Outdoor Mosaic Project

An example of how to design, tile and grout an outdoor mosaic on a cement backer.

The following is a case study of an outdoor mosaic by David Cater, using work-in-progress photos taken by the artist. We have a separate page which summarizes our general instructions for outdoor mosaics, but the example below gives lots of insight.

I was deeply touched by David’s project, especially how he hand set each tile. My first mosaic was made almost in a trance state where I had no concern for efficiency or how much work it took. I hand chipped broken china with an ordinary claw hammer and didn’t even take the time to get a tile nipper, even though that tool would have save me hours and hours. It really was a labor of love, and I see that in David’s project too.

In the text below, I explain how David executed his project, but I also make comments on how the mosaic could have been made with less labor.

Concept Sketch

Like most mosaic projects, David’s sidewalk mosaic started as a concept sketch where the street number of his house is incorporated with a cardinal and dogwood design. Note how the red cardinal matches the red of the border, which helps to integrate the picture with the design as a whole. Note how the blue sky and the white dogwood make good contrasts with the red.

Choosing Colors

Color choices are as important as the composition. To save frustration, get your color choices worked out before you attach the first tile. Sometimes it helps just to play with tile laid out on the surface to be mosaiced. I like to draw my cartoon (outline) on the surface and lay the tile in the different areas of the cartoon.

Design tools like color wheels are great for picking out initial choices, but colors usually have to be laid side by side before you can be absolutely certain they work together. This is particularly true when using different shades of each color

Initial Layout

David laid out his design on a sheet of plywood as a temporary surface. Note that David screwed a frame around his work area to define the size of the mosaic and provide a stop for straight edges.

To speed the placement of tile, an outline of the design could have been sketched onto the plywood. Most people have difficulty doing this because they aren’t experienced with drawing. The good news is that you don’t have to be.

Easy Method to Transfer and Enlarge Drawings

Simply use a ruler to draw a grid on your sketch. Then draw another grid on your larger surface. Notice that each square of the grid on the drawing contains just a little part of the drawing, usually just a few curved lines. Draw these same curved lines in same square of the large grid. You don’t even have to think about what you are drawing. Just copy what’s in each square, one square at a time. This makes it easy to enlarge and transfer outlines.

Complete Layout

In the above photo, we see that David has his design completely laid out and all tiles positioned, which represents many hours of labor.

At this point, clear contact paper could have been pressed onto the face of the tile to pick the entire mosaic up at once, which would allow the mosaic to be installed rapidly by pressing into thinset mortar. However, one problem with using clear contact paper to pick a mosaic up like this is that individual tile can get out of position while the contact paper is being pressed down. This problem can be minimized by laying out the tile on a nonslip surface, such as a sheet of rubber. That way the tiles can’t easily slip out of place when the contact paper is applied.

Another labor-saving method would have been to lay the mosaic out upside down on brown mosaic paper such as the kind we sell. In that method, the tiles are temporarily glued face-down on paper using a water-soluable glue like Elmer’s Glue. The sheet of mosaic is then pressed into cement, which allowed to harden over night. Then the paper is misted with water and peeled off.

Surface Preparation

David poured some new concrete approximately 4 inches thick for his mosaic. Note that the concrete is slightly lower than the surrounding brick so that the surface of the mosaic will be flush with the brick. You can put mosaics on existing cement, but you should use a wire brush to scour the surface to remove any loose sediments and invisible sealers, which could interfere with bonding.

Mounting Mosaic Tile

David manually transferred each tile from his temporary tray and mounted the individual tile using thinset mortar.

Note that this means David had to manually position each tile twice: once in the tray when he laid up his design and then once again when he sets each individual tile in mortar. That is why using contact paper or mosaic mounting paper to pick the entire mosaic up at once for rapid installation saves an enormous amount of work.

Another technique for speeding the work is to lay the mosaic up on 1/2″ concrete backer board and then cement the entire concrete board in place using thinset mortar. The only caveat would be to make sure the edges of the board aren’t damaged and crumbly. The edges of concrete backer board can be repaired and reinforced using thinset mortar.

Grouting the Mosaic

Grouting is done by smearing grout across the face of the mosaic and pressing the grout into the gaps between the tile. Indoor mosaics do not require grouting and the tile can be pressed tightly together. Outdoor mosaics must be grouted because the grout keeps water from penetrating between the tile, which is disastrous especially when the water freezes.

Make sure that you press the grout between the tile very thoroughly so that there are no voids or bubbles beneath a thin veneer of grout. This takes some repeated rubbing and pressing on the tile, and this is why you should never grout before the cement or adhesive has been allowed to harden for several days.

Note that a thin haze of grout can be buffed off after the grout has hardened, but most of this excess grout should be removed while still wet. The mosaic in the photo still needs some wiping. Make sure your sponge is damp but not so wet that drops of water could squeeze out and damage the wet grout. Keep your mosaic covered with plastic as it cures or otherwise keep it from drying out. Otherwise the grout will be soft and crumbly. Remember grout and concrete harden by binding water, not by dehydration.

Seal Thoroughly

I should also note that outdoor mosaics on horizontal surfaces are particularly vulnerable to moisture and freeze damage because horizontal surfaces allow water to pool. (Keep in mind that the mosaics of the ancient Greeks and Romans lasted for millennia because the Mediterranean is a warm dry climate.) One thing that can be done to minimize this risk is to slightly tilt the otherwise flat surface or to make it slightly round. For example, the seat of a concrete bench can be rounded slightly using a small amount of concrete mortar to build up the center of the seat by approximately 1/2″ and gently sloping down to the edges. Of course, this would need to be done at least a few days before attaching tile.

Regardless of the orientation, all outdoor mosaics should be sealed thoroughly with a tile and grout sealer, taking special care to seal the edges. Multiple applications should be made to ensure that all of the tiny pores in the grout and concrete are sealed. For added strength and stain resistance, you can use a concrete sealer instead of an ordinary tile and grout sealer. Again, the most important points are to take special care to seal the edges and use multiple coats to ensure complete coverage.