All matter expands or contracts with temperature changes. A simple instance of this is the common thermostat which is composed of two dissimilar metals. Various building materials used in modern construction likewise expand and contract at different rates. It follows, therefore, that unless provisions are made to counteract this thermal movement, joints will open and cracks will develop, thus permitting moisture to start its destructive action. Water is one of the most powerful solvents, especially when it freezes and thaws. When its temperature drops from 35 degrees F to 28 degrees F, it expands nearly 10 percent in volume; pressures up to 10,000 psi are generated and thus water saturated concrete will crack, spall and deteriorate rapidly under such forces. Moisture enters the structure, and causes costly interior plaster and paint failures to occur. In view of the above, the designer, plant engineer or specifier must give due consideration to the coefficient of thermal movement of each building material anticipated for use in the particular type of building on which he is working. The proper balancing of building materials and consideration of their limitations will produce sound, durable and comparatively maintenance free structures.