What Causes Caulking to Be Squeezed Out of a Brick Wall?

Posted by in Masonry | December 07, 2012

Have you ever seen the soft joint sealant (sometimes called caulking) squeezed out a joint in a brick wall?  (See photo above).  As a structural engineer, I have noticed this innumerable times.  Now you know what we dull engineers do when we are out at a mall or downtown or anywhere that there are buildings – ever looking, ever trying to learn.  But I digress.

Industry studies have shown that the materials in common clay brick are such that it is continually (not continuously) absorbing moisture.  The absorption of moisture over its life, causes the brick to swell.  The increased size causes a brick wall to grow in height and length.

The absorption in moisture begins as soon as the brick leaves the kiln where it was fired.  The brick, having been dried thoroughly by the heat of the kiln, starts absorbing moisture as it is drier than the surrounding air.  As time goes on, the brick approaches equilibrium and the rate of absorption slows, but studies show that it never really stops.

Industry studies have also shown that the materials in some common clay brick are such that the brick expands when heated, but it does not necessarily return to its original size when it cools.  This ratcheting mechanism also causes the brick to become larger.  The increased size causes a brick wall to grow in height and length.  This phenomenon is usually most noticeable on south and west elevations of a brick walled building.

If gaps are not built into a brick wall to accommodate the swelling and expansion, the wall usually exhibits cracking, bulging, crushing, etc.  These gaps are called expansion joints.  The width of the expansion joint should be based on the length of the wall between the these joints and the expansion properties of the brick.  If the joints are not wide enough or spaced too far apart, the result is the bulging out of the sealant, similar to the squeezing of toothpaste out of a tube.

These phenomena are usually not observed in older buildings (pre-World War II), because the lime mortars were much softer then and each vertical joint between the bricks often accommodated the growth of the adjacent brick unit.  The stronger and harder cement mortars of today are not as forgiving or helpful.

In this case it is true, “They don’t build them like they used to.”

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