What size and type backer rod can I use for Movement joints?


New garage floor. Contractor cut break lines 1/8 wide by 1 in deep. 350 lineal feet to fill. I bought Sikaflex 1C SL. I cannot find where 1/8 in backer rod is available. Sika says max depth is 1/2 in. Do I need backer rod or can I just fill the 1 in? It's really slow and tedious to squeeze into a 1/8 cut. Please advise. Thank you.


ANSWER - The closed-cell foam backer rod is suppose to be wider than the movement joint.  You can compress a 1/4" foam backer rod into a 1/8" wide movement joint.

The backer rod serves two main purposes, one that it fills the void so moisture doesn't fill it, and it acts as a bond-breaker so the sealant doesn't bond to it that would limit its performance in stretching and compressing when subjected to various stresses.

I have seen sand used to fill the joint that will act as a bond breaker, but it does absorb moisture.

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