What a cupped board is telling you
The underside of a floor is usually unfinished and takes up moisture faster than the sealed top. Those lower fibres swell, the board tries to grow wider on the bottom face, and the edges lift.
This is diagnostic rather than ambiguous. Cupping always points down at the source, and the source is a building problem rather than something the floor did wrong.
- How it is done
- cupping means the underside is wetter than the top
- What goes on the floor
- n/a
- Ready to use
- n/a
- Typical cost
- n/a
- Service life
- n/a
Finding the source in a Des Moines house
In Des Moines the four sources, in the order we find them, are an unsealed crawlspace with bare ground, a basement running above 60 percent humidity, a slow plumbing leak, and a gutter or grade discharging against the foundation.
It is confirmed with a meter: readings from the board face, from the underside where there is access, and from the subfloor. A higher number underneath is the diagnosis.
The order of work is fix the source, then dry slowly, then wait a season. A large share of cupping reverses on its own once the moisture stops, and the floor that flattens by itself needs no sanding at all.
Sanding a wet floor flat
Sanding a cupped floor flat while it is still wet is the single most expensive error in this trade. It looks perfect on the day. As the boards dry they shrink, and the floor ends up dished in the centre of every board, permanently, with less thickness left to fix it.
Where we work
We cover Des Moines, the western suburbs, the Ankeny corridor and the older neighbourhoods inside the city, including and 18 more areas.
Questions we get asked about why hardwood floors cup
Why is my hardwood floor cupped?
More moisture below the boards than above. Crawlspace, basement humidity, a leak, or water getting to the foundation.
Will it flatten on its own?
Often, once the source is fixed and it dries slowly. Give it a full season before deciding to sand.
Can you just sand it flat?
Not while it is wet. That guarantees a dished floor later. Dry it first, then see what is left.
Get a free estimate
Tell us what you need. We answer the same day, the free estimate is on site, and nobody chases you afterwards.
Get your floor looked at
Call and we will come out, measure, and leave you a written quote. There is no charge for the visit and no obligation afterwards.