On Monday, May 8, 2017 at 1:55:08 AM UTC-4, wrote:
On Sun, 7 May 2017 20:34:35 -0400, Frank "frank wrote:

On 5/7/2017 7:46 PM, wrote:
On Sun, 7 May 2017 16:09:07 -0700 (PDT), Andy
wrote:

I have a 2 x 4' piece of underlayment lumber.

Any way to flatten it ?

Thanks,
Andy
Nail it down.

The real answer is probably put it in a container large enough to pump
steam around it for a couple of hours, take it out and bend the hot
board and clamp to let it dry and set. Seen it done for making
furniture but who in their right mind does it for a 2X4? Easier to buy
a straight piece.
2 foot by 4 foot (8 sq ft) of plywood, not a 2X4

Assumed plywood. Probably right, but definitely assumed.