Concrete blocks are made in sizes which are always in fractional form.The reason is that the standard mortar joint is 3/8 inch in size and when added to the block dimensions this will come out an even number. For instance a standard stretcher block is 15 5/ 8 inches long. with a 3/8 inch mortar joint this gives an even 16 inches.This makes it easier to calculate the quantity of blocks needed for a job and makes walls an even number in height and length.
Concrete blocks are made in both heavy and lightweight types and in full length and half length sizes.The half lengths are necessary so that the joints in a wall can be offset by a half block length to ensure stronger construction.
The most commonly used block is the stretcher block which is nominally 8 inches by 8 inches by 16 inches in size. It has three hollow cores to make it lighter and to save on materials. The heavyweight block weighs 43 to 50 lbs as a rule. The lightweight block which is used only for non load bearing construction is about 10 lbs lighter.
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