Masonry Magazine August 2006 Page. 25
Take a moment to look at the four groupings of colored mortar channels pictured above. How many colors do you see? Although there are 12 total channels, there are only four different colors. Each of the four sets of mortar channels represents one color. Each of the color sets meets the fundamental requirements to maintain color uniformity. They are:
Sand from the same source
The same cement/lime or prepared masonry cement
The same pigment and a uniform measurement from batch to batch
Furthermore, the color sets represented are each formulated with the same amount of sand, cement and pigment. As evidenced, this alone does not ensure uniformity in color. These samples demonstrate that water demand and striking times matter.
Water Demand
WATER DEMAND in masonry mortars is going to be a function of the mason's needs. How loose or stiff a mortar is made will be a function of the masonry unit. With this said, brick that has a high initial rate of absorption (IRA) requires a "looser" mortar, a hard brick requires a stiffer mortar. A glazed brick also requires a stiffer mortar, as there is limited ability to draw out and suck moisture from the mortar. Meanwhile, block mortar needs to be wet enough to be workable and carry the weight of the block.
Water demand will vary due to daily weather conditions. Cool mornings require a mortar that is a little stiffer. As a warm day develops, water demand will increase. For these reasons, a prescribed amount of water cannot be necessarily adhered to. Due to varying water requirements, it is important to tool the joints when the mortar is thumbprint hard.
Striking Times
IN EACH GROUP, the center channel is the correct and desired mortar color. The center channels were struck when the mortar was thumbprint hard. A mortar joint that is struck, or tooled, at this time seals the joint with a slight paste, thus closing the mortar joint to water and weather penetration.