The following are concrete and natural earth-based wall build systems that do not offgas toxins and are suitable for the chemically sensitive.
These are alternative build types, the options for building a healthy home apart from the standard timber frame, fiberglass, and gypsum boards.
Drywall now has its own dedicated post here: Guide to Non-Toxic Drywall Types and Brands.
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A mix of pumice and concrete is 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 odors that it may have picked up prior to installation.
Check out Margaret’s blog where she outlines the build of her healthy pumicecrete house.
An interesting material making a comeback, HempCrete is made of hemp and a lime-based binder. Hempcrete is either used to replace insulation in the walls or as the final wall itself.
They are not load-bearing so they are made with a wood frame.
HempCrete claims to not mold, but a natural fiber in a breathable wall is not something I would consider mold proof.
See my detailed post on HempCrete for much more info.
Consult with an architect to make sure this is right for your climate.
Wood Insulated Concrete Forms
Forms are made of a mix of remineralized wood and concrete. Inside, rebar is used as reinforcement and then they are filled with concrete.
Faswall is currently the only brand available in the US (2017). Nexum is available is based in Canada and they sell and ship across North America as well as to Australia and other Pacific Rim countries.
Aerated Autoclaved Concrete (AAC)
Concrete-based blocks made from quartz, lime or cement, and aluminum powder. Test thin-set mortar for sensitivity. Hebel is one brand in the US. It’s not approved in California (2017).
Insulated Concrete Form ICF
Nudura blocks (US and Canada) and Fox Block (US and Canada) are the most popular brands right now. ICF could mean different types of foam with concrete fill, but typically it is EPS. See my post on Insulation for a detailed review of EPS. Nadura has a dye. Both have flame retardants.
|Is Concrete Non-Toxic?|
Portland Cement is non-toxic. It should be confirmed that it is free of admixtures such as air entrainment and water-reducing agents, accelerants and retardants, and superplasticizers.
Ceramic Cement (Magnesium Cement) is also generally a non-toxic option.
Which Concrete Aggregates are Chemical-Free?
Natural non-toxic mineral aggregates should be used. Toxic aggregates include crushed brick, crushed sandstone, concrete slag, fly ash, cinder, and volcanic materials other than pumice. (Source: Prescriptions for a Healthy House).
Earthern Walls – Cob, Adobe, Light Stray Clay, Straw Bale, and Rammed Earth
These are all different types of walls made of clay, straw, and sand.
Houses made of all-natural materials feel great to be in and there is no need to worry about any offgassing.
However, there are precautions that should be taken to avoid mold. These types of buildings might be best suited to dry climates so that there is no chance of mold forming. Some people seem to be doing very well in adobe houses in the south-western US.
If straw is used in the walls it should be carefully sourced to be free of mold 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 are also very important to keep the walls from getting damp.
I’m hearing some bad stories of mold forming on cob and straw bale homes in cold climates, this is likely due to high humidity inside in the winter. I do not feel confident enough in this building system to recommend it for climates where it is not a native building practice.
Another natural wall system worth mentioning in a little more detail, Rammed Earth, uses sand, gravel and clay and has had an interesting development recently. Foam has been added for insulation and steel for support, and 5-10% cement is added to the clay mixture. It’s called Stabilized Insulated Rammed Earth.
Water does not penetrate the walls, however concrete, especially when not climate controlled is extremely prone to mustiness.
Corinne Segura is a Building Biologist Practitioner with 7 years of experience helping others create healthy homes.
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