Our house was built in 1975 and has, of course, settled a little bit. There are several cracks in the slab. They are very thin and there’s no big displacement. Should I seal the cracks before laying the floor. My planks call for a 6mil poly sheet and I am also using the optional underlayment pad made by the same manufacturer (Corelux). Any recommendations as to which sealant (e.g. Bluestar, Quikcrete, Crackweld)? Thanx!