On a 1970s parking structure last month, I paired a Hilti PS 300 ferroscan with a 2.6 GHz GPR antenna to map top mats before coring; we cut cores by about 60% and preserved load paths. For dense bar grids in 8–10 in slabs, what scan spacing and depth calibration have given you the most reliable cover and bar size, and do you trust UPV as a cross-check so we avoid unnecessary FRP or section enlargement and the embodied carbon that comes with it?
On a 70s garage we ran 2 in raster both directions with the 2.6 GHz and set dielectric from a slab-edge thickness read (about 6.8), which kept cover within about 1/4 in; ferroscan called bar size well when cover <2.5 in, otherwise we bracketed #5–#6… I don’t use UPV to confirm bar geometry — “stethoscope, not X-ray” — just to flag delams and pick one short core to lock permittivity; @OP do you have an edge or drop panel to calibrate on?
Agree with @jameson_riley92 on setting εr off an edge thickness — then refine with a hyperbola fit on a known tie wire; with a 2.6 GHz I’ll run 1.5 in raster near beams and 2 in in the field, which keeps cover within about 1/8–1/4 in. On the PS 300, use double‑layer mode and do a quick size calibration off one exposed bar so the dense grids don’t merge. UPV’s a “stethoscope, not an X‑ray” for this — use it for uniformity, but for cover/size I’d trust impact‑echo or a small pilot hole instead.