Clay Brick Expansion – It is Real

Posted by in Case Studies, Cracking, Masonry | April 20, 2020

I just attended a webinar about movement joints in masonry.  The topics included the different types of movement joints (isolation, expansion, and contraction); why the need for movement joints; and where to place movement joints. 

I’ve been designing, detailing, and diagnosing movement joints for over 45 years now.  My experience with these began in the 1970’s when I was diagnosing failed masonry joints, analyzing what movements had occurred and/or what movements to expect, and then designing and detailing the appropriate movement joints. 

Since I have been aware of proper joint placement for 45 years, I often wince when I see the movement joint types and placements in the masonry walls while vacationing, shopping, walking, driving, etc., especially when accompanied by the appropriate cracking pattern that shows the proper joint placement.  (As one of my favorite detectives would often say, “It’s a blessing and a curse.”)

It seems that although there are basic principles that can be applied to evaluate the internal movements of masonry, such as, thermal and moisture variations, the masonry industry is ever learning.  Much of the learning is required because architects and masons (when there is no architect) discover and/or invent materials, methods, and wall systems that are faster, easier, and less expensive to construct.  These discoveries and inventions often increase the movement and stresses on the masonry units and/or the mortar.   

In the case we consider today I will provide a few basics.  Brick masonry requires regularly spaced joints to allow for the expansion of the clay brick material.  Brick industry standards currently recommend spacing expansion joints at no more than 20 to 25 feet and half that distance from the corners.  The recommended thickness of an expansion joint is generally 3/8 to ½ inches.  The expansion joint is to be clear of any hard material, such as mortar and may be finished at the surface with a recessed foam backer rod and a flexible sealant (soft caulking).        

Now, for our case study.

The brick veneer for the subject dwelling in the featured photograph measured approximately 64 feet long.  If one is to space expansion joints at 25 feet and half that distance from the corners, there should have been at least three vertical expansion joints, but none were provided. 

And, since there were no expansion joints in this veneer it expanded outward at the end (Figure 1), slid horizontally in-plane (Figure 2), and cracked and shifted outward near the base (Figure 3).

Figure 1 Brick veneer expands beyond face of rear wall.
Figure 2 Upper brick slides to the left as it expands.
Figure 3 Horizontal cracking along base from upper brick expanding. Lower brick restrained by concrete block basement wall backup.
Figure 4 Upper brick shifts off lower brick during repeated thermal expansion and contraction.

As you can see, clay brick does expand.  I’ve seen it hundreds of times.

Please, install expansion joints in clay brick masonry veneer.  For more information see Accommodating Expansion of Brickwork, Tech Note 18A by the Brick Institute of America. 

And by the way – that detective I spoke of previously is Monk.