A mix of pumice and concrete are poured into forms to create these non-toxic walls. They can be made load bearing with a concrete beam. Test pumice for radioactivity and for odours that it may have picked up prior to installation.
An interesting material making a comeback, Hemp Crete is blocks made of hemp and a lime based binder. The blocks are used to form the walls and act as insulation. They are not load bearing so are used with a timber frame.
Forms are made of a mix of remineralised wood and concrete. Inside, rebar is used as reinforcement and then they are filled with concrete. Insulative fibers can be added or they can be filled with part concrete and part clay or a non-toxic insulation. Brands include Durisol and Faswall.
Concrete based blocks made from quartz, lime or cement, and aluminum powder. Test thinset mortar for sensitivity.
Wall Boards: 0-VOC Drywall
Magnesium Oxide Board claims to be VOC-free. They are a cement board that is more prone to cracking than regular drywall. People have run personal tests and found some of it to offas so I would test this against personal sensitivities. I would use an American brand to be on the safer side.
National Gypsum makes natural gypsum boards that are VOC-free (the paper backed ones). It's not always easy to source and I would rather not have paper-backed dywall.
For easy to source wallboards that are GreenGuard Gold certified, try DensArmor plus, and Georgia-Pacific Gypsum board are all GreenGuard Gold Certified (Densshield tile backer not Greenguard gold). Certainteed Gypsum boards and USG Sheetrock claim no VOCs.
AirRenew which is also GreenGuard Gold, claims to soak up formaldehyde. However, it contains a biocide which is likely not healthy. It is a little harder to source than the ones above.
In wet areas such as behind showers, tub, and sink, cementitious boards should be used. MgO board, Durock (0-VOC), Hardibacker (Greenguard Gold), or Permabase.
Natural Building: Earth Based Walls
Cob, Adobe, Light Clay-Straw, and Straw Bale and Rammed Earth
|Adobe house from trails.com|
If straw is used in the walls it should be carefully sourced to be free of mould and pesticides. When building with cob, adobe or light clay straw there needs to be a dependable dry season of three months for the walls to dry out properly. They are particularly suited to be heated with wood stoves as that dries out the walls well in the rainy and damp seasons (source: Econest). An above grade stem wall and proper drainage around the house is also very important to keep the walls from getting damp.
I'm hearing some bad stories of mould forming on cob and straw bale homes in cold climates.
|Rammed Earth from sirewall.com|
Water does not penetrate the walls.
Paula Baker-Laport has more tips for mould free construction of earth based walls in her book Prescriptions for a Healthy House: A Practical Guide for Architects, Builders & Homeowners