by Martin Holladay Aluminum coil stock, which has been used for years to cover trim on re-siding jobs, is becoming standard on new homes, too Ñ part of the trend toward low-maintenance exteriors. Manufacturers of aluminum trim coil offer two types of finish: smooth and striated. Smooth trim coil, which has been on the market the longest, is a thin aluminum flashing finished with polyester or acrylic paint. Striated coil has a textured finish, providing a better visual match to vinyl siding. Some manufacturers refer to striated coil as PVC-coated coil. Jerry McKie, national sales and marketing manager at First American Coil, notes that striated trim coil, like smooth coil, is basically painted aluminum. "All it is, is paint," says McKie. "It's paint with vinyl chloride in it." The PVC paint used for striated coil is thicker than the paint used for smooth coil. The dry film thickness of the paint on striated coil measures about 3.5 mils, compared to the 1-mil paint film on smooth coil. Because the PVC coating is applied so thickly, it forms striation patterns as it dries. "The striations depend on the speed of the roller as well as the properties of the paint," says Dan Hawk, metal products manager at Alcoa. From a distance, the striations look a little bit like wood grain.

In the U.S., the gauge of almost all aluminum trim coil sold, whether smooth or striated, is nominal 0.019 inch. Many people in the coil industry acknowledge that actual measurements of aluminum coil products are often less than their nominal sizes. "The coil is referred to as nominal .019 inch, but most of the time it is thinner,"...

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