The architect for the project I am working on has selected a molded brick with a frog. In laying this brick, should the frog be placed up or down?
Currently, there is no industry consensus on how to lay a brick unit that has a frog. A frog is a depression in one bearing face of a molded or pressed brick. The frog reduces the weight of the brick and makes it easier to remove from the forms. ASTM specifications C 62 (building brick), C 216 (facing brick), and C 652 (hollow brick) all set limits on the size of frogs. Frogs can't be closer than 3/4 inch to any edge of the brick. Frogs greater than 3/8 inch deep at any point are treated the same as cores. Frogs less than 3/8 inch deep don't affect the net area of the unit. Some experts say that bricks containing frogs should be laid with the frog up so that the frog is completely filled with mortar. If the brick is laid with the frog on the bottom, the frog may not get completely filled with mortar. This would make the brick wall only face-shell bedded, which produces less wall strength than full mortar bedding. Other experts say brick should be laid with the frog down. They give two reasons. First, a uniform bed of mortar can be laid more easily on the face that doesn't contain the frog. If the frog is less than 3/8 inch deep, the mortar bed should be able to fill the frog. Second, if the frog is laid up, it can hold water, which may contribute to early brick deterioration. Most masonry walls built today are not highly stressed bearing walls. Water penetration and resulting freeze-thaw damage are greater problems. Thus, I recommend laying brick with the frog on the bottom.