On a recent project, I specified the use of Neoprene foam fillers for expansion joints in the clay masonry walls. The contractor, however, installed solid Neoprene control joint fillers like those typically used in concrete masonry walls.

Is this substitution acceptable?

Solid Neoprene or other plastic expansion joint materials used for concrete masonry control joints are not appropriate for use in clay masonry. Concrete masonry typically shrinks over time as it dries to accommodate the environment. The control joint materials are relatively stiff to assist in aligning the concrete masonry on either side of the joint and possibly for transferring out of plane loads across the joints.

These joints are not intended to absorb expansion. Since the concrete masonry shrinks, and this drying shrinkage is generally more than the expected thermal expansion, the material does not need to be very compressible.

Clay masonry, on the other hand, expands over time from moisture expansion, as well as from thermal expansion. Consequently, the material used in the expansion joints must be highly compressible.

The Neoprene foam joint filler that you specified was highly compressible, yet at the same time can prevent mortar from squeezing out of the bed joints and bridging the expansion joints during initial construction. It would have been a much better material.

Still, I typically do not recommend using fillers of any kind in vertical expansion joints. I prefer leaving vertical joints open so that they can be visually inspected to remove any mortar bridges that occur during construction.

When fillers are used, mortar may squeeze across the expansion joint at a filler joint, which would bridge the expansion joint locally at these points. By requiring that the joints be inspected and all mortar bridges removed immediately following construction, there is confirmation that these joints are completely free of mortar and debris throughout their height.