Masonry Control Joint
CSI Division 04, Masonry
A vertical joint built into a masonry wall at planned intervals, designed to let the wall expand, contract, or crack in a controlled, hidden location rather than randomly wherever stress happens to build up.
Why it matters
Masonry naturally moves with temperature and moisture changes, and without control joints placed at the right intervals, that movement shows up as random, unsightly cracking through the brick or block itself instead of at an intentional, nearly invisible joint designed to absorb it.
On a real project
A long masonry wall includes control joints spaced according to industry guidelines, placed at changes in wall height and near corners, so the wall's natural movement concentrates at those joints instead of cracking through the field of brick or block.
Who this matters most to
A Mason has to build control joints into the wall at the right locations as the wall goes up, since retrofitting one into an already-built wall isn't really possible. An Architect specifies control joint locations during design, coordinating them with the wall's actual geometry rather than leaving it to be figured out in the field.
Where this goes wrong
A long masonry wall is built without control joints at the spacing industry guidelines recommend, in an effort to keep the wall's appearance uniform. Within a year or two of temperature cycling, the wall develops a random diagonal crack through the brick itself, a crack a properly placed control joint would have redirected to an intentional, far less visible location.