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An analysis of variance was used to evaluate quantitatively the effect of a new type of mela-mine resin admixture, a 20 percent aqueous solu-tion of a sodium salt of a special polymerized product of melamine and formaldehyde, on the setting, water-reducing effect and the compressive and flexural strengths of mortars made from ground clinker and portland cement. This resin greatly increases the retarding action of gypsum, acts as a powerful water-reducing agent and, above all, increases the compressive and flexural strengths by up to 150 percent for mortars of ground clinker and by up to 65 percent for mor-tars of portland cement. The maximum effect is obtained when 6 to 9 percent resin is added, though little additional improvement is achieved above 5 percent. [ABSTRACT FROM AUTHOR]