These rock hard, durable tiles are made from a centuries old process. These tiles are made from marble and Portland cement and natural mineral pigments. The tiles are made in three layers which undergo intense pressure from a mechanical hydraulic press. Our tile are not fired. The pressed tiles are soaked and cure naturally like structural concrete. Each tile is hand made individually and is a work of art. There will always be slight subtle variations in each tile and that is a part of the charm.
Before any cement tiles can be made, you need molds. A shape mold, sometimes called a "frame" is required to hold the shape of the tile. These usually come in three to four pieces. Cement tiles are build up-side-down, so the base plate of the mold will contact the surface layer of the new tile. These are usually polished flat, but some are given relief patterns, to form textured tiles for better slip prevention on sidewalks, and other uses as outdoor pavers. A frame attaches to the base to shape the sides. These are often made in two pieces that clamp together against the base. A top piece sometimes called a "cork" acts as a cap after the tile is assembled to evenly distribute the pressure of the hydraulic press.
A Cement Tile Pattern Mold
The magic of making encaustic cement tiles comes from the hand-crafted pattern mold that is used to form the colorful design in the tile. Similar to an elaborate cookie-cutter, the pattern grid has different sections into which the colorful mixes are poured. This pattern grid is securely set into a mold framework that defines the boundaries of the tile. While a tile-maker may have very few shape molds... perhaps one 8"x8" frame per workstation, and even fewer of the other shapes, each shop will have hundreds and perhaps a thousand or more pattern molds. Most shops will have at least one full-time artisan devoted to crafting pattern molds.
Creating the color slurries requires more skill and artistry than perhaps anyone else in the shop, rivaled only by the mold-maker. The pigmented surface layer begins as a very wet concrete slurry. Exact formulas are often family secrets. This layer uses white Portland cement, rather than the standard gray cement used in the tile body. The sand used as an aggregate is also the finest in the tile. Coarser aggregates are used in the deeper layers. The slurry is pigmented with natural mineral pigments such as iron, cobalt and chromium oxides. To add a little more difficulty, the color will change slightly as the cement cures, and will be affected again when sealed. This is the reason we always seal our sample tiles, to provide our clients with the best representation of their finished installation.
Once the station is prepared with the needed materials, tile production begins. The base of the mold is oiled (for a clean release, and a better surface texture), the frame assembled, and the pattern mold is inserted. The artisan carefully pours the appropriate color slurry into each region.
I have seen three distinct styles at this stage. Shown in the video is a tool that can best be described as a stoppered funnel. The color slurry is held in the funnel, with a rod holding a stopper. As the artisan positions the funnel over a color region, he lifts the stopper-rod long enough to release the correct amount of pigmented cement. Another very common tool resembles a cross between a garden trowel and a gravy boat, with a deep trough and a very narrow pour spout. Finally I have also seen implements that resemble cooking ladles, with the handle extending straight out from the cupped end.
When all of the regions are poured, the mold is shaken, twisted, vibrated, or pounded to help distribute the color and allow potential air bubbles to work themselves out. The pattern mold is then lifted out of the frame for the next step.
Depending on who you ask, cement tiles can have two or three layers. We tend to refer to only two: the color layer and the tile body, but production does require three different formulas.
After the pattern mold is removed, a very fine mix of sand and cement are added to the mold with a sifter. When pressed, much of the moisture from the color layer will be pushed up into this layer, drying the color layer enough to hold a solid shape. This layer is applied very carefully, so that the color layer is not disturbed.
Next, the remainder of the body material is added, often by hand. This will include the same basic components for concrete, with much coarser aggregate than the surface and intermediate forumlas. This layer provides strength, and should have a course texture to help the thinset mortar adhere to the tile during installation.
At every step of the process, the tile maker can be seen cleaning excess, and working towards a consistent density and level. You may notice some slight packing along the edges and corners. This helps produce sharper, more resilient edges in the finished tile.
After the tile is constructed and the frame is capped by the cork, it is compacted by a hydraulic press. The pressure drives out air, and equalizes the moisture from the color layer. The compacted tile will be solid enough for gentle handling.
The tile is removed from the mold. First the pressure of the clamps of the frame are released, allowing the tile maker to lift the frame away from the sandwich of tile and steel. The pressure of the cork helps prevent any of the material on the edges from lifting away from the tile. The cork is removed, and then the tile is carefully separated from the base, and placed on a rack.
Good tile makers are very fastidious, and remind me of good interior painters. Tile makers often have smudges of cement and marble dust on their shirts and aprons by the end of the day, but they are constantly brushing and cleaning their molds and workstations. At each stage they collect excesses, to make their way into the next tile with as little waste as possible.
The completed tiles now only lack moisture and time. Concrete is a mixture of cement, aggregate (sand, gravel, etc), and water. Cement tiles may use more precisely controlled ingredients than structural concrete, but the basic process is the same. Cement cures and hardens chemically over time. It is not that the cement dries, but that it goes through hydration and carbonation, chemical reactions that converts the calcium oxide in the Portland cement to calcium hydroxide, and eventually calcium carbonate.
After pressing, encaustic cement tiles are soaked in water to ensure propper hydration for curing. It takes about 4 weeks for the cement to reach 90% of its potential strength, and it will continue to gain strength for decades.