A specification requires us to use "dry pack" mortar to fill deep holes in a concrete wall. What is dry pack mortar and how is it installed?
Dry pack mortar is a stiff sand-cement mortar that is typically used to repair small areas that are deeper than they are wide. According to the Bureau of Reclamation's Guide to Concrete Repair, dry pack mortar contains (by dry volume or weight) one part cement, 2 1/2 parts sand, and enough water to produce a mortar that will just stick together while being molded into a ball with the hands. The ball should neither slump when placed on a flat surface, nor crumble due to lack of moisture. Place dry pack mortar immediately after mixing it. Compact the mortar in the hole by striking a hardwood dowel or stick with a hammer. The sticks are usually about eight to 12 inches long and no more than one inch in diameter. Use a wooden stick instead of a metal one because metal tends to polish the surface of the mortar, making bonding less certain and filling less uniform. Place and pack the mortar in layers to a compacted thickness of about 3/8 inch. Direct the tamping at a slight angle toward the sides of the hole to ensure maximum compaction in these areas. Overfill the hole slightly, then place the flat side of a hardwood piece against the hole and strike it several times with a hammer. If necessary, a few light strokes with a rag may improve its appearance.