Hardwood floor cupping or warping
moderate 1–3 h
Tools: moisture meter (pin type), flashlight, hygrometer, dehumidifier and fans, straightedge · Materials: a vapour barrier for a crawl space, dishwasher or fridge supply line if either is weeping
Steps
- Look for the moisture first: cupped boards near the dishwasher, fridge, a bathroom door or an exterior wall point at a leak; cupping across the whole floor points at humidity from below or in the room.
- Measure the boards with a moisture meter on top and, if you can, from below — wood over about 12 % is wet, and a big difference between the top and bottom readings confirms moisture from underneath.
- Check the crawl space or basement for damp soil, a missing vapour barrier or a leaking pipe; check appliance supply lines and the base of the toilet and tub.
- Fix the source, then dry the floor slowly with a dehumidifier and fans for several weeks — measure until the readings stop dropping.
- Do not sand a cupped floor until it has dried and flattened; sanding it wet leaves it crowned when it dries.
- If mild cupping remains after a month of stable readings, accept it or plan a screen-and-recoat; deep cupping needs sanding and refinishing.
Stop and call a pro if
- the floor is spongy, boards are buckling upward, or there is a water stain on the ceiling below
- the moisture readings keep rising with no visible source — a slab or a pipe under the floor is leaking
- the cupping covers a whole room over concrete with no vapour barrier
What a pro does that you can't
A plumber finds the hidden leak, a crawl-space contractor installs a vapour barrier, and a flooring contractor sands and refinishes once the wood has stabilised at the right moisture level.
DIY cost: $20–40 for a moisture meter; $150–300 for a dehumidifier