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
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.