Mosaic Redwoods by Tracy Kaplan Grouted.

Choosing Grout Color Using Tile Test Swatches

Tracy Kaplan recently emailed us a picture of her FIRST mosaic, and it is nice solid work, impressive even, especially considering that her instructor gave her some problematic advice concerning the grout color.  Tracy’s teacher had recommended a chocolate or nutmeg colored grout, but Tracy wisely considered how a dark brown might cause adjacent tree trunks to no longer be distinct and separate.

Perhaps Tracy’s instructor had meant a lighter shade of those browns, but I still think that those could have caused problems with the adjacent tree trunks.

Most likely, the instructor only saw a portion of the mosaic without adjacent tree trunks. Tracy admits that she only finished about an eighth of the work during the course and spent many months afterward working to complete it.

If so, this is yet another example of how artistic advice isn’t one-size-fits-all and can be counterproductive or even disastrous if the advice isn’t specific to a particular artist or even a particular work of art in its entirety.

Fortunately, Tracy emailed us for advice.

Mosaic Redwoods by Tracy Kaplan Pre-grout.
Mosaic Redwoods by Tracy Kaplan Pre-grout.

Two Methods

Our response came from the general guidelines recommended in my article on how to select a grout color, which gives you two options:

  1. Take some of your tile (or the finished mosaic if small) into a building material store and compare the tile colors with the grout color swatches.
  2. Make some tile test swatches on a scrap piece of plywood and grout them with two or three different grout colors you are considering.

With either option, you should include some tile from all the colors used in the mosaic. Tracy chose the second method.


If either of these methods seem like overkill, then remember that our perception of color is determined by the colors adjacent to it, and that the same color can look radically different in two different situations. Even experienced fine-art painters don’t know how a color will look in a painting until they actually apply it to the canvas with the other colors.

Grout Test Color Swatch
Grout Test Color Swatches. Note the dark grout in the center of the top left swatch. That dark grout is problematic as is, but if it had a brown hue, the tile would not be visually distinct at all.

Tile Test Swatches

Tracy actually used much more tile than I would have for some quick test swatches, but that is OK if you recycle the tile afterwards. (You can scrape the tile off with a paint scraper if you soak it, and you can nip the grout off the tile with a Mosaic Glass Cutter.)

When in doubt, use as much tile as you think necessary, but each of these swatches could have been 5 or 6 tiles.

In the photo above, note the dark grout in the center of the top left swatch. That dark grout is problematic as is, but if it had a brown hue, the brown tile would not be visually distinct at all.

Mosaic Redwoods by Tracy Kaplan Grouted.
Mosaic Redwoods by Tracy Kaplan Grouted.

Tracy’s Choice

Tracy chose a 50/50 mix of a cool light grey and a warm medium grey. I think the exact hue wasn’t nearly as critical as the shade, and I think the shade she chose is spot on for creating a forest sunlight effect.

The vegetation in a forest may have color, but on a sunny day, all that vegetation is a lacy silhouette for the sunlight coming around it and through every little gap. A light-colored grout such as Tracy chose was critical for making this happen.

A dark grout would have made a heavy outline around each leaf and robbed the clusters of leaves of “highlights” and light shinning through in many filigree places. The clusters would become opaque clumps with less depth. The trees would lose their sense of height and appear right overhead instead of soaring overhead.

If you wanted the forest to be deeper and darker by using a dark grout, you would have to build in all the filigree in the canopy using tile instead of suggesting it with the grout line. Else you lose detail and depth.

Hue? I don’t think a warmer hue would have worked because it needs to suggest blue sky in places, but in all probability, the mosaic will be displayed indoors in warm indoor light anyway.

The composition is strong with lines converging at the vanishing point: a broken wedge of blue sky over a wedge of trail and a wedge of forest framing either side. All wedges have a sense of depth, even the forest on either side because we can see sunlight on the forest floor suggested by the light grout.

I really like this mosaic, and I almost never like mosaics with light grout. I’m glad that Tracy used our recommended technique to choose a light grout that works well, especially since my general advice for grouts is that darker tends to look better.

Changing Grout Color With Paint

If you want to change the color of a grout line in a finished indoor art mosaic, you can do that with artist’s acrylic paint applied via wipe-on-wipe-off using a rag before the paint can dry on the glass. The paint should stick in the porous grout.

I recommend  diluting the paint with acrylic media to make a water-based “grout stain.” You can also apply undiluted paint for a more opaque covering of the existing color, which might be simpler for most people.

I recommend experimenting on any piece of scrap material to figure out colors and dilutions.

I recommend testing on a grouted tile swatch before applying to the mosaic to see how it actually looks on the grout.

I recommend Yellow Ochre and Burnt Umber. Both are UV resistant mineral pigments and considered non-toxic. They also make great stains.

You can also use Ivory Black and Titanium White to make hue-neutral grays of every shade, but a wide range of colors are available, and you can make more interesting grays too.

I would avoid toxic Cadmium Yellows but Nickel Yellows are considered safe.

I would avoid making my grout paint more intense in color than the tile colors.

Grout Gap

TIP: If you want to minimize the color impact that grout has on your mosaic, use a smaller grout gap.

Outdoor and wet mosaics might need a standard grout gap to ensure that they are filled with grout to keep out the water, but indoor art mosaics that aren’t architectural coverings don’t need any grout gap at all, and you can press the tile as closely together as possible.

Small Projects for Beginners

TIP: First art projects in any new medium should be small, particularly with mosaic, because mosaic takes some work. You don’t want to find yourself working on something that has a long way to go when you already wish you could change decisions you have already made.

BUT with the photograph Tracy chose as a model, a larger size was needed to make rendering all the detail. Rendering all that detail in a smaller size would have been more work and more tedious work, not less.

If you choose to do a small mosaic as a first project, make sure you choose a model that can rendered at that size.

My rule of thumb is to look at the smallest detail in the model and render that detail in tile on my desk using the smallest tile I can cut and work with comfortably. From that starting point, I am able to gauge how large the overall mosaic should be.






20 responses to “Choosing Grout Color Using Tile Test Swatches”

  1. Patricia Crain Avatar

    Thank you, Joe. You are very kind to share this information.

  2. Marguerite Trail Avatar
    Marguerite Trail

    Great article, very helpful!

  3. Jill Gatwood Avatar

    Great article on grout color, which can be a challenging issue for even very experienced mosaic artists.
    And excellent piece, Tracy! Very impressive. I’m glad there is a picture of it ungrouted, too, to demonstrate the power of grout color.

    Like Joe, I usually lean toward using a dark grout in most mosaics, but I have to admit that a few times, students of mine have ignored my advice and really saved a piece by using lighter grout than I recommended. Other times, either all-over dark or light grout became problematic for a piece and we ended up using different grout colors for different parts of the picture. I also always recommend doing test swatches and also using smaller grout lines to minimize the impact of grout color on the design.

    Something I’m curious about is sanded vs non-sanded grout. I always use sanded grout, whether for indoor or outdoor mosaics and no matter how tight the grout lines are. I haven’t used non-sanded grout, but I’d like to hear from other mosaic artists about the pros and cons of each.

    1. Joe Moorman Avatar
      Joe Moorman

      Hi Jill!

      When we receive an email from someone whose grout had problems cracking or being too soft, it is usually from someone who used non-sanded grout. Grout needs sand for the same reason that concrete needs gravel. It makes it tougher (resistant to impacts) and stronger. It increases tensile strength.

      I think the only valid use of non-sanded grout is filling hairline cracks.

      As always, I am talking about traditional grouts made from portland cement and not the new expensive pre-mixed epoxy and urethane grouts. I don’t use those. Traditional grout can be replaced over the years, but epoxy and urethane grouts might not age gracefully and yellow and crack in sunlight.


  4. Karen Brow-Meier Avatar
    Karen Brow-Meier

    These posts are very helpful– I feel like I’m taking a really good class and getting all the “wisdom of the trenches” from en expert. Thank you for sharing your experience and knowledge.

  5. Yolanda Wroe Avatar
    Yolanda Wroe

    I really appreciate the instructions you provide. They are invaluable to me as I am just a beginner but I seem to have a sense of what goes with what — fortunately!

    I buy lots of your mosaic tiles as you have a nice selection.

    Yolanda Wroe

  6. Patricia Stevens Avatar
    Patricia Stevens

    Can I send you a photograph of an orb I’ve mosaiced and already grouted for your comment on grout color?

    1. Joe Moorman Avatar
      Joe Moorman

      Sure thing. Please email it to us at

  7. Ashley Avatar

    That mosaic is stunning!

  8. Joe Avatar

    Beautiful piece. The light grout showz the dappled light found on a wooded trail. Just delightful!

  9. Mercedes Romo Avatar
    Mercedes Romo

    I recommend painting a grout line with
    Acrylic paint AFTER the sealer is applied
    Otherwise the paint will stand out.

    1. Joe Moorman Avatar
      Joe Moorman

      Hi Mercedes,
      It sounds like your method/sequence ensure that less paint sticks to the grout. Rather than compromising the bond that the paint can make with the grout, it is probably better to dilute the paint with acrylic medium to make it look less intense.

  10. James Britt Avatar
    James Britt

    Greetings. As to the grout conversation this is a method I sometime use. I would lay the completed project on a table mosaic side up. Then I use some dry grout to fill a portion of the mosaic. After brushing lightly and cleaning the surface off the remaining grout fills the spaces. This is what the finished piece will look like. I then vacuum the grout out of the spaces and proceed. It is easy to try several colors.

    1. Joe Moorman Avatar
      Joe Moorman

      Hi James,

      That is a great idea.

  11. Shreevalli Avatar

    Can we use 4 to 5 different grout colour in one mosaic piece?
    Should it be done in several phases?

    1. Joe Moorman Avatar
      Joe Moorman

      Yes you can, but grout works best when the tiles are the source of color and the grout line serves visually only to make individual tiles stand out. I suppose you would need to do each color grout as a separate session to avoid getting it in zones where you didn’t want it.

  12. Rhonda Croghan Avatar
    Rhonda Croghan

    Whats your opinion on un grouted pieces? I’ve done stained glass mosaics on several repurposed old wooden windows. I delayed grouting a finished piece b/c I could see that the glue under some pieces of glass wasn’t dry. I moved on to another project & found that I like the open feeling of the ungrouted piece. I’ve since completed about 5 or 6 more projects & haven’t grouted any except the very first one I had finished. They’re all displayed indoors & wouldn’t really even consider them weather proof. Long question, but is the structural integrity of the piece compromised because I chose not to grout?

    1. Natalija Moss Avatar
      Natalija Moss

      Hi Rhonda, mosaics do not need to be grouted if they’re on permanent display indoors away from moisture. You can use a clear silicone adhesive such as GE Silicone II for glass-on-glass mosaics using stained glass. It will cure fully when underneath the stained glass, unlike Weldbond.

  13. Pam Lackie Avatar
    Pam Lackie

    I’m having a heck of a time keeping black grout from seeping into the back edges of more transparent stained glass. This ends up looking like a bit of a mess when all is said & done with black bubbles, black streaks, etc. showing under beautiful mosaic art glass. I can’t figure out what to do about this. I allow the glue to fully dry (I think) before grouting, but it still seeps. ??

    1. Joe Moorman Avatar
      Joe Moorman

      We recommend GE Silicone II for glass-on-glass mosaics because a water-based adhesive doesn’t fully harden between glass.

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