为什么shower防水层（如hot mop）之前要做Pre Slope？网上的理由好像不make sense。真正理由是什么？

网上的理由是“Without it, any moisture that works its way to the Hot Mop would have no where to go. Over time the moisture would build up bacteria and MOLD, that eventually come up through the grout joints.”但是moisture到了斜的Hot Mop还是和水平的Hot Mop一样还是要停留那里，只是斜的Hot Mop会帮助moisture往低处（drain area）聚集。

写了上面一些时间后真正理由找到了，drain上有weep holes排水. 但是这个帮助有限，真正要做的是防止水到达防水层。