The subfloor is the structural surface underneath your floor. In most South Florida homes that means a concrete slab. In upper levels and some older properties it is a wood based deck.

Whatever is going on top of it, the subfloor has to be smooth, level, dry and stable first. Every flooring material transfers what is underneath it up to the surface. A dip in the slab becomes a soft spot underfoot in vinyl plank. An uneven area under tile means cracked tiles and loose grout within a year. Debris left behind under laminate shows up as a lump you can feel through the plank.

Preparation is the work that removes those problems before they become permanent. Depending on what the inspection finds, it can involve cleaning the surface down to bare substrate, patching holes and cracks, sanding high points, leveling low areas with a compound, and dealing with moisture or structural issues where they exist.

Moisture is the part that matters most here. Concrete slabs sit directly on the ground and can carry moisture up from below. In a humid climate that is a constant condition rather than an occasional one, and it has to be identified and addressed before a floor goes down over it.