I have been in the masonry business for some time but was recently stumped when asked for the C/B ratio for our brick. What is a C/B ratio?
The C/B ratio is short for cold water/boiling water absorption ratio, which is another name for the saturation coefficient. It's an indicator of brick's resistance to freezing and thawing. To calculate the saturation coefficient, cold water absorption and boiling water absorption are measured. Samples of the brick are oven dried and weighed. Then they're submerged in cold water for 24 hours, surface dried with a damp cloth, and weighed again. The weight of water absorbed is divided by the oven dry weight and expressed as a percentage. The same samples are next submerged in water, heated to boiling, and boiled continuously for 5 hours. After surface drying with a damp cloth they're weighed again. The weight of water absorbed during boiling also is divided by the oven dry weight and expressed as a percentage. The saturation coefficient is the ratio of cold water absorption to boiling water absorption. The test method is more completely described in ASTM C 67, Standard Methods of Sampling and Testing Brick and Structural Clay Tile. The saturation coefficient is almost always less than 1.0, and the lower the value the less absorptive the brick. ASTM C 62, Standard Specification for Building Brick, sets maximum permissible values for brick that will be exposed to freezing and thawing. However, these requirements may be waived if the brick passes a freezing and thawing test, also described in ASTM C 67.