Mosaic Coaster with Scratched Tile by artist Stefi Morrison, detail shot

When To Use Sanded Grout

This article is about why we recommend “the opposite” of what the tile industry recommends for grouting glass mosaics and mosaics with a standard grout gap. This article also explains how to avoid scratching the glass tile while grouting with sanded grout.

Industry Recommendations

The tile industry recommends using sanded grout for gaps 1/8 to 3/8 inch and adding a coarser grade of sand for gaps larger than 3/8 inch. For gaps less than 1/8 inch, which is what mosaic glass mosaics have, tile manufacturers and industry associations recommend using non-sanded grout.

At Mosaic Art Supply, I have always recommended using sanded grout for everything except mosaics with hairline gaps between the tile. Why the difference? There are three reasons.

Plaques not Walls

Many of our customers are making mosaics on small movable surfaces like plaques or tabletops not walls or floors, and these smaller mosaics are subject to being dropped and impacted and vibrated and flexed more than an architectural surface. The sand provides tensile strength and helps the grout not be knocked out of the gaps as easily.

How Wide Is It?

Most novices tend to use wider gaps than they intended to use or estimate they used. If they actually measured the gaps, they would find that the gaps are actually larger than what they thought for two reasons.

First, most people are bad at estimating small distances. Second, many novices make mosaics with gaps that are inconsistent and problematically large in places. They might not need sanded grout in many of the gaps, but the places that do need the sand tend to need it desperately. Otherwise the grout in those places is prone to cracking and getting knocked out of the gap due to the reasons cited above.

Tough Sand

Sand is harder and tougher (more crack resistant) than portland cement (the grout itself). Many of our customers are making garden mosaics and stepping stones and other outdoor surfaces that see much more abrasion than backsplashes and shower walls. The quartz and feldspar sands used in grout are relatively hard compared to the soft grout, and so they help grout withstand wear and gouging.

Mosaic Coaster with Scratched Tile by artist Stefi Morrison
Mosaic Coaster with Scratched Tile by novice mosaic artist Stefi Morrison. Note that the scratching is not the only sign of rubbing too hard. The grout is also eroded out from the gaps and is significantly lower than desired.

Avoid Sanded With Glass Tile?

Glass tile manufacturers recommend using non-sanded grout, or at least many of them do, because the sand can scratch glass tile. We don’t. We think the reasons above are more important factors, and it is easy to grout with sanded grout and not scratch the tile if you use a little care.

Keep in mind that the manufacturer recommendations have to work for building contractors installing architectural coverings as quickly as possible. Think about floors that are being walked on by the workers as they are doing the grouting. You can work more carefully than that on an art project, even if it is a large mural.

The Correct Method

There isn’t any reason to fear using sanded grout if you don’t try to scrub the grout into the gaps with a lot of force. Gentle pressure and rubbing from every direction and repetition are needed, not force.

Remember, you can scratch hard ceramic tile glazes and even porcelain if you apply too much force.

The mosaic coasters featured in this article were made by artist Stefi Morrison, who describes herself as a beginner. It was her email about the problem with scratching that convinced me that I needed to write this article and clarify the correct method for working grout into the gaps.

I really like the color harmony in the one below. We don’t sell those glitter tiles, but I like how the clear ones match the grout and make the border look like it is composed of four separate corner motifs.

Mosaic Coaster 2 with Scratched Tile by beginner mosaic artist Stefi Morrison
Mosaic Coaster 2 with Scratched Tile by novice mosaic artist Stefi Morrison. Most of these gaps are sufficiently large enough that the usual amount of rubbing wouldn’t be required or even desired. Some of the gaps are large enough that a swipe is as likely to pull grout out as push it in, and so the final pass has to be done with care.

Note that Stefi’s mosaics has a large enough grout gap that it would be easy to get the gaps packed without a lot of rubbing, but most mosaics have places where the gaps are problematically narrow in at least a few places, and these narrow gaps are notorious for having voids or bubbles under a superficial crust of grout.

These voids are usually discovered only after the grout has hardened and the thin crust crumbles.

That is why rubbing or “working” the grout from every direction is needed. It helps ensure that the grout gets packed all the way to the way to the bottom of the gap.

But you do NOT need to scrub or scour the surface with the wet grout in order to get it into the gaps.

Working Wet Grout

You can accidentally erode the grout out of the gaps you are trying to fill if you rub too hard or for too long.

Work the grout into gaps by rubbing from different directions when you first scoop on the wet grout, not later when you are buffing off the excess and discovering voids or bubbles under thin crusts.

Don’t try to reshape the grout if it is more like drying crumbly dough than wet concrete.

Avoid rubbing too much if your grout gaps are large. Take care during early hazing. Let the grout get fairly hard before buffing.

Make grouting easier by keeping grout gaps under 3/16 inch max and shoot for 1/8 inch.

If you are installing in a wet or outdoor location, you don’t want to have places where tiles touch each other and can’t be packed with grout. Even if the glass tiles touch each other, there will still be a micro gap that needs to be filled.

Non-Sanded Grout

Sunshine Mosaic Portrait by artist Suzanne Coverett Earls.
Sunshine Mosaic Portrait by artist Suzanne Coverett Earls. This is definitely a mosaic where sanded grout would not be desired. The grains of sand are not needed for tensile strength in this case, and some of the grains would be too large to fit in the gap. That would leave them on the surface the whole time you rubbed trying to fill the tiny gaps, and that would increase the risk of scratching.

There are situations where non-sanded grout is preferred or even required, and that is when you use hairline gaps or only have a few incidental hairline gaps in a mosaic that was designed to not have any gap at all, such as in a mosaic icon or plaque that does not need to be grouted in order to keep out moisture.

If the mosaic’s gaps are all tiny, then the grains of sand are not needed for tensile strength, and some of the grains would be too large to fit in the gap. That would leave them on the surface the whole time you rubbed trying to fill the tiny gaps, and that would increase the risk of scratching.




8 responses to “When To Use Sanded Grout”

  1. Loretta Hanks Avatar
    Loretta Hanks

    Thank you so much for this Article. I love art.
    I have been making steppingstones for several years. I haven’t created any lately due to my arthritis.
    I have lots of tiles and now I use them in my resin art.
    Thanks always for sharing information.

  2. Alice Craven Baker Avatar
    Alice Craven Baker

    Excellent article. Even with 8 years of mosaic experience behind me, I appreciate being reminded of grouting “rules”.
    As always, thanks Joe

  3. JOAN Avatar

    Great information as always and a very useful update on what I thought I knew about grouting!
    Thank You
    From Joan[ MosaicArtandMore on ETSY]

  4. miriam sutowski Avatar
    miriam sutowski

    I am very much a novice working with mosaics. I have not been very pleased with my work because of the uncertainty I have as to the kind of grout I need to use and the spacing of my tiles. I so appreciate this article as is really has answered several questions I’ve had and had no idea where to get any advise. Thanks again!

  5. Michele Petno Avatar

    Great article Joe on sanded vs. unsanded grout! In 25 yrs. rarely have I ever used unsanded grout. Since I work with glass 80% of time I have never seen scratches from sanded grout. A soft spatula to spread grout and a damp sponge to smooth the grout has always worked for me. Unsanded grout can be a disaster if chosen for the wrong reasons. You helped many people!!

  6. Anne Avatar

    I have finished a pet portrait mosaic. My dog is a yellow lab. I made her with white, yellow and beige glass. The background is made of a few shades of blue. I was going to grout the dog in beige. I just purchased a colorant kit. I wanted to grout the background in blue. Can you provide advice on how to mix colorant with grout? Can I achieve lighter or darker shades of the colorant? Also, if you can – please let me know how important it is to use a mask when mixing the grout and/or colorant. I’ve recently read that one should always wear a mask when mixing grout. And change my clothes afterwards. True? Thank you.

    1. Joe Moorman Avatar
      Joe Moorman

      Hi Anne,
      For a pigment to be UV resistant and permanent in grout, it is probably a metal oxide or heavy metal oxide, which means you definitely don’t want to breath the dust. They are toxic and exposure is permanent and cumulative. That is why we don’t sell them and recommend artists acrylic paint as a safer alternative (because they are wet and not a powder).

      All that being said, as an engineer and scientist, and as an artist, I have regularly worked with toxic and dangerous substances, and it is possible to do so safely.

      As far are as mixing them with grout to get the color you need, I would mix up a small batch of grout and divide it into 3 or 4 lumps and them mix in different amounts of pigment into each lump. I would let those harden before I evaluated them because grout is lighter in color when it hardens.

      I hope this helps,

  7. Carol Buckland Avatar
    Carol Buckland

    Thank you so much for this information. I am a “newbie” and did not know about sanded/non sanded grout. Now I know why why grout dries out, bits fall off.

    Would sanded grout be better on anything to be kept outside, for example a bird bath.

    I have got a heap of tiles at home, but i have been disappointed in my effort and it is a bit too expensive to make stuff up, after stuff up. I really appreciate your explanation about grout.
    Kind regards
    Carol Buckland

Leave a Reply

Your email address will not be published. Required fields are marked *

This site uses Akismet to reduce spam. Learn how your comment data is processed.