Updated Spring 2020
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Non-Toxic Thin-Set Mortar
Thin-set is the bonding layer that goes down under your tiles. Concrete based thin-sets are the safest type and are also easy to source.
Unmodified Thin-set (no Additives)
An unmodified concrete based thin-set that is not mixed with acrylic-latex additives.
The unmodified type 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 additives, and you have to check if your application requires polymers.
On walls thinset usually has some acrylic-latex additive. Ceramic tile doesn’t need much acrylic-latex, porcelain tile needs more.
Most chemically sensitive folks would want to avoid the toxic epoxy thin-sets and most mastics. Although there are some safe and tolerable tile glues like AFM 3 in 1.
Thin-set mortar is also known as dry set and dry bond.
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).
Membranes for the Walls
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).
Integrated Membrane Boards
Instead of using the membranes over concrete backer boards (backer boards discussed in this post), you could use Kerdi Boards or Wedi Panels. Test for tolerability before proceeding, they are not odor-free. But they will be behind the thin-set, tiles and grout, which will be safe for most people.
These integrated membrane wallboards help simplify things by replacing concrete backer boards + membrane with just one substrate that is easy to waterproof.
The panels are made of non-toxic 0-VOC polystyrene with a plastic 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, these grouts can be found at regular building supply stores.
I used Custom Building Products Polyblend grout, the same brand as the thin-set, which like the thin-set is 0-VOC and contains no mildewcides or antimicrobials.
It barely had an odor, though it does have polymers (listed as EVA). Almost everyone does well with this one.
Mapai Keracolor (U and S) is another brand that lists the polymer – we know it is EVA.
If those don’t work for you, Hydroment is also recommended for people with sensitivities. However, it has a small amount of latex additive (this usually refers to acrylic) and contains an antimicrobial, which appears to be silver-based.
Many Laticrete products use Microban, which is this case almost certainly refers to Microban’s silver antimicrobials.
Make Your Own Grout
If you need to avoid all additives, you can make your own grout with Portland Cement mixed with sand, lime, and water for a totally chemical-free option.
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 to chemicals will probably want a concrete-based grout (like those above) and then see which additives if any 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 against your sensitivities.
Common polymers in grout include: latex-based polymers, 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 means you can 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 will depend on your specific project. I don’t consider most of these polymers to be toxic.
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 some don’t. 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 its 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 out QuartzLock; this won’t be tolerable for everyone. It is a urethane-based grout, not cement, and provides more waterproofing.
This grout is significantly higher in offgassing and it should not be necessary in most applications to use this over cement-based grouts.
Your waterproofing needs to be done properly behind the tiles.
There are applications that would call for a waterproof grout.
Epoxy grouts are also waterproof, and may be selected when a clear grout is specified.
Non-Toxic Tile Types
I used concrete tiles from Morocco. For more info on choosing non-toxic tile types, my post on bathrooms goes into the most detail.
Tiles don’t generally have any offgassing. Lead is the biggest concern.
Non-Toxic Grout Sealers
If you are just sealing the grout (and not the tiles) you can use AFM Grout Sealer. It’s 0-VOC and is one of AFM’s most tolerated products. This is a potassium silicate product also known as liquid glass. It’s a breathable densifier (which is what you want).
Custom Building Products grout sealer is another one that many people do well with, less than 1 g/l VOCs. This also looks to be a potassium silicate.
ECOS, a well-liked brand, has a stone sealer that is used on grout. They do not disclose any of the ingredients in this product so it’s not possible to know if it is a breathable densifier or topical coating.
Sodium, potassium, and lithium silicates (aka water glass or liquid glass) is a very safe product that also leaves the grout breathable. It is a densifier so it makes it easier to clean and less likely for dirt grime and mold to get embedded. It’s not intended to be waterproof.
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). The grout should be breathable.
Corinne Segura is a Building Biologist with 6 years of experience helping others create healthy homes.
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