Concrete-Block Building Techniques

Type of Blocks Affects Building Technique

• While you can build foundations, floors and interior and exterior walls with CMUs, you need to choose the right type of concrete blocks for the purpose. Obviously you don’t want to set corner blocks in the middle of a wall. Bullnose-edged blocks provide curved edges. Control joint blocks work best where the wall needs to be able to shift slightly. Sill and lintel blocks go in doors and windows. Many more types of CMUs are available, each with its own special purpose. Concrete blocks are also created for indoor or outdoor use. Grade “S” is suitable for aboveground use with no weather exposure. Grade “N” blocks are for outdoor, exposed use and may be used both above and below ground level.

Stacking Patterns

• Walls made of concrete building blocks may utilize a number of stacking patterns. Some patterns are easy to stack and take little time to set. Other patterns are more intricate and are more labor intensive to build. Dry stack blocks are one of the most common stacking patterns. This is simply a building technique that lays each successive row on top of the one below it. Other than setting the first row of CMUs in mortar to level them, no bonding agent is used between the blocks. Once the blocks are set, both sides of the wall are covered with fiber-reinforced surface bonding cement that binds the blocks together. For structural stability, it’s necessary to stagger courses of blocks when they are set in mortar. It’s possible to stack similarly sized blocks to create a running pattern. Stacking patterns utilize different sized blocks for each course.

Horizontal Reinforcement

• Depending on the stacking pattern and the placement of wall joints, horizontal reinforcement may be necessary in the walls to keep them from bowing under the force of the ground outside the foundation. Horizontal reinforcement also is necessary when tying two walls together. Pieces of wire are welded together to create a ladder-like form. One of these metal units is set on top of each course that is below ground. For walls above ground, metal reinforcement goes between every second or third course of blocks.

Vertical Reinforcement

• Vertical reinforcement allows the cement blocks on the base of a wall to support a greater load, allowing you to build taller walls. Reinforcement bar, or rebar, is set vertically inside hollow CMUs. Concrete mortar is then poured into the hollow areas setting the rebar in place.