I have not been able to get 3/4" (19mm) welded stainless steel mesh either.  I have used woven mesh, and don't have problems.  I generally spec 3/4" or 1" mesh.  Got to keep those sparrows and starlings out.  Their shit might be smaller, but the nests are a real pain.

Don't compromise with him.  Get what you asked for.  Woven is not that much heavier than welded.  Consider a lighter gauge - you don't need much.

Bent or folded mesh can do good things ... but remember to get joints laced - I require stainless steel wire to lace the joints at corners and junctions of sheets.

Keep the birds on the wing.

david

PS  Any opportunity to use stretched fabric mesh (hail net or bird net)?  This can be very effective too.