plaster shower walls, how to do them today?

Question

I have an American 1950's home. It appears the previous owner covered original plaster walls with an inexpensive glue together shower panel system. Most of the homes in the area were built with tile bathtub/shower walls, but mine seems to have never been tile. I am considering removing all the original plaster down to the studs, then recovering with cement board and plaster.

I looked around here, the best post I find is How to better waterproof the shower area? which points out it does not matter much what you cover the wall with it is what is behind that matters. I searched google a bit and found several walls that seemed to be plaster.

Random example

What is the recommended approach for plastering walls in a shower? Are there any specific products or practices that I should or should NOT use?

Answer 1

What you cover the walls with certainly does matter if it can be damaged by water, as many forms of plaster can--such as modern gypsum plaster, which softens and disintegrates in the presence of water. The only way I can imagine a plaster shower working is if you perfectly waterproof the cementboard with a paintable waterproofing membrane like RedGard (preferred) or poly sheeting behind the cementoard, and then use old-fashioned lime plaster, and then paint the lime plaster with multiple coats of a waterproof but vapor-permeable silicate mineral paint or some other type of vapor-permeable waterproofing agent.

But this is a totally non-expert perspective; I have never built a plaster shower and the whole idea sounds risky and ill-advised to me. If you want to go with this approach, you should probably bring in a pro.

Answer 2

It's not clear to me what form your new shower will take, whether it will be a commercial modular system ("glue together shower panel system") or if you want to build a new shower yourself. I've recently stripped my shower back to the studs and built a tiled shower. I got a lot of great direction from the Floor Elf. Don't let the name (or the dry, self-deprecating humour) fool you --- this guy knows his stuff, and he's shared a lot of his knowledge on his site. You can piece together how to build a tile shower from his various blog posts, or you can buy a "Complete Shower Waterproofing Manual" (customised for the various designs) for a modest fee of $20.

Regardless of how you're going to build your shower, you have to be aware that plaster is not waterproof. If the walls in question are going to be exposed to water, you should not be using plaster. Walls near but not in a shower should be greenboard (regular drywall with a water resistant facing). Walls in the shower should be waterproofed with one of a variety of methods:

• Traditional waterproofing (plastic sheet) behind cementboard
• Topical liquid membrane (e.g., Redgard) over cementboard
• Topical sheet membrane (e.g., Kerdi) over greenboard
• Commercial modular system

Answer 3

What you want to do is certainly possible. I'm planning on doing a similar thing. Waterproofing is the key. You want your wet walls to be able to dry to the outside of the wall and not retain water or let water travel inside the walls where it can possibly grow mold.

There's a special product I've looked into that's not available in my area called super shower finish, from Merlex. I'm currently figuring out how to do something similar to it but with products from home depot or Lowe's. Their process for doing it over cement board is to use a base layer of their Base X product (which is a polymer enriched mortar)over the cement board, and embed a 4oz fiberglass mesh into it to lessen cracking. Then put the super shower finish over that surface.

My thought is to use a paint on waterproofer (like red guard and others) over concrete board, a polymer enriched thinset for the base layer, with the mesh, paint on an acrylic binder after it cures (gives the final layer additional working time and adhesion), and finish it with either ardex feather finish, or a cement resurfacing product or something. I haven't used either of those products so I don't know how they'll work. Specifically, I don't know how the resurfacer goes onto vertical surfaces and I don't know how the feather finish handles water.

There are many companies that have "micro cement" mixes, but none of them seem to be in my area as far as I can tell. You might have better luck. Each of them might have their own ideas for how to build the wall to last in a wet area of the house.

Another solution would be something called Tadelakt. It's a lime plaster finish used in Moroccan bath houses for centuries. It's a bit labor intensive apparently and the waterproof layer is on the outside, which means if it gets damaged with harsh chemicals or rough treatment, the waterproofing is gone and the whole wall will have to be redone (according to what I've read). It's waterproofed with a "black soap", which is ash and olive oil, that creates the waterproof surface and binds with the lime more as time goes on.

Apparently, a well done Venetian finish plaster job can also create a waterproof wall, though I'm not sure a shower is the right place for it.