"krw" wrote:

What type of joint would you use for
edging? BTW, the edge board I'm doing is about 4" wide; a little
less
after I rip everything down to final size.


Given a choice, I'd use tongue and groove.

Tongue in the wood, groove in the plywood, forget the biscuits except
at the corner miters in the wood.

YMMV

Lew