Masonry Control Joints

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As hardy Minnesotans, we all understand the extremes of the climate we live in. From the excessive 90 degree heat and humidity of July to the -20 degree January mornings, I think you would agree we live in a very inhospitable climate to most living things.

Buildings must also adapt to this 120 degree temperature swing. Exterior building materials actually expand and shrink along with the weather. In addition, some exterior building materials actually shrink and expand at different rates than their adjacent materials.

Take brick and concrete block (CMU) for instance.  This is a very common building material on commercial buildings and usually you see it with a rockface block close to the earth and brick starting from waist height and continuing up.  Did you know that in the extreme heat of the summer, the block portion of this wall will expand faster and more distance than the brick above it.  If you had a 100 foot wall with no control joints in it, the brick would grow 1/3” and the block wall would grow ¾” to 1 ½”! That’s only part of the problem, in addition to the thermal expansion, over time the wall will grow and/or shrink depending on the material. That same 100’ brick wall will increase in length by ¾”, but the block wall beneath will shrink 5/8”!

That is why you see control joints every 20’ within a masonry wall.  These are vertical cuts in the masonry wall which are filled with caulk.

I would like to thank Matt Figus of RoofSpec for contributing to this blog. If you have any need for a professional to inspect problem roofs or wall cavities, please contact the folks at RoofSpec at 651-639-0644.

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