How to Repaint a Metal Roof
By Clint C. Thomas, Esq. Photography By Sterling Thomas
Metal roofs seem to be in vogue today, and many people mistakenly believe that they are a product of the modern era. Metal roofs, however, pre-date the contemporary asphalt shingle roof by a couple of hundred years. In fact, I’ve been told that Thomas Jefferson’s home, Monticello, still sports its original metal roof. The types of metal roofs that are available today and those that were available during the 1800s and early 1900s have changed dramatically.
Many of us have made reference to an old farm house with a “tin” roof. Ironically, “tin” roofs are not made out of tin. Today metal roofs often consist of an alloy steel with a zinc coating applied to it for protection, known as galvanized metal. A current alternative trend in roofs is the use of aluminum. Available in a variety of color schemes, aluminum roofs require very little maintenance.
Metal roofs of all kinds have many advantages from being long-lasting to shedding water and snow quicker than an asphalt shingle roof. However, all painted metal roofs have one downside in common, and that is that they have to be repainted periodically.
Before you dive head-long into painting your metal roof you need to determine what type of metal it is, because although it may appear to be galvanized, it may in fact be what is known as terne metal. Terne roofing was made by producing the shingles or roof panels out of one of several different types of base metal and then coating the panel with a mixture of lead and tin. Terne metal has been phased out due to the public outcry about the dangers of lead, even though no specific health threat was ever discovered coming from the use of terne metal roofs.
Terne metal roofs are extremely long-lasting, but because they look very similar to galvanized metal a person can unknowingly invite problems if they use the wrong paint. Galvanized roofs require the use of a different paint than what is used on terne metal. Terne is best painted with an oil-based paint. One of my neighbors used an oil-based paint as a primer, since some of the metal was rusted, and then covered the roof with one of the specially formulated roofing paints that is sold by CalBar for use on old metal roofs for an added layer of protection. However, another neighbor did like myself and only used an oil-based paint. Galvanized steel, on-the-other-hand, cannot be painted with an oil-based or aluminum-based paint. Galvanized metal requires either a zinc-dust type paint or a latex paint.
My house was built circa 1880 and still has its original terne metal roof, which consists of individual metal shingles with an embossed decorative pattern. After many years of exposure to the elements, the paint on the roof began to wear off, crack and peel, necessitating a new paint job.