When architects design with brick, light or dark earth tones don't have to be their only color options. Calcium silicate bricks have a natural near-white color, with a yellow, gray, or pink tint, depending on the color of the sand used to make them. With pigments, they can be made in light pastel colors, even greens and blues. If the architect desires, the bricks can be made with a second color streaked through them. Or they can be dipped in acid after hardening to intensify their color. WHAT IS CALCIUM SILICATE BRICK? Calcium silicate masonry units are made from sand or other siliceous material and a little lime. The moistened mixture is pressed in a mold by a special hydraulic press, then cured in a steam-heated autoclave at 400 degrees Fahrenheit for up to 8 hours. In the autoclave, the lime reacts chemically with the silica to form hydrated calcium silicate, a powerful, durable cementing agent that binds the sand particles. MANY SHAPES, TEXTURES, AND SIZES In addition to its many colors, this brick can be pressed into a variety of shapes, including interlocking tongue and groove units, single and double bullnose, chamfers, and squint styles. Their surfaces usually are uniform and smooth. Texture is obtained by sandblasting, mechanical brushing, or adding flint aggregates to the mix. STRONG AND DURABLE In the United States, calcium silicate brick must meet ASTM C 73. Cycles of wetting and drying and repeated freezing and thawing have little effect on this brick. Efflorescence is not a problem either because the raw materials don't carry soluble sulfates or other salts.