The cost for metalizing varies with the project. In general, an owner can expect to pay about 30-40% more for a metalized coating than for painting. To illustrate the life cycle cost of a protective coating, we provide the following example.
Some structure owners are convinced that painting is inexpensive and that paints will work as promised. But does painting consistently provide a 20-year service life as often claimed? Is the structure owner "misled" by test results that are not supported by experience? We draw your attention to the September 1998 issue of the "Journal of Protective Linings and Coatings" and there to an article entitled "New Coating Test Method". This article describes a new ASTM accelerated test method for evaluating paint life. Apparently there is some doubt as to whether or not the current accelerated ASTM test method accurately reflects performance. One should consider the problems associated with zinc-rich and other paints. Two additional articles in JPCL that should be read are "Trouble with Zinc-Rich Primers, Parts 1 & 2", appearing in the August and September 1998 issues of the magazine. These articles describe in some detail the practical problems associated with the transportation, storage and application of these highly touted paints. It may be that painting is more problematic than metalizing.
A coating's effectiveness is measured over time. Do not mistake claims about newly formulated VOC compliant paints for performance. Ask for examples of where a newly formulated paint has worked for 20 years or longer. On the other hand, metalizing has been used successfully for more than half a century.
A new steel bridge with a surface area of 25,000 ft2 is coated in shop by painting or metalizing. The metalizing system consists of .006"--.008" of sealed aluminum or zinc. The paint system consists of a zinc-rich primer followed by an intermediate epoxy and a urethane topcoat. We expect to repaint at 25 years and again 15 years later. We expect to do a modest amount of maintenance on the metalized coating at those same intervals.
The installed cost for metalizing will certainly be higher than for painting. However, the 50-year cost per square foot per year for metalizing is less than half that of the painting! In our opinion, the present value cost for metalizing will be about $.17/ft2/year and the present value cost for painting will be about $.36/ft2/year. In determining these estimates, future maintenance costs were inflated and discounted to today's dollars. Remember, it is understood that when the owner decides to paint, the total cost, the initial cost plus all maintenance re-painting costs over the structure's service life, is accepted by the owner.
In order to eventually control maintenance coating and re-coating cost, the longest maintenance interval and the lowest life cycle cost (LCC) materials and processes must be used otherwise the maintenance coating deficit will continue to grow. Most owners have always accepted that life cycle costs of metalizing are less than for painting but were put off by initial costs which were 2-3 times higher. Now that high capacity arc-spray guns are replacing old flame spray technology, the initial cost premium for metalizing is less than 40% for many applications and old cost assumptions must be revisited.
For more information on the evaluation of life cycle cost, we again suggest reading the Federal Highway Administration's Report FHWA-RD-96-058 "Environmentally Acceptable Materials for the Corrosion Protection of Steel Bridges".
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Joseph T. Butler, Inc.
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