Building Foundation Block Materials

Basics

• Concrete blocks used for foundation construction are precast. This means they are poured at the factory into identical block shapes, usually about 8-by-16 inches, though other dimensions are possible. These blocks are brought to the job site and placed in the foundation. This method assures uniformity in block appearance and strength. The curing and drying of the concrete has largely been accomplished at the factory. This does not eliminate the settling and further drying of the block, but this makes it far less amenable to shifting later on as it dries.

Portland

• The concrete block is made largely from a mixture of Portland cement, calcium and silicates. Portland cement is the strongest and most pure form of cement that is normally required for “cement” to be given the name. Portland is largely a limestone and clay mixture that is pulverized. It is then mixed with iron, aluminum, shale and shells. In general, the lime and silica content make up about 85 percent of the mass.

Grouting

• The best block materials used for foundations are grouted. Similar to a heavy glue or mortar, this grout is a mixture of water, clay and sand that is used to further strengthen the block once it is completed. It is nonmetallic and is designed to inhibit shrinking or other distortions once in the ground. Prior to grouting, some companies will add gypsum to the mix to emulsify the entire mixture and make it more amenable to later grouting.

Blended

• Some precast blocks are blended with other materials for the sake of greater strength, heat resistance or frost resistance. Fly ash is added to some mixtures to prevent any chemical variation in the final compound. One method to create a stronger block is to ground the ingredients into a very fine but dense powder. In general terms, when the ingredients are ground finer, the block gets stronger. It must be grouted after this and is a bit more expensive than the lower grade blocks. This type of concrete block might be useful in areas where winters are intense. Block foundation materials are damaged mostly by frost and temperature changes over time, and the different grades of concrete compensate for this.