270. Check and double check that the proportions for the specified mortar are being used. MEASURING MATERIALS Some organizations, including the Brick Institute of America (BIA), do not permit measuring ingredients by shovel. This can be a problem for sand and sometimes for lime. If shovel measurements are not allowed, construct 12x12x12-inch wood boxes to measure the sand in 1-cubic-foot increments. CONTROL THE MOISTURE CONTENT It's easier to produce uniform mortar from batch to batch if the sand is uniformly moist. To help maintain a uniform moisture content, cover sandpiles with polyethylene. MIXING THE INGREDIENTS The way the materials are mixed may vary, but the following order has proved to be successful: Place 3/4 of the water, 1/2 the sand, and all the cementitious materials in the mixer and mix them for a few minutes. Then add the remainder of the sand and enough water to produce the desired consistency.