Greetings,
OK...Bear with me, here.... I'll explain this as *I* understand it..

A Scottish kilt has no hem (of course) and the selvedge of the fabric *is* the "bottom edge".

Some Welsh mills (the one I bought *my* tartan from included) do NOT put such a selvedge on their fabric...Therefore requiring a hem, of sorts.

Perhaps a kiltmaker, experienced in dealing with such fabrics, could assist you? On inspection, my kilt has (sort of) a hem, and I'm quite pleased with the hang, and swing...

Just a thought!

Hal