Page 134 - Masonry and Concrete

Understanding Masonry
133
UNDERSTANDING MASONRY

A brick masonry expansion joint is a continuous, open joint with-
out mortar that is designed to accommodate the natural expansion of
brick. Unlike control joints in concrete masonry, expansion joints in
clay masonry are intended to allow the adjacent units or wall sections
to expand without pushing against each other. Because brick masonry
always expands more than it contracts, expansion joints must be free
of mortar or other hard materials. The walls of residences are relatively
short in length compared to most commercial construction, so there is
less accumulated expansion to accommodate. However, stress buildup
can occur even in small structures if the expansion is not properly
accommodated. One of the most obvious results of brick expansion
occurs at the slab corners. The slab is made of concrete, which shrinks
just like concrete masonry. At the same time, the brick is expanding so
the two elements are trying to move in opposite directions. If the brick
is not separated from the concrete by a flashing membrane or other
sheet material, the expansive movement exceeds the tensile strength
of the concrete, and the corner of the slab breaks off.
Despite common misusage, the terms control joint and expansion
joint are not interchangeable. The two types of joints are very different
both in the way they are constructed and in the function they serve.
Several different forms of control joints and expansion joints will be
discussed in Chapter 5, along with tables and rules of thumb on where
to locate the joints in relation to windows, doors, and other building
elements.

Apply Coatings: Most masonry materials do not need any sort of
protective surface coating, and therefore require little or no mainte-
nance for the first 20 to 30 years after construction. Concrete masonry
units, however, can be very absorptive and in most climates will pro-
vide better moisture penetration resistance if they receive a protective
coating. The most commonly used coatings are clear water repellents
which must generally be reapplied every three to five years, depend-
ing on the coating manufacturer’s recommendations, and paints
which usually require recoating at about the same intervals. Decora-
tive concrete block or “architectural” block are available from many
manufacturers with an integral water repellent treatment which is
claimed to last the life of the units. This eliminates the problem of
coating maintenance but complicates the attainment of good bond

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