I cracked a red brick open and found it to be gray on the inside. Is this a problem?
"Just because the brick is gray on the inside doesn't mean you have bad properties," says Dr. Gilbert C. Robinson of Clemson University. "Color alone doesn't tell whether it's good or bad." A gray color on the inside of brick may suggest incomplete firing or not enough oxygen at a certain firing stage. To verify that the brick was properly fired, have it tested in a lab or ask the brick manufacturer for test results. If the properties of the brick meet minimum requirements, the brick is acceptable.