We built a tiled shower using tyvek instead of roofing felt behind the substrate. Is that OK? The tyvek was stapled directly to the studs and overlapped the shower basin lip. 1/4 " hardybacker was next installed and all seams were taped and mortared. The tile was bonding mortared to the hardybacker and grouted. There was a shower seat that was sloped and tiled also. In the seat area the tyvek was not cut but folded into place. Can tyvek be used in place of felt?