Two questions similar subject --

trying to avoid mold issues (had bad past experience) in new construction.  But we're on major tight budget now.

1) Love the Schluter Kerdi shower system but it would cost almost $1000 more than regular ol' shower pan liner/mud made by tile guy.  Is the Schluter worth it?  We have two showers.  One will get lots of use.

2) We wanted river rock (either flat or whole rocks) in shower floor but worried that is asking for a mold problem down the road.  We're using unmodified non-latex unsanded (no polymer/no chems/no antimicrobials) grout and thinset b/c of chemical sensitivities. 

3) Also wondering if slate tile shower floor is a bad idea - same reason

4) Is there a good green/nontoxic slate/natural rock sealer for showers?

Been off line for a while.  Catching up.  Regarding Kerdi, I recently used it for a new shower I installed.  Our dimensions didn't fit a standard size so we did a mud pan and used the Kerdi drain and standard Kerdi membrane with their corners as well as Kerdi on the walls. Worked nicely and less difficult than running lead or PVC membrane.  It was nice however for the curbing. Simple install. For a DIY'er, I'd highly recommend it.  For a pro?  standard systems have worked for a long time.

I'm going to guess that if you cover rocks or slate with clear epoxy, they will dry quickly. I have a wood (ipe) grate in a shower with no coating and it is fine.