Type S mortar: minimum 1,800 psi at 28 days per ASTM C270. Proportion specification: 1 Portland cement : 0.5 hydrated lime : 4.5 sand. Property specification: min 1,800 psi, max 12% air. Uses: below-grade masonry, foundation walls, retaining walls, structural masonry, areas subject to high lateral or compressive loads. Good bond strength and durability. Mixing: combine dry ingredients, add water to achieve proper consistency (8-10 in slump). Use within 2.5 hours of mixing (or 1.5 hours in hot weather). Do not re-temper after initial set. Mortar joints: concave or V-joint tooled for weather resistance. CSI 04 05 13. Cost: pre-mixed bags $6-$10/80lb bag. Coverage: ~35 standard bricks per 80lb bag. Types (by strength): M (2,500 psi), S (1,800 psi), N (750 psi), O (350 psi).