We have a 1989 house that is slab on grade, but not a monolithic pour. So there is a gap all around exterior walls where slab and foundation meet. There is dirt and sometimes the occasional 12" sprout, that shows up in a day in this crack. It's as if the slab shrunk away from the foundation. I am going to scrape and shop vac and wash these cracks, then dry thoroughly. My question is what would be best for filling these cracks? A flexible caulk type sealer, or a hard concrete or epoxy product? Thanks for all input on this one.....