Glass Mosaic Tile Art – What Exactly is Grout?

Making wonderful glass mosaic tile art is easy! Let me show you how.

Ever wonder what grout actually is? As a mosaic artist, you should. Yes, it's cement, but what's cement? Even if you could not care less, as a mosaic artist, you should understand the materials used in your work. So, let's discover just exactly what cement is.

Portland cement is the most common type of cement. Did you know that Portland cement is a generic type of cement, not a trade name? Many different cement companies make Portland cement. Joseph Aspdin, a bricklayer in England, invented and patented Portland cement in 1824. He named it "Portland" cement because it resembled the limestone from the Isle of Portland (a 4.5-mile long by 1.5-mile wide limestone peninsula extending into the English Channel). He heated a coarse mixture of crushed limestone and clay in his kitchen stove. The resulting concoction hardened after he added water.

Although it may contain small amounts of various elements, cement comprises four basic components: calcium, silicon, aluminum, and iron. These elements are commonly found in limestone (source of calcium), clay, and sand (sources of silica, aluminum, and iron). Raw chunks of these ingredients are crushed and measured to get the correct mixture (limestone is by far the main ingredient). The crushed materials are then heated to more than 2500 degrees F (that's hot!). The extreme heat causes a chemical reaction and turns the materials into calcium silicates. The resulting material is called "clinker." The clinker is then cooled, crushed, and manufactured into a fine powder. The gray powder that we know as Portland cement is so fine that one pound of cement contains more than 100 billion grains, which is fine enough to pass through a sieve that can hold water. That's right! Finished Portland cement can pass through an extremely fine sieve but water can not. Is not that amazing? So, now that we know what cement actually is, the next question is why and how does it harden when water is applied?

Cement hardens because of "hydration," a chemical reaction caused by water resulting in a new compound. The reaction forms chemical bonds with water molecules that are called "hydrates." The calcium silicates react to release calcium and hydroxide ions. When the reaction process saturates the material, the calcium hydroxide crystallizes. At the same time, calcium silicate hydrate forms. As time proceeds, the calcium silicate hydrate grows (ie, the cement hardens) and the process continues until there are no more water molecules and un hydrated compounds. The resulting substance is rock-hard cement.

Grout adds strength to your mosaic, keeps out dirt, and helps protect your mosaic, especially outdoor projects. Grout is not an adhesive, so do not try to adhere tesserae to the mosaic's foundation using grout.

Remember, making mosaic art is easy. You can do it. Yes, you can!