Block Masonry

Concrete blocks are used for housing, porch, step, and wall foundations because they can yield superior foundation walls so long as they are installed correctly. Regardless of the end use, a concrete block wall must have a supportable footing. Concrete and things made from concrete or cement tend to have fantastic compressive strength, often measured in the thousands of pounds per square inch range.   But the same material typically has only one-tenth the strength when you apply a tension or stretching force to it. Bending a concrete block wall creates tension. Backfilled soil against a wall produces tension as the soil pushes against the wall. Poor quality soil creates tension on a foundation as more and more weight is added to the foundation as the house is built.

There are many variables that control the overall strength of cinder block foundation walls. Design strength of the concrete, concrete blocks, and mortar are very important.  The thickness of the wall with regard to its height is also extremely important. Reinforcing steel is used to strengthen concrete block walls. First, horizontal steel bars or wire fabric are placed in the mortar joints between layers of concrete block to help prevent vertical cracks in the wall should the wall drop or heave.   Second, vertical reinforcing steel should be placed in the hollow voids of the concrete blocks filled with cement grout or pea gravel concrete.

A wall built with cinder concrete blocks or poured cement will not be waterproof.   To maintain dryness inside, the application of a foundation waterproofing system to the exterior of the walls is necessary.   In addition, a drain piping system needs to be installed at the base of the wall adjacent to the footer and covered with three feet of washed gravel. The gravel is then covered with a sheet of tar paper before dirt is placed over it to prevent the backfill dirt from clogging the gravel. The water that flows through the soil and makes it to the pipe is then drained to daylight if the house is built on a sloping lot and if the house is built on a level lot the drain pipe often empties into a sump pit.

 



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