My back yard is mostly a pool and a concrete deck with brick strips. It has been in place since 1994 and over the years the concrete has shifted ever so slightly so there are small gaps (1/16") between the bricks and the concrete. Weeds grow out of these gaps. I need to re-caulk the pool and I thought it would be a good time to seal the gaps also. I plan to use SikaFlex Self Leveling polyurethane sealant and I also plan to saw each gap to about 1/8" wide. My question is this: 1-what herbicide can I use that will not leave any oily/hydrocarbon residue? Any contamination will prevent the sealant from adhering properly. 2-what herbicides last the longest ? I am assuming that these weeds only grow because the wind gets a seed in the gap. The sealant should stop that from happening.