Dry Stack Block Wall Problems

Concrete Base

• Dry-stacked walls must be built on a solid concrete base or they will not be stable. Dry-stacked block walls also need vertical reinforcing bars at key points. These should be located before the foundation is poured, so they will be secured in the concrete. Blocks must be laid over them with the rebar through the hollows in the blocks.

Rebar Placement

• Rebar must be placed correctly, at corners or ends of walls, around any door or window openings and generally every 4 feet of wall. Failing to plan rebar will result in problems later. Load-bearing walls often need horizontal as well as vertical reinforcement to conform to building codes. This requires using special blocks made with openings for horizontal bars, or you'll have to cut slots in the bottoms as blocks are stacked.

First Course

• The first course of a dry-stacked wall is set in mortar and must be perfectly level and straight. Only the bottoms of the blocks are set in mortar; there cannot be any mortar in the vertical joints between blocks. Failing to level the first course will throw the entire wall off. Since foundations are rarely perfectly level, the base mortar has to be used to level the tops of the first blocks.

Square Corners

• Corner and end blocks must be accurately placed. Dry-stacked blocks are laid in a running bond, so each block overlaps two others by half a block. Special end and corner blocks are solid on the outer edges, so the cemented wall will have a solid surface. Corners where walls meet must be perfectly squared or both walls will be off.

Constant Leveling

• Blocks have to be laid on top of the base course to match exactly to keep the wall straight, level and plumb as blocks are added. This requires care and constant use of a level to keep the dry stack correct. Any deviation will weaken the finished wall. Blocks must be dry-stacked over the vertical rebar and adjusted in place.

Surface Bonding

• Surface bonding cement has to be mixed properly. If it is too thin, the fibers in it will protrude and spoil the surface appearance as well as weaken the cementing. It needs to be spread at least 1/8 inch thick, on both sides of the wall. Blocks also need to be dampened before cement is applied; failing to do so will result in a weaker cement bond.

Grouting

• Filling block holes with concrete or grout is another must. Each block that has rebar in it needs to be filled with concrete or grout from the foundation to the top of the block. This filling has to be tamped with a long board or other tool to make it solid from the base up. Leaving gaps in the filling will weaken the wall.