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The secrets of using thinset for mosaics by Julie Sperling

Drinking from a firehose: flood prone yet drought stricken. Photo and mosaic: @Julie Sperling

I am delighted to present a guest post (my first) by award winning Canadian mosaicist Julie Sperling about using thinset for mosaics. Julie’s work stands apart in being both fiercely beautiful and intelligently polemical. In her hands mosaics move out of the decorative realm and into a hybrid world where art meets politics meets activism. Using a wide range of tesserae and found objects from the traditional (smalti and limestone) to the unusual (grafiiti paint layers) and the bizarre (flue damper), Julie explores the subject of climate change and our human response to it through mosaics which make your heart sing and your thoughts linger.

using thinset for mosaics
Dialogue, the Burden of the Message. Photo and mosaic: @Julie Sperling

How does she do it? you ask. I have often wondered. No one (probably least of all Julie) could precisely explain the process by which she interweaves her materials with the subject matter to create works of art but Julie’s work is impressive on many levels, including its sheer technical virtuosity. In many of her mosaics the substrate is part of the piece rather than just a surface to be mosaicked. It’s a pause, a space, a frame, it allows her to open the work up to infinite suggestions, to make emphases, to change direction and to add permutations and explorations both on and beyond the ‘canvas’. See how she does it here in Heat (Each Decade Hotter Than The Last) where the central ‘graph’ is separated by a perfectly balanced border of thinset:

using thinset for mosaics
Detail from Heat, Each Decade Hotter Than the Last. Photo and mosaic: @Julie Sperling.

Thinset (or mortar) isn’t an attractive word or in most people’s books the most appealing aspect of mosaics, but in this blog post about using thinset for mosaics, Julie shows us how this most mundane of substances can be used to create stunning effects. Many thanks Julie!

using thinset for mosaics
Flip the system; Amplified Change. Photo and mosaic: @Julie Sperling.

Julie’s Tutorial: Using Thinset for Mosaics

Before we start, a caveat: This is what works for me, but it is by no means the only (or best) way to do it. It is the method I have learned through trial and error to compensate for my complete lack of palette knife skills. So proceed with caution, take it with a grain of salt, use at your own risk, etc.So, how do I get the thinset in my mosaics smooth, both between my lines and tesserae and in the background?

First, my go-to implements for the task: an array of paintbrushes, spatulas, and palette knives, as well as water and a rag. And don’t think I only use the brush/blade end! Anything is fair game, including fingers.

using thinset for mosaics
Julie’s thinset smoothing tools. Photo: @Julie Sperling

Now, if you want to save yourself work, make sure your initial bed of thinset is as smooth as you can make it. Just like taking a good photograph to start will save you time and frustration in post-production, touching up a smoothish surface is much easier than trying to fix an area riddled with bumps and ridges and lumps later on. A pass or two with a clean palette knife (wiped with a damp cloth) will make your life much easier. Admittedly, though, I usually skip this part or, at best, make a half-hearted attempt to get a nice smooth bed. Why? Because I’m not really great at using a palette knife and because fixing it later doesn’t particularly bug me.

Smooth thinset in between lines and tesserae

When I weave my lines, I like the thinset to be smooth, especially where there’s more open space. I have no reason for this other than personal preference. Once I set my tesserae into the thinset, I leave them for a bit before attempting to go in with my various implements to smooth it out. I’ve found it’s far easier to work with the thinset once it has set up a bit—it’s less sticky and far more compliant. I just pat it / brush it as best I can, mostly with a dry brush or other tool (or, more frequently, the blunt end of a tool).

using thinset for mosaics
Patting and brushing the thinset into place using both ends of the paintbrush, once it has set up a bit. Photo: @Julie Sperling

Sometimes the thinset dries shiny and smooth. I don’t particularly care for this look, so I will take a slightly thinner mix of thinset at the very end (when I’m cleaning up the background) and just dab it into the small spaces, being very careful not to get any on the tesserae.

using thinset for mosaics
The shininess of this dry thinset really bugs me, so I always go back and fix it. Photo: @Julie Sperling
using thinset for mosaics
A steady hand and a small paintbrush. Dabbing a bit of thinset onto the shiny part is an easy albeit nerve-racking fix. Photo: @Julie Sperling

Smooth thinset as the background

I save this step for the very end. I spread my thinset on the background, usually in stages (I find doing one side at a time works well for me). I try not to put it on too thick (because then it just squishes around when I try to smooth it with my brush) or too thin (because then the roughness of the substrate comes through).

using thinset for mosaics
Covering the background with thinset. No need to be careful or make it look pretty, because it gets fixed with the damp foam brush. Photo: @Julie Sperling

Then I take a foam brush, wet it with water, and squeeze the excess out with my cloth so the brush is just damp—this is very important, because if your brush is too wet you risk getting white splotches on your thinset once it dries.

using thinset for mosaics
Make sure your brush isn’t too wet. Trust me. Photo: @Julie Sperling

I lightly brush the thinset with my damp brush to smooth it out, taking care to keep my brush strokes going in the same direction. I find that shorter, quicker strokes work better for me. When too much thinset accumulates on my brush, I rinse it, wring it out in my cloth, and keep going.

using thinset for mosaics
A barely-damp foam brush is your best friend when smoothing out your background thinset. Photo: @Julie Sperling




Sometimes I have to switch to a smaller brush to work closer to the tesserae, but normally I can make it work by angling my foam brush this way and that to follow the curves of the outer tesserae.

And that’s it! It really all boils down to working as neatly as you can from the start to save yourself the headaches later on, making sure your brush isn’t too wet, and being patient.


  1. Kathy Florence

    Thank you! I’ve been anxious about working with thinset and I think this has given me a bit more confidence I just need to jump in a try it

  2. Excellent tutorial! Thanks for generously sharing your method Julie! And Helen for all your other tutorials which are very clear and helpful to me as I am a beginner in mosaics.

  3. Fiona McAlevey

    I am so glad to have found this website! Wonderful, clearly-explained (in words and pictures) and enjoyable to read. Thanks for your generosity in sharing this.

    1. I use BAL Turbo Set Tile Adhesive from Topps Tiles which comes in grey and white and then you add pigment (available from art shops)but of course it will depend which country you live in! I’ve heard that others recommend BAL Blue Star Fibre Enhanced Tile Adhesive which comes in tubs and is ready mixed. I hope that helps.

  4. lyli rossett

    Vi seus trabalhos no Pinterest! Achei maravilhosos, vc eh uma artista nata!!! Parabens!!! Amei sua arte musiva!!!!

  5. Andrea

    How do you use the adhesive with the thinset ? Do you adhere the tessarie first ? Lovely work thanks for sharing

    1. Hello Andrea. The key thing you need to know is that thin set IS adhesive. I don’t know where you are based but in the UK we call it tile adhesive (and I use BAL’s Turbo Set Flexible Tile Adhesive for Walls and Floors available from Topps Tiles) and in America it is called thin set. I am in the middle of making a new tutorial about the basics of using thin set and will fill you in with all the details but basically you follow the manufacturer’s directions on the packet and make a paste which you apply to your substrate and then push the tesserae one by one into the adhesive. I hope that helps! Good luck with your mosaicking.

  6. Patti

    So is using grout just an artistic choice? If the tesserae stick well with just thin set, what is the function of grout?

    1. You use grout or not depending on what method you are using. If you are using the thin set method you don’t need to grout because you are pressing the tesserae into the thin set so they are self grouted and held in place by the thin set. I will publish a new blog post at the end of this week about the basics of thin set so you can see what I mean. I hope you find it helpful, Helen.

  7. Cem

    Thanks for this very informative tutorial. It helps demystify things a little. What beautiful work you do Julie and thanks Helen for hosting this. Continued success.

      1. Aileen M. Gonzalez

        I can’t wait to try the method..the explanation is great to understand and follow it. I’m used to make a mess everyday in my art room so I don’t care, ha,ha
        Thanks so much..

  8. Cynthia Lea

    What do you use to dye your thin set? Your dark grey or black looks so nice and rich. So often colored concrete dries a faded color.

  9. This is interesting, thank you for sharing. I’m guessing the thinset is colored? And the artist works in small batches to event out the thinset and lays out the thessarae individually in place to form her lines and uses brushes to smooth out background. I’m guessing that there is no grouting of the pieces involved in the end?

    1. You’re welcome! Yes, the thinset is coloured and yes Julie works in small batches laying her tesserae into the fresh adhesive and doesn’t grout at the end because the thinset acts as a grout by coming up between the individual tesserae and holding them in place.

  10. Randy

    Very interesting. I have been gathering many different colours of stone here in BC and have a diamond wet saw to cut the stone into slabs to speed up the process of making the tesserae on my hammer and hardie. I have a few projects in mind that will work well I hope with the colours of rock that I have collected. After reading your post I am anxious to finally get started learning how to do mosaics. Such a beautiful ancient and durable art form that can add real beauty to a home.

  11. Naomi

    I’m so thankful to find this method, because I’m wanting to use thin set as a background for my mosaics and now I can! Can this method be used for outside mosaics? My mosaics will be hung outside in my garden.

  12. marlene silcocks

    i’m unhappy with my background color. it dried way to light. i wanted a very dark blue.
    can i grout over it?

    thanks. marnie

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