For under floor boards I would using a system like this (link).

His shoes and legs felt wet, he looked down to see water rising from the floor boards.

In half a dozen minutes, he had enough floor boards ripped away.

The object is to sand with, not across, the grain of the floor boards.

Another creak from the floor board at Janice's next step.

A sharp metal point was sticking out of the floor boards.

I came in to see what he was doing and found him working on the floor boards.

They took another step and a floor board smacked them in the nose.

On March 23, 2013, the floor boards of the waiting room were completely replaced.

The police also found $70,000 in $1 bills stashed under floor boards, he said.