I have a patio that's a slab on grade the had 4x8x16 block cemented on edge and used as the sill for screening. Most of the blocks are loose and I'm going to remove them to the slab. I'm re-framing it to enclose the space and using 4x4pt as sills which will be anchored to the slab. The slab has some unevenness after the removal of the block. I've hammered up as much of the old mortar to level it out. I'll use sill seal under the 4x4s but I'm still concerned about any gaps under. Any recommendations for getting the best seal? Skim coat with mortar, lots of silicone or is there a right way to do it?