The Bureau of Mines conducted laboratory tests to determine the effects of the physical properties of coarse coal waste of adding large amounts of fine coal waste. Maximum laboratory dry density, optimum moisture content, shear strength, and permeability tests were conducted on samples that contained 18 to 60 pct minus No. 4 (U.S. standard sieve size) coal waste. For the nonslaky materials, maximum laboratory densities were highest and permeabilities lowest when the samples contained between 30 and 40 pct minus No. 4. Shear strength increased rapidly when the proportion of minus No. 4 Was increased from 20 to 40 pct, but then increased only slightly or leveled off when the minus No. 4 Was increased to 60 pct. Optimum moisture content and permeability were the physical properties most affected by the addition of fines. Optimum moisture content increased as much as 3 pct, and permeabilities decreased up to three orders of magnitude. Slaky coal waste material had physical property reactions to the addition of fines substantially different from those of nonslaky material.