Construction Methods Using Dry Stack Concrete Blocks

Concrete Footing

• Dry-stacking starts with building a solid concrete footing for the wall, with steel reinforcing bars set into the concrete 4 feet apart, spaced so holes in the blocks will align over them. Make sure there is rebar at every corner or wall end and any window or door location. Use blocks with solid ends, rather than indented ends such as those used on mortared wall.

Mortar the Base Blocks

• Let the concrete cure for a week before stacking. Even with dry-stacking there is some mortar -- the first or base layer of blocks has to be set on the footing in a bed of mortar and leveled, but with block edges firmly together without any mortar. That base layer must be straight along the wall with the block tops level. Blocks must be set through holes over the reinforcing bars where they are installed.

Edges Together and Overlapped

• Blocks must be set with edges firmly against each other, with no space in between. It is best to work from end to end and set the last block in a row in the center to keep the wall from waving. Block must be overlapped, so each one sets half a block across two other blocks. That is done with a corner block at a 90-degree angle where two walls meet or by starting every other course of a straight wall with a half-block.

Horizontal Reinforcing

• For a wall more than five blocks high, use a special block for the fifth course, which has a slot in the top to accommodate a horizontal reinforcing bar the length of the wall. Put corner anchors at 90-degree junctions by drilling a hole in the joint big enough for a foot-long section of rebar, which goes from one block into the cavity of the abutting block.

Grouting

• Once the last course of blocks is placed, pour concrete grout into all the corner or end openings and every hole with rebar. Fill other openings with sand or grout, to make the interior of the wall solid. Add a cap or "bond beam" of cement to seal the top of the wall. Insert any roof truss or rafter ties into the bond beam.

Surface Cement

• Cover both sides of the wall with surface bonding cement, a special type that is reinforced with fiberglass, 1/8-inch thick. Make sure the cement fills any small cracks or crevices in the blocks. Spread it with a trowel. After a wall surface has been covered with a flat layer of cement, a finish layer can be added to provide any desired texture. The cement needs to be kept moist for a few days while it cures.