I think the main thing with ties is the interfacing, etc. could shift or shrink if washed. I speak somewhat from experience as I washed one of DH's ties once when we were traveling and he got a bad stain. It was completely wonky and ruined after that. The tie material (a synthetic, not silk) was OK but the interfacing and lining skewed. If I were making a tie quilt I'd prewash all the ties before disassembling. I'd guess that more ties are synthetic these days than silk.