Subject: Getting Approval
Several times lately, the question of the finished appearance of masonry has come up. Everyone seems to be trying to find something that will help them sell their work. I decided that I may as well jump into the fray one more time. As I have stated many times before, there is no ASTM standard that addresses workmanship of the masonry craftsman and any allowable tolerances.
There are many reference documents that include tolerances but they must be included in the project specifications or notes. Then there are tolerances in the TMS 602 that can be used but they are for structural use and could not be totally acceptable for the finished appearance.
But really, what are tolerances? Tolerance is the deviation from an exact dimension or location that masonry units or joints that can vary and still be considered exact. So much so that an outside corner could be +/-1/4” in 10’-0” and still be considered plumb. So, according to several reference documents plumb may not be plumb and level may not be level.
A given measurement may not be the exact dimension given. So if there are no references to tolerances in the specifications, what is a person going to do? First, check the specifications very closely. The architect could say to install the masonry “plumb, level and true to a line.” They could also give joint sizes. I have seen specifications that said that the head and bed joints shall be 3/8”. Well now, can a mason install masonry units plumb, level and with all joints being 3/8”? The short answer is NO.
Using the 4” modular system that masonry is based on the units being 4”,8”, 12”, etc., including the mortar joint. Since the standards for masonry units have an allowable variation in size, the joints typically will not be 3/8”. They will be close but not exact. There are some brick sizes that do not stay with the 4” module and have their own separate considerations.
With most brick, the length is closer to 7 ½” than 7 5/8”. That means the head joint will be 7/16” or ½” in size or whatever it takes to accommodate the variation in size. CMU is typically a little more consistent in size and will have fewer joints to keep in line. If the architect doesn’t use good modular dimensions you may have to vary the head joints to make the dimensions given.
In any case, the head joints should be consistently the same size. What does that have to do with keeping the head joints plumb and straight? Unless the masonry is called out as a stack bond or one of the beautiful architectural bonds, the bond will be running or half bond. This is simply the center of each head joint that is at the center of the unit below.
Even though at corners and openings you gain or lose a head joint because of required dimensions, the main consideration is that all joints are consistent in size and centered directly over the one below. But we need to remember that plumb, level, straight and true to a line are not the only considerations for acceptable workmanship. There are many other considerations that are involved.
As I have said many times before an approved mockup is one of the best tools you can use. It can be free standing or on the wall. The main thing is to get the approval of your workmanship and procedures before you start. Then simply build another beautiful masonry building. Be safe.
Remember to raise the line and come on around the corner.
Jerry Painter, FASTM