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Q.When rebuilding a chimney above the roofline, is it okay to reuse the existing bricks? I have heard that mortar does not stick as well to reused bricks as it does to new bricks. Is this true?

A.Richard Allen, Jr., staff engineer at the Brick Industry Association, responds: You are correct — salvaged brick normally develop low bond strength when used in new construction. When a new brick is placed in mortar, the pores of the brick absorb the water in the mortar, drawing the cementitious material into the brick. Once the mortar has cured, the cementitious material that has been absorbed into the pores of the brick will bond the brick to the mortar, creating a solid wall.

In salvaged brick, the pores of the brick are, in essence, clogged by the hardened mortar materials, preventing salvaged brick construction from developing the same bond strength as construction using new brick. So, I would be extremely cautious in using salvaged brick. For more information on salvaged brick, you can access Technical Note 15 at www.brickinfo.org.