-never get mouldy
-last a lifetime
-and hold up in a tiny mobile home (that flexes when it moves)!
But we did it! We were this close to giving up and building an outdoor shower. In the end, the shower enclosure was made of aluminum and stainless steel with a zero VOC adhesive.
The details are below, but first, some plans that didn't work (but may work in a non-mobile home).
What didn't work for me:
My first plan was tiles, but grout without additives (plain Portland Cement) may not hold up in the long-run to mould or to cracks in a mobile house. Even with Schulter barrier underneath, I still wasn't confident the area around the drain would hold up to cracks when the house moved. I also could not find a zero-VOC grout sealer to totally waterproof it.
A non-toxic waterproof finish, tadelakt was also considered. However, all the plaster in my house has cracked. Some ideas to give it a little flex include - adding glue to the plaster and maybe a mesh underneath on the wall, but no one has tried this yet in a mobile home so it is a big risk and I don't think it's a good idea. In a regular house (not on a trailer) this would be a good choice for many. Though it requires a lot of upkeep. (For the base/floor you still need tiles, fiberglass or metal).
Fiberglass or Acrylic
Will last a lifetime without getting mouldy but if you get a company to install it they need to use their own adhesive, which is hugely toxic. Fiberglass offgasses and most highly sensitive people say they react to it. If you found a used one or let one offgas and then installed it yourself with your own non-toxic adhesive this could work. Acrylic may be more tolerable. If you use one of these showers you have to design the size of the bathroom around that (we didn't).
In a regular house, polished concrete might work really well, if you can find someone who can do that finish on walls and tight spaces. Glass walls are something to consider. An outdoor shower could be made of cedar, glass or concrete. More discussion on these materials in my post on bathrooms.
My Chemical-Free, Mould-Free Shower!
A basin with 2-inch sides is made of stainless steel and the pipe in the center is welded in so will never leak around the drain (Stainless is going to hold up better than alum in the basin).
I would have done more of a grade and a higher lip on the basin if I did it again. Underneath we used pieces of acrylic and Butyl Sealant Tape to support the grade.
The second piece of aluminum overlaps over the first piece and goes up to the ceiling. A vent is right in the middle of the shower on the ceiling to reduce moisture. I am wondering if I should have had a piece of aluminum made for the ceiling as well.
this EVA non-toxic one (had a slight plastic smell but was fine for me) (other curtain options to try are polyester or polyethylene - or, even better make a glass door). My curtain has magnetic pieces that stick to the walls - to prevent water from splashing out onto the tiles which are not 100% waterproof (magnetic strips from Bed Bath.......and Beyond!)
After testing many adhesives with no luck I finally found Almighty Adhesive by AFM and had no reaction at all to it even when wet! The problem of finding an adhesive was holding up the project for months and I was so excited to finally find this. It is also the only adhesive (including silicones) I have ever smelled that really is non-toxic. Even a regular non-toxic white glue smells more than this stuff.
Around the edge of the aluminum will be sealed with AFM caulk which does take about a week to offgas. I really want all the edges to be sealed. Strangely (happily) I no longer find this caulking to be problematic but I think Ecobond is less toxic.
So there you have it! A shower that will never leak or become mouldy and with no toxins!
Once thing I would have done differently is not use any batting insulation in the bathroom walls. If moisture gets into the walls then it's over in terms of mould. I would have used only hard foam.
Another thing to consider is to weld all the parts together. See Tiny Green Cabins stainless steel showers if you are interested in that route.
The custom aluminum and stainless cost 800 CAD + installation which took 2 people all day. (We had to re-do some plumbing though which took longer than expected)