When the mortar color does not meet expectations, the designer's vision is compromised. One undesirable color variation in masonry mortar joints is surface "mottling." Nick Blohowiak, eastern regional sales manager for SPEC MIX Inc., recently shared some insight into what causes this issue:

Surface mottling of masonry mortar occurs when on-site conditions and construction practices cause the extension or premature termination of the cement hydration. Densifying of the mortar at the surface of the mortar joint during finishing practices also can cause this surface condition. Hydration of portland cement cannot proceed if water is unavailable making the mortar joint darker than desired. Conversely if additional water is available during the curing process the cement can over hydrate yielding a lighter than expected result. Generally, the higher the water content in the mortar, the lighter the mortar. Mottling can manifest itself across the entire surface of the mortar joint or even in small irregular patches.

For Blohowiak's suggestions on how to minimize the problem Read More