The wetting agent for the grains can be a liquid heathardenable phenolic resin or a resin solvent such as furfuryl alcohol, furfural or cresol or a mixture of these or a solution of thermoplastic polyhydroxyether in an organic solvent such as a ketone as for example methylethyl ketone, tetrahydrofuran, or dioxane, dimethylformamide, dimethyl sulfoxide and the like.