A solid ¾" hardwood floor will outlive most owners. Done right, it survives 4 to 6 full sandings over a 60–100 year service life. Done wrong — a contractor leaning too hard on the drum sander, or sanding more aggressively than the wear required — and you've burned a sanding in a single project.
The arithmetic of a hardwood floor
A standard 19 mm solid plank has roughly 6 mm of wood above the tongue groove. Below the groove there's nothing to sand — that's the structural bottom. A full sanding removes 0.8–1.2 mm of material across all three passes (coarse, medium, fine). So:
- Light sanding (light wear, water-based finish): ~0.6 mm
- Standard sanding (medium wear, stain change): ~1.0 mm
- Aggressive sanding (deep gouges, pet stains, removing dark stain): ~1.5 mm
That gives a typical solid floor 4 standard sandings or 6 light ones before the wear is too close to the tongue to sand again safely.
How to measure remaining thickness without lifting a board
Same trick as engineered: pull a heating grate or look at a stair nose. Measure from the top of the plank to the top of the tongue (visible from the side). If the gap is:
- 5–6 mm — full thickness, like-new condition. Plenty of sandings left.
- 3–5 mm — sanded once or twice. Still safe for a standard sanding.
- 2–3 mm — sanded multiple times. One careful light sanding remaining, then screen-and-recoat only.
- Under 2 mm — the floor is at end-of-life as a sandable surface. Screen-and-recoat indefinitely, or replace.
The mistakes that burn extra thickness
- Skipping the coarse pass. Going straight to medium grit forces the drum to take more passes to flatten the floor, removing more total thickness than starting with coarse.
- Sanding across the grain. Cross-grain sanding tears wood fibres and requires a deeper subsequent pass to clean up. Always sand along the grain.
- Dwelling. Letting the drum sit in one spot, even for half a second, dishes the wood. The next operator has to sand the whole floor down to that dish — wasted thickness.
- Wrong grit progression. 36 → 60 → 100 is right for most floors. Jumping from 36 to 100 leaves scratches the finish won't hide and triggers a re-sand at finer grit, burning thickness.
What screen-and-recoat does for tired floors
When a floor is too thin to sand again, the alternative is screen-and-recoat: a fine sanding screen on a buffer removes only the existing finish (a few microns), the wood is wiped clean, and one or two fresh coats of polyurethane go down. It refreshes scratched-up finish without touching the wood. A screen-and-recoat can be repeated essentially forever as long as the wood itself is sound.
Cost is a fraction of a full sanding — we quote it during the on-site visit.