Non-Toxic Grout and Thin-Set Mortar

Updated October 2019

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Non-Toxic Thin-Set Mortar

Non toxic underlayment with chemical free grout
DITRA over the first layer of thin-set
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 odour 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 you application requires polymers. Thin-set mortar is also known as dry set and drybond.

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

non toxic no offgassing odourless underlayment
Schluter Kerdi 
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 a odour 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 mould 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 odour-free.

These simplify things by replacing concrete backer boards + membrane with one layer that is easy to water proof. The panels are non-toxic 0-VOC polystyrene with a membrane already integrated.

Concrete Based Non-Toxic Grout

non toxic tiles with non toxic grout and grout sealer
My completed tiled bathroom!
Concrete grouts are the safest grouts and are generally non-toxic. You don't need to go to a green building store here, there 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 comes in sanded and unsanded and in different colours. (Unsanded is for marble and certain tiles). You can find this at Home Depot as well as Amazon.

It barely had a odour, though it does have polymers which 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.

Laticrete also makes a number of 0-VOC grouts and thin-sets that may work for you. It's a matter of finding out which additives work for you and if additives are required for your application.

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?

is thin set, grout safe? why is there a prop 65 warning Sanded grout and thin-sets contains 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 a 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 cements contain 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. You waterproofing layer is behind the tile (see the section on Schulter).

Corinne Segura is a Building Biologist with 5 years of experience helping others create healthy homes.

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Anaphylaxing said...

Pretty tiles! Great post.

Mboris said...

Very informative post and site. Thank you for sharing.

One of the issues I have is finding mortar and grout that are low in VOC as well as chemical exposure but at the same time without any ingredients labeled as carcinogens. Every product that I have found contains some carcinogen or toxic ingredient. Are there any alternatives that you have found on this. Silica sand seems to be the primary issue on the most used ingredient across this products. Hope someone has found an alternative product(s) that they can share.

Corinne said...

Silica is only harmful when you breath in the dust otherwise it does offgas anything at all (i.e. glass). You could use a really good respirator and stay away when the mortar is being mixed

Unknown said...

I had the same concerns reading the MSDS of the products. Happy to hear once cured .... that is safe.

The Kremers said...

I already have QuartzLock urethane grout. Do you think that product would be okay to use to re grout bathroom tiles?

Corinne said...

It has a VOC level 35 g/L, so up to you. That is low VOC.

RamblingRose said...

How have the tiles held up after moving the TH? any cracking of the grout?
Thanks for the informative article!!

Corinne said...

No, no cracking after the move!

Unknown said...

What about caulk? Is there a completely nontoxic zero voc one I can use around my bathtub where the water will be touching it every day?

Corinne said...

I have a post on that

truth naked said...

I couldn't find it. Can you please direct me to it somehow?
Also, why doesn't polyblend advertise their grout as non-toxic? Also, I have old tiles in my apartment. They were put there 67 years ago when the building was first built. When I said this to the worker at home depot he said I have to get the non-sanded grout for the area around my bathtub, saying sanded is usually used for floors. I bought sealer from green planet paints. How does this sealer compare with the one you recommended? Thank you.

Corinne said...

Here it is

I do not know of a sealer by Green Planet Paints. Send me the link that you have.

A lot of products that were never toxic don't advertise as such. The same thing goes for drywall mud and until recently drywall too. I suspect certain grouts will seek green certifications soon.

truth naked said...

Thank you. Your posts are very informative and useful.
I couldn't copy the link here, but if you go to and once there click on green coatings and toppings you'll see the description. is their sister site.

truth naked said...

This blog is so informative, but the grout recommended above says on the back of the package that I contains chemicals known in state of CA to cause birth defects or something to this effect.

Corinne said...

Silica. In dust form it is harmful. Don't breath it in in dust form just like any product containing silica. Completely safe once dry. Glass is silica. Think of glass in solid form.

truth naked said...
This comment has been removed by the author.
truth naked said...

Premixed version of same exact product says the same.

truth naked said...

Premixed version of same exact product says the same. Is it just as safe to get the Premixed one then?

truth naked said...

Also I read somewhere on this blog that polystyrene is a safe material to use. An article I read on written by a PhD chemist appears to state otherwise... yet the alternatives suggested are also not green.

Corinne said...

I wouldn't use the premixed version because of the VOC levels. The California warning is on Ethylene Glycol/
Diethylene Glycol Monobutyl Ether

Corinne said...

I consider that to be a safe product other than the flame retardants. Discussed in detail in the post on insulation. Not sure which article you are referring to though. In terms of environmental effects it's not considered the greenest product but I look at effect of its use in homes.

PJames said...

Corinne.. you suggested avoiding latex and acrylic additives in thonset. I noticed when looking at the MSDS sheet for Benjamin Moore Natura paint that the base is acrylic latex, can you explain the difference. Can all be most confusing.

Corinne said...

Many people cannot tolerate the acrylic paints at all though I suggest the ones that are 0 VOC and best tolerated. The additives in grout are not disclosed so I can't do a direct comparison between the ingredients. But some very sensitive people would have trouble with acrylic.

PJames said...

I have a floor I thought was concrete, I planned to paint it with SafeCoat concrete paint, but it turns out the floor is Gyprete. I want to tile using thinset but can't even walk on the surface because the dust coming off, it needs to be sealed. Talked with tech reps at both SafeCoat and Benjamin Moore, neither is sure they have a product that will adhere to it, and the 046 BM primer they think might work has mildewcide. Any suggestions?

Melody said...

Find the least toxic mortar and grout possible and then use a sealer like AFM SafeCoat Grout Sealer, or even their Hard Sealer and Safe Sealer products, concieved especially for stopping off-gassing. They seem to be 0 VOC , formaldehyde etc.
There surely are other eco-sealers available if you check, so it can be an effective solution for the off-gassing as well as mold prevention for grout, since mold is also a carcinogen and super-toxic in many other ways.

lela said...

Does Schluter (same brand as the ditra you used) all set (their thinset) contain vocs? I would like to use it, because if you use both ditra and their brand thinset there is a lifetime warranty. However I haven't been able to find online if it contains voc's.

Corinne said...

ALL-SET is modified so it contains unspecified polymers. They don't list the VOCs but it would likely pass as 0 even though the super sensitive cannot tolerate many or all polymers.

Cheyenne Hanes said...

very glad i came across this page, we have a baby and are looking to redo the vinyl to tile and was wondering what your opinion was on which brands would be less toxic(no vocs and other harmful chemicals to babies)for us to use! need help picking a back board, mortar/thin set, grout and a sealer if we need it. hoping you could help! thank you.

Cheyenne Hanes said...

What do you think about forbo marmoleum 885 adhesive, how safe is it compared to the ones you listed!

Corinne said...

Brands are listed here. There is also a post on bathrooms with backerboards and tiles.

Corinne said...

On paper it looks fine.

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