Julia Diamond wrote: My question is, what are good natural alternatives to sheet rock, backerboard, tape and mud.
Wow, that's a tough one. One alternative is a tough, rigid styrofoam, maybe the 2"-4" thick stuff that is used to insulate concrete pours, but it's certainly not a natural alternative. Tile goes down pretty well onto a plywood backer, but then again, plywood is not something I think of as "natural". Since you want to get it done soon, I think you are going to have to settle for expedient at the cost of being natural.
Do you have good insulation behind your lath?
You know tiling your outside walls is going to make those walls freezing to the touch even with good insulation in your walls just saying, tile is a cold winter companion.
A good site for this is - http://www.mychemicalfreehouse.net/2013/02/a-non-toxic-bathroom.html
MgO board is a cementitious wall board ideal for those with chemical sensitivities.
It is non-toxic, VOC-free, and a very impervious to mold. If you have a wood-framed
wall it will be easy to attach the board to that. Good brands are Dragonboard, Mag Board and Magnum Board
You can plaster, paint or tile over MgO walls. Here are some tips on using plaster.
If not painting, the MgO boards would need to be primed.
From what I gather the dormer is above the bathroom on the second floor. How tall are the exterior walls you are placing the tub next to? Inches to the roof? Is this an attic remodel? The dormer has fixed glass or what type of window? Is there a bathroom fan? If not install a well insulated one w/a flapper for the size of the room and use it.
Lime would not be an issue here since other than having to keep it wet a couple times a day 2-4 weeks, and in a functioning bathroom that is easy. It is labor intensive but since you already have the lath an option. Lath is not cheap. If you are not familiar with lime get on the American Lime Associations website and read their publications. It is an acquired skill not a quick DIY.
Your roof is 2 x 6 lumber, the cavity should measure 5 1/2 ". You could use denim insulation it dries fast, has borax or boric acid as an anti fungi and fire retardant. I'd recommend mineral wool in a bathroom. It will provide R-21, in Detroit roofs s/b R-38+. If you have the head height add Roxuls (1-2)stagger 1.5" boards for another 3" R-6-12 to the ceiling I'm guessing is cathedral/vaulted? There is no flashing req'd on the underside of roof sheathing other than if you install a fan follow the mfg and silicone caulk any existing fan.
Walls should be insulated to code min there is R-20, if not Jami is correct they will thermally bridge into bath tiles, use fiberglass surround unit if you can. Tiles use a hardiboard cement board rather than Georgia Pacific's backer board with acrylics. You can also use the plastic you take off the walls to thermally break the wall studs and/or add some Roxul IS boards.
I recommend removing the vinyl tiles over plaster. For quick, known, DIY, etc.... and easily accessible I'd use a fiberglass faced and taped gypsum board like GP DenseArmorPlus: http://www.buildgp.com/densarmorplus-high-performance-gypsum-panels No microbial producing paper, FG just like mag board. I'd steer clear of DragonBoard or any Magboard from China too many quality control issues and little tech data to prove it's sustainability especially in wet environments. Foreverboard here in NY is an option and the only US mfg if you fully understand mag board and the industry. Not DIY friendly. Better to go with a higher grade gypsum w/FG like GPs, etc. Due to expansion and contraction use it everywhere, all walls. It has a perm rating greater than 10, can provide some humidity buffering up to 5% it's weight....not as great as lime or clay but not bad. To get more add a mud hot coat using 1:1:2 (mud: type s lime: sand (80 grit jagged edge mason: mud: (Wespac, Murphy). Use a high perm siloxane sealer, lime wash or mineral silicate paint like ROMA or Heim.
I've been to this facility in Chicago before they are doing some interesting things with hemp/lime not far from you: http://www.americanlimetechnology.com/
Somebody else mentioned no tile next to exterior wall so I will skip the tile on that wall and stucco with a lime wash.
Depending on the type of “stucco” or a better term for interior walls “plaster” and its cement percentage, it can thermally conduct or “bridge” across a material as much as tile. I suggested using fiberglass bathtub surround unit if you have the head height since it does not conduct heat as much. I also suggested taking the plastic off the other walls and using it on the studs and between a plaster lath or tile backer boards since plastic is not very thermally conductive to create a ‘thermal break” if you will between outdoor air and the inside of the bathroom. The same would apply behind any tub or combo units, install the backer or gympsum boards and plastic thermal breaks to the studs. Another thermal break I suggested is Roxul Comfortboard IS rigid insulation boards, in addition to above can really insulate this bathroom well but it will not be cheap. Sounds like your biggest problem as far as insulation will be the dormer glass so it may not be worth spending a lot of money on the wall and roof insulation.
I have a question. I converted a garage into a guesthouse in los Angeles. For the bathroom walls including surrounding the tub, we just "stuccoed" over the drywall--just like you would with exterior stucco-flashing, chicken wire and then three coats (brown, scratch and top coat) and then I painted with old fashioned oil based enamel paint on that--12 years later its still beautiful and impermeable
It is hard to compare a bathroom in LA to Detroit without knowing all the details. I can tell you just because things look good on the surface does not mean they are good under the hood. If you want a breathable wall “impermeable” is the wrong word, as is using oils on interior plasters, that can create vapor barriers and reduce drying.
Commercial stuccos are good for exterior wall applications since they contain high levels of Portland and other cements that make them super strong but impermeable. The higher strengths are also driven by code to meet structural requirements for bracing walls.
Interior plasters do not need so much cement or density to hold up to the elements, nor meet as high structural requirements, often none. They are therefore more “permeable” for breathable walls.
There are a lot of contributing variables to both but that is the basics.
I think you’d have a good plan to install the DenseArmorBoard w/a hot mud coat and lime wash everywhere, sealed with a siloxane sealer you can get local concrete supplier until water beads up on the surfaces. Take care of the roof and exterior walls insulation as described. You can then tile the tub surround if you want, or, go with a permeable interior plaster like lime or American Clay has some good high perm products but more expensive than the DIY hot mud coat.