Polly Esther wrote:

If I were going to make a t-shirt quilt (and I are not), I would first iron
on a block of lightweight interfacing behind the area on each tee that I
wanted to use for the quilt. Even before I cut the shirt. Those t-shirts can
stretch, warp and curl before you can blink. There are interfacings that are
soft and won't make your quilt stiff but that would give you some control.
Polly

Yes, definitely interface.

I made a tshirt quilt without it... It's a good thing the recipient
wanted high-loft and *tied*. That way it doesn't matter how loose the
shirts move. I didn't even sash the shirts. I do not recommend that
method to anyone.

-georg