Outdoor School Mosaics

Recently I received an email from an art teacher whose school mosaic project was an outdoor mosaic where each child would create a mosaic on an 8 inch x 8 inch brick paver (paving stone), and then the mosaic pavers would be arranged together in a crazy quilt design similar to what artist Victor Kobayashi created for his mosaic patio in Honolulu.

I really like the crazy quilt approach to school projects because it allows each student to make their own art and have a real art experience instead of copying some teacher’s favorite piece of art, which usually involves more boredom or frustration than it does art. Crazy quilt projects also tend to produce more exuberant and impressive results. Copying something is merely copying something, even if that something is an acknowledged masterpiece.

Normally, school mosaic projects can use 1/2-inch or 3/4-inch sanded plywood as a backer, and the tile can be attached using a white PVA adhesive such as Weldbond, but plywood and glue are for indoors only. For outdoor and wet mosaics, you must use thinset mortar to attach the tiles to the backer, and that backer must be cement, stone or masonry. For large mosaics, a sheet of concrete backer board can be mounted to a metal wall using a frame welded from angle iron, or the mosaic can be created directly on a stone or concrete wall or a brick wall plastered smooth with thinset. In this case, the mosaic can be laid up in advance on fiberglass mesh, mosaic paper or clear mounting tape, and then these sheets can be pressed into thinset spread on the wall using a notched trowel.

This particular teacher decided to use brick pavers for her backers, but the concrete stepping stones/pavers commonly sold at building material stores could have been used in a similar way. The real issue for her project was how the students could use thinset mortar to attach each individual tile without creating a huge mess.

Thinset mortar is a sanded portland cement product with polymers added for strength and adhesive properties, so think of it as sticky concrete because that is essentially what it is. Your students might be mature and competent enough to use a bottle of glue that looks and handles just like Elmer’s glue, but how are they going to fare when they start working with sticky concrete? Now that I have your attention and your hair is standing on end, let me calm you by saying that it can be done, and it can be done fairly easily with a little forethought and planning.

One option would be to avoid setting each tile individually and lay up the designs in advance on clear mounting tape using my instructions for using contact paper and mounting tape. Then thinset could be spread on the pavers and the whole design mounted at once.

But that still involves handling thinset and some point, and sometimes you find situations where the mounting tape method isn’t practical (such as when not all of your tile have the same thickness).

Make A Prototype To Answer Basic Questions

The key too minimizing frustration and mess is to figure out your process BEFORE you involve the children, and the best way of doing that is to make a prototype in advance. In making a small mosaic beforehand, you work out the details of your materials and methods, including how the thinset will be distributed between the different children and how they will apply it to the backer.

Here are some questions you should answer by making your prototype. Please don’t let any of these alarm you because I have a practical recommendation at the end of this article that greatly simplifies everything and even eliminates some of these concerns:

How long does it take to apply tile to a mosaic of this size?

How many classroom sessions will be required?

Would it be more practical to have longer sessions instead of a larger number of short sessions?

How will thinset be applied to the stepping stones? Will the children spread the thinset themselves?

How will the children keep their hands clean while working; buckets of water and piles of rags?

How will we keep the thinset from drying out in the heated winter air or summer AC? Can we use humidifiers if necessary?

How much thinset do you need to mix up at one time? (This is answered by thinking about how many students will be working at once and how much thinset you used in one working session.)

How will we mix up the thinset? Is a parent volunteer available with a mixing paddle, drill motor and 5 gallon bucket? Do we have any parents who work as contractors and have experience with laying tile or mixing up concrete?

All of these things are relatively easy to implement, but they can make things chaotic or difficult if you don’t think about them in advance.

Thinset And Surfaces

There are a few specific concerns related to using thinset and pavers/stepping stones.

Surface Wetting

Sometimes you can drop a clump of thinset onto concrete backer board and it will harden without bonding to the backer board and it will fall right off or come off with minimal scraping. This was because the thinset didn’t really make intimate contact with the board due to surface dust. This can become more of an issue over time as you work and the thinset starts to set up as you are using it. The point is that sometimes you need to smear thinset into a surface to make sure it adequately wets the surface and makes intimate contact. Normally this happens merely by pressing a tile into the thinset, but you might do well to keep an eye out for students who are minimalists in terms of how much thinset they apply and for those who have a butterfly touch and just kind of sit the tile on top of the thinset instead of pressing it in.

Presealed Pavers

One problem you might encounter is pavers or stepping stones that have been sealed with some sort of silicon or polymer that might interfere with thinset bonding well to them. You can test for this simply by dripping some water or spittle on the paver and observing whether or not the water wets the surface. If the water wets the surface and soaks in, then there shouldn’t be any problem. If the water beads up similar to how water beads on a waxed car, or if it fails to soak in, then you know that the pavers have a heavy coat of sealant and should be avoided.

Skin Irritation

Wet concrete is mildly caustic, so it can dry and irritate the skin. A box of disposable medical examination gloves from the drug store can prevent this. You should also have the children wear safety glasses with side shields.

Overly Complex Designs And A Recommendation

Another thing you can learn from making a prototype is how much time is involved and how simple or complex the designs can be in order to be completed in the time allowed. I definitely prefer children be allowed to make original designs so that they get a real art experience, but you still need to give them recommendations about what level of detail is practical and look out for children trying to make overly complex and detailed designs. For this reason, it can be somewhat problematic for children to sketch out their designs in advance. Sometimes the mere act of drawing gets a person thinking in terms of a level of detail that isn’t practical in the medium in which the design will be executed. I have encountered this time and again while sketching out designs for my painting and mosaic.

Instead of sketching out designs, a more practical exercise might be for the students to play around with arranging tile before they decide on a finished design and definitely before they work with concrete.

I recommend making cardboard squares the same size as the mosaic backer and allowing the children to practice laying up their design on the square. If possible, give them one session to play with different arrangements and experiment with rendering different designs in the square, and a second session to finalize their design.

Then the following sessions could be about transferring the tile to the thinset on the paver. Using this approach, it would be possible for a teacher or parent volunteer to spread thinset on the pavers, and then the students merely transfer their tile designs from the cardboard squares/trays to the thinset, which would greatly minimize the amount time the children spent touching concrete.

A Practical Method For Kids And Thinset

  1. Make squares from cardboard that are the same size as the stepping stones/pavers or draw squares the size of the pavers on cardboard or trays. I prefer to cut out the cardboard squares so that they can be wrapped with contact paper with the sticky side out to prevent the tile from moving around.
  2. Have children spend one or two sessions arranging tile into designs on these squares/trays.
  3. Have teachers or parent volunteers mix up and spread thinset on the stepping stones.
  4. The children transfer their designs to the stepping stone one tile at a time. Alternatively, clear mounting tape could be used to pick up and transfer more complex designs made from smaller tile.
  5. After the thinset has hardened for a day, grout the mosaics with more thinset or grout.
  6. After the grout has hardened for at least a day or two, clean off any remaining grout residue by rubbing with a clean cloth and seal the mosaics with a tile and grout sealer.


The above instructions were written for children and beginners who just need to play around with tile to make simple designs. However, you may have more advanced students capable of making more sophisticated images from many small pieces of tile. I have written a second article Mosaic Transfer Instructions which explains how to lay up a more complicated design on a pattern and transfer it all at once to thinset or cement using mosaic mounting tape or clear packing tape.

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