We are having to tear out bathrooms, because even here in dry Colorado, they are full of mold. The reason? Amateur builders who didn't know what they were doing. Water flowing into the wrong places, no vent fans, insufficient shower surrounds, misuse of drywall, leaking plumbing against drywall, impervious paint against unsealed concrete/ plaster walls, etc, etc, etc.

We will basically be rebuilding them from scratch.

Any ideas about materials, methods, etc to defy damp and mold will be appreciated. We are thinking of using a lot of lime plaster for walls, and sealed concrete for floors (we are in a basement.)

Edited to add; we would also like to keep things at least LOOKING rather standard, in case we have to sell.

Also, we hope to at least partially eliminate wall cavities.

Maybe you should explain what you mean by removing wall cavities?

-Generally for walls you want a concrete board surrounding the tub/shower area this will resist the mold when damp.
-ensure that all your stuff is not level, in other words you don't want your surfaces to drain in any direction other then the actual drain.
-Use quality shower/tub products that won't leak

Those are the basics, maybe you can give some more information for better answers.

Meaning, when we rebuild, not creating hollow walls which water can get trapped inside. Would this be possible with lathe and plaster between shallow framing members?

Of course, around any tub or shower we would use cement board or fiberglass. This would be for the other walls.

Hmm you want the walls not to be so packed with material that they hold water. Thinner could be ok.

You have to assume that bathrooms will always have a higher amount of humidity though so concrete is preferred over fibreglass to me and ventilation is really key.

I would build a Permaculture bathroom from scratch with a greenhouse clear roof for the sun to come in daily to sterilize. So bath/shower/basin and finishes must be able to handle this. Canvas screening just below can be used at times or even the roof itself can be able to open and close....Look here for ideas... http://www.vivasunscreens.com/external-sunscreen-systems

If the roof does not open then ventilation should be excellent to keep temperatures and humidity within range - like a wall extractor fan run off solar... and/or 'whirly bird' in a corner drawing out heat [turbine ventilator]. There are DIY extractor fan examples on YouTube or Instructables that I have seen somewhere that have been put into windows and looked good.

Resale - just explain how hygienic the bathroom is and reasons for special design. Will be seen as a real plus by the right buyer.... especially if mould is a real problem in the area. Sunlit areas defy mould growing. Also great plants can be grown in pots away from walls and could make the bathroom look amazing.

As a side-note: Is excellent for chicken houses too. I am building my chicken house in my whole mandala system with most [not nest-box area] of the roof clear for this reason... sterilization via sun in the day on the bare earth deep litter system. Main outside run will have cool areas for the chickens to rest in when hot.... as will mandala of grow-beds around the main barn and run.

Mold on or in building surfaces is a function of temperature and humidity. Low temperature surfaces + high humidity = condensation. Of the many comments here, I think Sean's ventilation suggestion is the best. Install a stronger vent fan and duct it properly to the outdoors. Avoid bends and keep duct runs short. Install a high quality wall cap that will not backdraft cold air. Many newer, high quality vent fans have ports for 6" duct which might be necessary. You want a measured 50 CFM being exhausted as a minimum. Installing a much higher CFM fan is sometimes necessary to get this smaller, actual measurement due to poor duct layout and design.

Several of the other comments could make the problem worse. You want to increase the temperature of the bathroom surfaces. Skylights and removing insulation will not help this variable.

If you are tearing out walls anyway, use mold resistant drywall (at least) for the entire bathroom. If you can afford it, fiberglass backed drywall or cement board would be better but probably not necessary if the exterior walls are air sealed, insulated and you use the vent fan appropriately. You might want to consider wiring the fan and light together on a timer to ensure its proper use.

Hi Gilbert,

Of all the advice given, (and this being a traditional-natural building forum) I would say the main thing you need is good ventilation. There are several ways to do that, but without wall interstitial schematics and other knowledge about the building and your skill sets I can't really go farther. Ventilation is number one.

Chelle's advice is spot on and I have build several like that. If you have a masonry wall and the skill sets to embrace the work required, greenhouse, solarium or vivarium bathrooms are the very best. Some I know of become the favorite place in the house. Plants, moving water and air can really inhibit "bad molds" and promote a more natural system. Anyone that has spent time inside a nice green house knows just how pleasant they are.

Personally I would stay as far away from many of the mainstream commercial building products like wall board, cement board, and the like. I would support the use of NHL5, cob, natural cements, stone, tile, and several forms of AAZPA approved epoxies to make certain things if the design required it.

Regards,

j

Use magnesium oxychloride panels instead of Sheetrock. MgO dries things out and mould will not grow on it. Then fill the wall cavities with a magnesium oxychloride foam. We used magnesium chloride for our salt but the airkrete guys use calcium chloride. Either form of foam will inhibit mould growth and neither are poisonous. The old hospital surgery rooms had terrazzo floor because the magnesium would desiccate pathogens and keep it sterile.

Good luck,

Jason

Will the lime plaster or a lime whitewash inhibit mold growth?

Hey Gilbert,

I completely concur that ventilation is the key here. Do you intend to fix this yourselves, or hire a builder? Since you are correcting amateur building mistakes, be careful to avoid making new ones if you are doing this yourself. If hiring this out, not that many builders will understand the Permaculture view of the world, and think outside their conventional building box and consider alternative materials and methods.

Jay's comment is right on: no one can give you a definitive answer without knowing more about the construction details. If you root around enough to make accurate drawings of how the walls and ceiling are constructed (I'd aim for cross-sections that show any nooks and/or crannies), you may need to hire a consultant or get added comments here to make sure the cure is better than the disease.

One word of caution: There are plenty of examples out there of "greenhouses gone bad"! A greenhouse, trombe wall, or other passive solar element still has to be thought through, and adequate air circulation and moisture management is extremely important. A greenhouse or solarium can add a lot of heat and light to a building, but usually a LOT of moisture, as well.

On the equipment side, if you are on-grid, Panasonic makes pretty nice small bathroom vent fans, and even some with heat recovery built-in. For smaller, tighter homes, these could even replace a heat recovery ventilator. In some cases you really want an ERV, not an HRV, so again, consulting someone like Jay that does this professionally will be very beneficial.

I have heard that natural plasters with finely ground bio-char help inhibit the growth of mould and fungi. worth looking into for a carbon sequestering, mould inhibiting, low cost, biodegradable option.

We will be rebuilding by ourselves, and we don't want to take on the risky project (for amateurs) of building a greenhouse, solarium, etc. So it will have to be fairly standard. But we hope to do better than the last folks. For one thing, we will not attach tile to drywall and expect it to stay dry!

Thanks for all the advice on here. We will probably be incorporating some of it in our project, once we are done ripping everything out.

Build an outdoor restroom!
Of course I suppose this depends on the region you're in. I'm in South Texas, works just splendid for me.
But yes, I agree, ventilation should be the priority (that's why I just build mine outside, with three walls and vents just below the eves.
Perhaps lime plaster walls would suffice?

Jay C. White Cloud wrote:Hi Gilbert,

Of all the advice given, (and this being a traditional-natural building forum) I would say the main thing you need is good ventilation. There are several ways to do that, but without wall interstitial schematics and other knowledge about the building and your skill sets I can't really go farther. Ventilation is number one.

Chelle's advice is spot on and I have build several like that. If you have a masonry wall and the skill sets to embrace the work required, greenhouse, solarium or vivarium bathrooms are the very best. Some I know of become the favorite place in the house. Plants, moving water and air can really inhibit "bad molds" and promote a more natural system. Anyone that has spent time inside a nice green house knows just how pleasant they are.

Personally I would stay as far away from many of the mainstream commercial building products like wall board, cement board, and the like. I would support the use of NHL5, cob, natural cements, stone, tile, and several forms of AAZPA approved epoxies to make certain things if the design required it.

Regards,

j

I agree with the use of NHL(Naturally Hydraulic Lime).

Tadelakt is also something worth looking into, its a Moroccan practice of limework used in their bath-houses.

http://www.stuccoitalianoinc.com/application-instructions/how-to-tadelakt/
http://ecobrooklyn.com/tadelakt-moroccan-plaster-technique/