In article , Newshound
writes
Next time you are putting hardboard on a wooden floor get one of the
cheap-ish electric nailers from Screwfix and use lots of 15 mm pins.

I did mine rough side up, edges butted tight together, nailed at 9" centres
all round the edge, an inch in & with the middle nailed at 9" centres too. I
taped the seams with duct tape which should not show through.

Oh, and buy your hardboard from a builders' merchant, not that gloss faced
cardboard you get in the sheds that wont hold a nail.
--
fred