A survey and test program was conducted to establish from materials now in use or available the best sealants for concrete block stoppings and the value of squeeze blocks for stoppings with mine convergence. Mines were surveyed for sealants currently used, and commercial products were surveyed for new sealant materials. An in- mine evaluation showed that, within limits, poor stopping construction practices rather than sealants were the cause of leakage. Sealants were found that could be brushed on concrete blocks rather than troweled to produce stoppings twice the strength of mortared joint stoppings, and equal in strength to dry-stacked stoppings, both standard construction techniques. The brush-on technique and improved construction practices were proved on demonstration stoppings tested over a period of 1 year and are now recommended by the Bureau of Mines in a new handbook. Polystyrene boardstock was the most commonly used material for squeeze blocks and was considered by mines using squeeze blocks to be helpful in maintaining stopping integrity under mine convergence conditions. Alternative squeeze block materials with overall properties better than polystyrene were found.