We have a project in WPB, the plans are calling out a Compressible Bond beaker at the control joints. We did not include this (Rubber, PVC CJ) in our contract, however, we did account for leaving the 3/8” of an inch as gap the control joint. Our walls are 8” CMU with a 2 hour fire rating.
The EOR indicated that he wanted the joint to be 2 hr fire rated.
My question is what determines the use of a rubber or PVC material verses the 3/8” gap for a control joint?? Are either of these fire rated?
Please see the attached detail and EOR response.
A "compressible bond breaker" in a control joint, as shown in his detail, would mean a backer rod. The backer rod or "compressible bond breaker" is pushed or "compressed" into the joint prior to caulking the 3/8" joint. It's purpose is to control the amount of caulking that goes into the joint, but more importantly, to "break" the 3 point "bonding" that occurs in the back of the joint and thus prevents the caulking from tearing open at this location.
The EOR is confused about the need for a COMPRESSIBLE material. He does want a fire rated system which is not what was called for either in the plans or in his response. His detail does not call out for a key way so that is clear. But it simply does not indicate what he is asking for. The language, as I have said, is simply another way of asking for a backer rod which he has already shown. He needs to go to https://submittalwizard.3m.com/# and pick a caulking that will give him the 2 hr rating he desires. A piece of "compressible rubber" does not carry a 2 hr fire rating. Whatever is in the control joint does NOT have to be compressible because the joint will never be compressed. Conc masonry walls shrink - always. He may be thinking about a clay brick product that would be EXPANDING and thus compressing the joint. You can fill masonry control joints with mortar if you want because they DON'T COMPRESS. Brick expansion joints have to be completely clean of mortar because the wall expands and the joint does get compressed.
At this point he could solve the problem by simply changing to a fire rated caulking and eliminating the rubber filler. What he is asking for in his response carries no fire rating and is not what the words on the plans say.
Another solution would be to provide a min of a 2" deep mortar joint on each side of the wall. After raking out the mortar for your backer rod and caulking you would have the usual 1 1/4" of mortar left in the joint - the same as every other head joint in the wall. This would meet the 2 hr rating by simply matching the amount of mortar as every other joint in a typical 2 hr masonry wall with face shell bedding. You would not have to go to the extra expense of using a fire rated caulking.
I would be happy to discuss this with the EOR. Proper control joint construction is an area of common misunderstanding. It was nice to see that he had actually bothered to include control joints, an essential part of preventing random masonry cracking.
Detail for Compressible bond breaker detail.docx
Jerry Painter, FASTM
Don Beers, PE, GC