Preconstruction treatment refers to treatment performed prior to or during construction. Just before the concrete slab is done. Basically, a preconstruction treatment is the same as an existing structure treatment with the following exception: treatment is performed to certain surface areas' prior to the pouring of concrete footings and slabs (floors, stoops, patios, walkways, driveways, or etc.) over the surface area. You can forget treating the soil under a footing after the footing is poured. If you have to drill-treat floors, stoops, patios, walkways, driveways, or other obstructions, you are performing an existing structure treatment, not a preconstruction treatment.