Installing Tiles in Concrete
Most tile installations are straightforward and simple, but not all tiles are square, not all are installed according to rigid lines, and not all are suited for exterior applications. The tiles featured here have a tough, durable glaze over an impervious porcelain bisque, can stand up to heavy foot traffic, and may be used in freeze/thaw applications. Although tiles normally cover an entire surface, here they are used individually, to accent an otherwise plain concrete walkway. As long as the tiling and concrete materials are specified and installed properly, the technique of embedding tiles in concrete can be used on most interior or exterior slabs and walkways. Only impervious tiles should be used in freezing conditions (impervious tiles absorb less than .5% moisture).
A wide range of materials can be installed using this technique: ceramic or stone tiles and shards; brass, cast iron or stainless steel castings and forgings; seashells; beach glass - practically any material whose wear and absorption properties are similar to non-vitreous or impervious paver or floor tiles. As with conventional ceramic tiles in functional, wet-area installations, alternative tiles in similar applications need to be grouted. In the following technique, the concrete is the grout, and it needs to surround 100% of each tile for the best results and easiest maintenance.
Some tiling materials can stain the color of the grout (with white grout, some designers may encourage the appearance of the bright blue stain caused by the oxidation of brass or copper objects). Cast iron and steel may produce orange or brown oxidation stains. With concrete, staining can still occur, but the colors will be muted. If staining is going to be a problem, any metals used for tiling should be stainless steel.
The ProcessThe basics of the technique involve wiggling the tile or other object into a soft, previously leveled bed of concrete; floating the displaced concrete paste into any voids surrounding the tile; allowing the matrix to set and begin to harden; and finally, cleaning the surface of the tile (Note: some experienced concrete finishers may prefer to position the tiles as they are screeding and floating the soft concrete).
Timing is critical. The technique works best when the concrete has begun to setup, but is still soft and plastic. This consistency allows the relatively hard body of the tile to displace the stones in the concrete. If the concrete has set too much, stones in the way of the tile will have to be dug out, and the back of the tiles will need to be covered with a layer of an adhesive mortar, e.g. medium-bed thinset mortar. Depending on the ambient temperature and the type of concrete, placement of the tiles on some installations can begin in as little as five minutes after the slab or walkway has been screeded and floated smooth. As the temperature drops, concrete takes longer to set firm (for best results, materials containing Portland cement should only be used when the temperature is between 55 and 90 F). This technique does not require adhesive, but for best results and maximum adhesion, a thin (1/16-inch) scratch coat of latex thinset mortar on the back of each tile is recommended.
Next, use a wood, steel, or rubber float to press the tile level with the surface of the concrete (photo 2). If the tile sits below the surface of the concrete, remove the tile, back-fill its void with additional concrete paste, replace the tile, and re-float the entire surface as needed. During this process, voids may develop around the tiles. Pack these voids completely with concrete paste (photo 3).
After the concrete goes from plastic to firm, the surface of the tiles can be cleaned. To do this, use a barely damp sponge, and avoid disturbing the surrounding concrete (photo 4). If the surface of the walkway or slab is to be exposed aggregate, the tiles or other embedded objects may be cleaned during that operation. Within an hour of finishing, remove all cement haze from the surface of the tiles with a soft cloth. Avoid acid cleaning unless approved by the tile manufacturer.
Damp curing of the concrete walkway or slab is recommended, even if the concrete is mixed with a latex or acrylic additive. At the very least, the concrete should be protected from contact with direct sunlight, which can dry out the concrete prematurely, interrupt the curing, and ruin the concrete.
Tiles supplied by Michelle Griffoul Studios.