We have some cedar furniture in need of repair. Don't know the technical
term, but it's like tongue & groove. The seat slats are the tongue, and go
into a groove of a board, which the board is then fastened to the legs.
These were always loose, I'm guessing so they can expand/contract.

Wondering if I could kind of screw some new "slats" or boards across the
top?

Came home from vacation, and was missing our entire patio furniture. Called
the police, and while an officer was here, a neighbor a couple houses down
came by to see what the commotion was about. Come to find out, he
"borrowed" our patio furniture while we were gone for his daughter's
graduation party. They totally destroyed one of the lounge chairs, broke my
grill, and these chairs need repaired. Really don't know these people, but
he said he would purchase any lumber to fix them.

Thanks.