Whether you need a grout sealer depends very much on the situation. A grout sealer could actually do more harm than good.
For that reason, I will list out the non-toxic sealer options by application and then by type of sealer.
The densifiers are the most tolerable least toxic option, they are a very benign product. Topcoats of acrylic or polyurethane do have some odor and offgassing at first, but the offgassing comes to completion in a short time.
There is also the possibility of going with a natural product, some natural penetrating oils can be used on concrete grout.
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1. To Seal Grout in Tiled Showers
In wet areas, you generally want to use a breathable sealer. Both Mike Holmes and Cheryl Ciecko recommend this approach to keep the grout breathable and allow water to dry out to the inside.
Your waterproofing is done behind the tile.
You can keep the grout unsealed. If you must seal it, use a liquid glass sealer which still allows some breathability.
AFM Grout Sealer is one option, It’s zero-VOC and is one of AFM’s most tolerated products. It has almost no odor at all even when wet. This is a potassium silicate product also known as a liquid glass densifier. It does not change the look of the grout at all.
A densifier makes it easier to clean and less likely for dirt, grime, and mold to get embedded. It’s not intended to be waterproof.
You could use a DIY/homemade option by buying liquid glass and applying this. However, I would caution against that because it’s easy to end up with a white film if you buy just any liquid glass. I would buy AFM Grout Sealer, or another brand made for grout, and follow their instructions so you get a even (and invisible) finish.
2. To Seal Grout on Tiled Floors
If your tiled floor is on a concrete slab (on grade or below grade) then Cheryl Ciecko also recommends keeping that breathable so that the concrete can dry to the inside.
Use AFM Grout Sealer is a no VOC product that does not change the look of concrete-based grout at all.
If your tiled floor is on an upper level of a house or apartment building and the floor below is the same temperature (more or less) as your space then you can use a tile sealer that blocks moisture.
You can still use a densifier but you can also use:
ECOS Stone Sealer
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 how breathable it is exactly. It is zero VOC.
AFM Safeseal is an acrylic coating that can be mixed into a dry mix concrete grout (with the water) instead of adding a topical grout sealer.
For a strong topcoat sealer, you can also use a water-based polyurethane like Earthpaint Nanotech.
You can also use a natural oil on concrete-based grout. I have been experimenting with 100% natural tung oil and have so far have liked the effect. It certainly darkens the concrete by quite a bit.
3. To Seal Tile on a Backsplash
You don’t necessarily need to seal grout on a backsplash since it doesn’t usually get that damaged. But if you do want to seal it that can provide some stain proofing.
If your tiled wall is on an exterior wall and you use AC inside the wall should be kept breathable. The most that you should use is a densifier.
Use AFM Grout Sealer.
Acrylic and Polyurethane Sealers
If your tiled wall is not on an exterior wall, or you don’t use AC inside you could use a densifier or something that blocks more moisture like ECOS Stone Sealer, Safeseal mixed into the dry powder at the time of application, or Earthpaint Nanotech.
All Natural Sealer
You can also use a natural oil on concrete-based grout. 100% natural tung oil leaves the grout partially breathable (similar to densifiers) but darkens the look quite a bit. It takes some time to fully cure but provides good protection against stains, especially oil stains.
4. To Seal Tiles on a Countertop
In this scenario, I would want the most protection from moisture and stains as possible.
If you can, mix an integral sealer like AFM Safeseal into the dry mix grout and follow that with a topical coating like Earthpaint Nanotech. If that is not possible use AFM Grout Sealer first, followed by Nanotech.
The Natural Option
You can also go all natural with pure tung oil. This darkens the look of the concrete-based grout and will certainly give you particularly good protection from oil-based stains. Tung oil is really quite durable for a natural choice. You cannot use a synthetic sealer over this, and it likely won’t work over a synthetic sealer since it needs to soak in to work.
Choosing non-toxic grout and mortar
Non-toxic waterproofing in bathrooms
Corinne Segura is a Building Biologist Practitioner with 8 years of experience helping others create healthy homes.