Non-Toxic Grout and Thinset Mortar

I just had the tiling done in my tiny house bathroom and in the process learnt a lot about chemical-free grouts and thin set mortars.

DITRA over the first layer of thin set
I used Custom Building Products' Thin Set Mortar which is zero-VOC (and mildewcide-free). It had a bit of a smell when wet but seemed fine once dry. You want a water-based thin set that is not mixed with latex or acrylic additives. Avoid the toxic epoxy thin sets. Avoid mastics as well.

Another non-toxic thin set to try is C-Cure 911 which does not have synthetic additives

These non-toxic thin sets are more prone to cracking than ones with additives. 

Over the first layer of thin set I used Schluter DITRA, an uncoupling membrane that will help prevent cracking when my tiny house moves.

If you just need a waterproofing membrane use Schluter Kerdi. These are both made out of polyethylene and do not have a smell.

My completed tiled bathroom!
I used this grout, the same brand as the thin set, which is also zero-VOC and contains no mildewcides or antimicrobials. It comes in sanded and unsanded and in different colours. (unsanded is for marble and certain tiles). It barely had a smell, though it does have polymers (probably latex) which may not be tolerable to some.

If that one is not tolerable, Hydroment is recommended for people with sensitivities. However, it has a small amount of latex additives and contains mildewcide. 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.

Sanded grout contains silica (the same substance as glass) which is harmful to breathe in when in dust form. Use a N95 mask (or better) when mixing it until it is fully mixed. This is completely safe when it is no longer in dust form.

I used concrete tiles from Morocco. For more on choosing non-toxic tiles see my post on bathrooms.

I sealed the concrete tiles and grout with AFM Safecoat Penetrating Water Stop. Grout is porous and should be sealed regularly to prevent mould. If just sealing grout (and not tiles) use AFM Safecoat Grout Sealer.


  1. 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.

    1. 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

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

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

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

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

  4. 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?

    1. 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.

    2. 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.

    3. 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.