I had six old oak floorboards to lay in my 500 year old house. My problem was that the floor was not flat but curved down 10 cm towards one corner
I tried
- Fixing one end of the floorboard in position and putting a heavy weight on the other end. Result - no noticeable deflection in five days
- As above but laying a wet towel on top of the floorboard where the bend needed to be. Result - no noticeable deflection in five days
- At which point I gave up pussyfooting around and enthusiastically used a wallpaper steamer where the bend needed to be. That was the magic ingredient which made the floorboard sufficiently flexible that I could stand on it to get screw and penny washer fixings in position. Result - one week later I loosened a floorboard and found that the board had deflected by a couple of centimetres.
I dont trust it to stay deflected so I fixed it back down with screw and penny washer. In a month or two I will remove the penny washers and countersink the screws
Anna