Mosaic grout is a concrete-like substance used to fill spaces between mosaic tiles. The purpose of the grout is to strengthen the mosaic item by filling in the gaps between the tiles, essentially making several small pieces one larger, stronger piece. By filling in the gaps between the pieces, the grout also functions to level the surface of the mosaic tiles. In addition to its utilitarian roles, mosaic grout is also available in a variety of aesthetically pleasing colors that can be used to accent mosaic tiles and put a finishing touch on a mosaic creation.
For convenience in handling and transporting the product, most mosaic grout is sold in a powder form. The powder is then dumped into a container, and water is stirred into the powder until it reaches a desired consistency. Depending on the artist and the project, a thicker or thinner mixture may be preferred. Mosaic tiles placed very close together may need a thinner mixture. A project that needs to be grouted on a vertical slope or incline, such as a wall or ceiling, may benefit from a thicker mixture that will stay in place better than a soupier concoction.
The type of water mixed with grout varies among artists and manufacturer's instructions. While some mosaic artists often use tap water straight from the faucet, others will only use bottled or distilled water. The main reason for the water debate is the thought that iron and minerals in tap water can discolor or stain the mosaic grout. Another option is to purchase ready-made grout, which is already in a liquid form. While it is still moist, spilled and excess grout can typically be cleaned up with a water and a sponge.
There are two basic types of grout: sanded and sandless. Sanded grout is used for filling larger spaces between tiles as the sand provides added strength. The sandless grout is the preferred choice for tiles that are spaced very close together, such as those spaced 1/8 inch (3.2mm) or less. The sandless grout can better seep into these small spaces and crevices. It also offers an advantage when the mosaic tiles are fragile or painted, such as vintage china pieces. The sanded ground will actually act like a sandpaper as it is wiped off the project and can scratch delicate tiles; however, the sandless grout is less abrasive and reduces the chance for this type of damage.
Another option when choosing mosaic grout is the color. Many mosaic projects feature a white or light gray grout, but a wide array of colors are available to bring out the colors in the tiles, including terracotta red, blue and mauve. In addition to purchasing premixed grout colors, artists can also make custom-mixed grout colors using colored powder. Due to the complexity of mixing and matching colors, it is recommended to mix enough of any one color to complete an entire project rather than mixing several small batches. After the grout is applied to a mosaic project, it is typically left to air-dry before being sealed or used.