A hydrophobic admixture, for cementitious materials such as cement paste, mortar, and concrete, includes solid polymer particles with a coating of hydrophobic agent and surfactant. The solid polymer particles adhere to exterior surfaces of hydrated cement particles in the cement matrix. The solid polymer particles deliver the hydrophobic agent into the cement matrix which is hydrophilic. The hydrophobic agents are distributed uniformly throughout the cement matrix. The solid polymer particles can be crumb rubber particles derived from waste rubber tires, recycled plastics and similar solid materials. The hydrophobic liquid agent is derived from waste lubricant oil, spent motor oil, base oil, esters of fatty acids, vegetable oil and the like. Fine particles such as activated carbon, silica fume and spent catalyst can be employed to fill the large pores or cracks that develop in the cementitious matrix. The cured cementitious materials exhibit high contact angles and high compressive strengths.