MDF use old or buy new.

[mimic]

I have few sheets of 3/4 MDF in storage unfortunately it's been there for few years now and it's a storage without A/C in Florida where it's pretty humid. Do you guys think this is still usable for a project or do I have to buy new one? What would be the signs of not being usable any longer?

[RetroArcadePro]

check if there is any swelling

[mimic]

Like when drops of water hit it and right away rises into bumps? Something similar to in the photo?

And if not then what? Good to go?

[RetroArcadePro]

I would check the thickness to check for swelling. Check if it easily bends/breaks. Cut a small part and see if it cuts normally.

I doubt the humidity did much to it other than maybe warp it some.

[Jamesbeat]

Also, check what position the board was stored in.
MDF has a nasty habit of warping when stored leaning up against a wall or similar.

It is called 'creep', and is one of the many reasons why I chose to use plywood instead of MDF for my build.