Updated October 2019
This post contains affiliate links to relevant products that I use and recommend. Upon purchase, I earn a small commission at no extra cost to you.
For individual help on choosing the best products and materials for you and your home, you can schedule a consultation with me here.
Non-Toxic Thin-Set Mortar
Thin-set is the layer that goes down under your tiles. Concrete based thin-sets are the safest and are also easy to source.
I used Custom Building Products Standard Thin-Set Mortar which is zero-VOC (and mildewcide-free). It had a bit of an odor when wet but seemed fine once dry. You want a basic concrete based thin-set that is not mixed with latex or acrylic additives (like this one).
The unmodified one is recommended for floors and may not be suitable for all applications. Schulter also makes SET, an unmodified thin-set mortar.
These non-toxic thin-sets are more prone to cracking than ones with more additives, and you have to check if your application requires polymers. Thin-set mortar is also known as dry set and dry bond.
Avoid the toxic epoxy thin sets. Avoid toxic mastics as well. Although there are some safe and tolerable tile glues like AFM 3 in 1.
Non-Toxic Tile Membranes / Underlayments
Over the first layer of thin-set, I used Schluter DITRA (polyethylene with a fleece backing), an uncoupling membrane that will help prevent cracking when my tiny house moves (it worked well and did not have an odor to me).
Polyethelene is a very safe plastic. In regular-sized houses, you can use this as well to prevent cracking.
If you just need a waterproofing membrane, use Schluter Kerdi (a modified polyethylene (PEVA) core with non-woven polypropylene).
For a tiled shower, the Kerdi shower system is recommended by architects to create a mold preventative shower.
Be sure to test all parts including Kerdi Fix sealant if you are sensitive to chemicals (though you can use your own thin-set, as long as it’s compatible).
Instead of using the membranes over backer boards (baker boards discussed in this post), you could use Kerdi boards or Wedi panels. Test for tolerability before proceeding, they are not odor-free.
These simplify things by replacing concrete backer boards + membrane with one layer that is easy to waterproof. The panels are non-toxic 0-VOC polystyrene with a membrane already integrated.
Concrete Based Non-Toxic Grout
Concrete grouts are the safest grouts and are generally non-toxic. You don’t need to go to a green building store here, their grouts can be found at regular building supply stores.
I used Custom Building Products Polyblend grout, the same brand as the thin-set, which is also 0-VOC and contains no mildewcides or antimicrobials.
It barely had an odor, though it does have polymers that may not be tolerable to some. Almost all do well with this.
If that one doesn’t work for you, Hydroment is also recommended for people with sensitivities. However, it has a small amount of latex additives and contains mildewcide.
If you need to avoid all additives, you can make your own with Portland Cement (no additives) mixed with sand, lime, and water for a totally chemical-free grout. Here are the ratios from Craftsman’s Construction Encyclopedia. To mix your own unmodified grout it is a ratio of Portland cement to sand, 1:1 for 1/8th joints, 1:2 for 1/2 inch joints, and 1:3 for over 1/2 inch joints. Adding up to 1/5 lime increases workability.
What are Grout Additives and are They Toxic?
Those who are sensitive will probably want a concrete-based grout (like those above) and then see which if any additives can be tolerated. Since additives are trade secrets and polymer is a word that can mean a variety of chemicals (there are over 10,000 polymers that can be used in cement) you will probably have to test them.
Common polymers in grout include: latex-based, Acrylate copolymers (acrylic eg. PVA), Styrene Butadiene Rubber copolymers (SBR), Vinyl Acetate-Ethylene copolymers (VAE), and Ethylene-vinyl acetate (EVA).
They might come mixed in or you might mix them in yourself. Mixing them in yourself has the advantage of being able to test the additive against your sensitivities in a more concentrated form, on the other hand, you may not want to test the polymers and the grout until it has cured.
Polymers are added to improve chemical resistance, reduce porosity, improve flexibility, and freeze/thaw stability (source).
You will have to find out when and where you need additives, which depends on your project.
Are Thin-Set and Grout Safe – Why do They Have the Prop 65 Warning?
Sanded grout and thin-sets contain silica (the same substance as glass) which is harmful to breathe in when in dust form; you will see a Prop 65 Warning on every product that contains silica dust.
Use an N95 mask (or better) when mixing it until it is fully wet. This is completely safe when it is no longer in dust form.
There may also be other minerals in there that are only a problem in dust form like aluminum oxide, which can result in a high health rating on the SDS and other warnings. Again, these are safe when it’s mixed wet and when it cures.
Some cement contains fly ash and others don’t. Otherwise, plain Portland Cement does not have any other harmful additives.
Non-Toxic Thick-Set /Thick-Bed Mortar
Thick-Bed mortar (also called thick-set or mud set) in it’s most basic form is simply Portland cement and sand. Custom Building Products makes a mix of 1:3 that is unmodified, it contains no chemical additives like polymers.
This is harder to source than thin-set.
Alternative to Concrete-Based Grout
For something more waterproof check put QuartzLock; this won’t be tolerable for everyone. It is a urethane-based grout, not cement, and provides more waterproofing.
This grout it significantly high in offgassing and I don’t know a good reason to use that over basic cement-based grouts. Your waterproofing needs to be done properly behind the tiles.
Non-Toxic Tile Types
I used concrete tiles from Morocco in the picture above. For more info on choosing non-toxic tile types, see my post on flooring.
Non-Toxic Grout Sealers
If just sealing grout (and not tiles) you can use AFM Grout Sealer (0-VOC, one of AFM’s most tolerate products), Custom Building Products grout sealer that many people do well with, less than 1 g/l VOCs. ECOS, a well-liked brand has a stone sealer that can be used on grout.
If you don’t do well with any of those, you can check out more concrete sealers (which can work on grout) in the last section in the post on sealers.
Sodium silicate (aka water glass) is an idea that gets mentioned a lot among the chemically sensitive. When I spoke with a company that makes sodium silicate they recommended against using this on tiles in the shower. This brand Conkrete-Seal has been used by someone very sensitive, she said it was somewhat waterproof and she was happy with it in the shower. Technically it’s a densifier and not a sealer, and normally it doesn’t claim to make concrete waterproof. It is used in concrete polishing systems like Retroplate and as radon sealers in concrete. It is very benign and usually tolerable for everyone.
You don’t actually need to seal your grout though, other than with something breathable that might make it easier to clean and to prevent staining. On this topic, I take expert advice from contractor Mike Holmes and architect Cheryl Ciecko. Your waterproofing layer is behind the tile (see the section on Schulter).
Corinne Segura is a Building Biologist with 6 years of experience helping others create healthy homes.
Did you find this post helpful? If so you can buy me a coffee to support the research behind this blog. Thank you!