Using previous markings as a guide, cut blocks to accommodate window and door openings. Determine buck thickness and rough dimension tolerances. Be sure, when bucks are built, to allow for an opening in the sill for concrete pour.

Bucks can be built from timber or new buck products, made from extruded plastic contain a channel to the exact dimension of the block. Once in place, bucks can be secured using Fiberglass tape or permanent windlocks.