Coatings Project Brings a New Look to an Old Observatory
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Coatings Project Brings a New Look to an Old Observatory |
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On a clear night, the view from the David Dunlap Observatory at the
University of Toronto can reveal the deepest secrets of the universe
to the captivated students and scientists within. Today, the observatory houses the second largest telescope in North America. But the facility has been serving as a launching pad for boundless flights of imagination since its construction in the 1920s, leading to the university's world-renowned excellence in the field of astronomy. From the surrounding landscape, however, the greater concern for the university was not the view from the observatory, but the view of it. Located on a rise in the Richmond Hill suburb of Toronto, the observatory is visible from major highways. And that meant passersby could easily see that by the late 1990s, paint was peeling off the landmark structure in sheets. While the observatory continued to provide wondrous sights to those on the inside, on the outside, it was viewed as an eyesore. For David Wood, a maintenance engineer with the university, the solution was simple: the observatory would be painted. "We conduct a lot of business through that facility," says Wood. "So it was a matter of aesthetics. The university has a standard of appearance that must be maintained." But as Wood well knew, maintaining that appearance would prove to be a complicated matter. COATED COPPER The upper dome portion of the observatory, which rotates open to allow the telescope a clear view of the sky, is made up of copper panels measuring roughly 2-by-2 feet and covering a total of about 8,000 square feet. The copper offered an attractive appearance when it first topped the structure, and the light-reflective material had functional value as well. Optical technology at this level requires a polished telescope lens more than 6 feet in diameter. A sudden change in temperature could cause condensation to occur on the lens, and even in microscopic amounts, that condensation could ruin a night's stargazing. However, the shiny, metallic surface provided by the copper reflected heat away naturally. The interior of the dome has always been unheated, and as a result, the copper finish would ensure that temperatures would be equalized inside and out every time the dome was opened. Or so the designers thought. Only a few years after construction, the copper began oxidizing and turning the surface to a dull green color that no longer reflected heat -- in fact, it absorbed heat. Copper is a substrate not normally covered by coatings of any kind, but the situation demanded either a regular dose of costly copper cleaning, or a new finish. So the copper dome was given its first coat of paint in the 1940s. Coatings technology then lagged far behind the standards of today, but the designers were able to locate a titanium- based paint with outstanding light reflective qualities, thus returning the heat reflective characteristics the dome requires. Over the decades, a full re-coat project was never again attempted. The original coat held up reasonably well but deteriorated with age. Household exterior paints were used to either touchup or recover the old finish every 15 years or so, but by 1998, Wood was ready for a more lasting measure. He called in Dan Orrett of Harrison-Muir Painting for an assessment, and Orrett called on Sherwin-Williams Corrosion Specification Specialist Rick Williams and Industrial Marine rep Jerry Golshesky to come out and take a look with him. "When we arrived, the copper was showing through on about 30 percent of the dome, but on other parts there were more than 20 mils of paint," says Orrett. "In short, it was a mess of blistering paint." LOW BID Being a public entity, the university was required to seek bids on the project, and Harrison-Muir came in with the lowest bid. But based on his earlier assessments, Orrett knew going in that this would be a tricky project. Removing the old finish would be the first challenge. "We couldn't sandblast with that telescope there," says Orrett. "That was absolutely a no-go from the university's standpoint, and that's very understandable." A Harrison-Muir sister company is Aquablast, and as the name suggests, the firm's specialty is high pressure water blasting. The technique, high pressure water at 30,000 psi, would prove to be the most efficient means of removing the layered coatings on the dome. |
Several issues arose. First, protection of the equipment inside was
crucial, so the interior of the dome was sealed completely to ensure
no water would enter. But it was just as important that the job be
kept tidy on the outside for environmental as well as public relations
reasons. To that end, Harrison-Muir crews built a moat around the
base of the observatory, raising walls with flexible poly pipe, over
which a tarp was laid to contain the water. From there, the water
ran into a 1,000-gallon settling tank, then through a 25-micron filter
before running into a second settling tank. After filtering through
a 5-micron filter, the water was ready to be reused. While that plan proved a success, Orrett said the Aquablast crews still had to work delicately during the project. "Copper is very malleable," says Orrett. "They just really had to take it easy with the water and be very careful not to damage the copper. You couldn't treat it like it was galvanized steel." PRIME COAT The removal was completed in eight days by a crew of two. Then Harrison-Muir painters stepped in to apply the coating system. First was a sprayed single coat of Sherwin-Williams DTM Wash primer at 0.7 to 1.3 mils dft. The finish consisted of two roller-applied coats of Acrolon Polyurethane at 1.5 to 2.5 mils dft. Gloss was an issue due to the reflectivity concerns, and after consulting with Wood, Williams and Golschesky, Harrison-Muir applied a slightly lower gloss finish than they had speced. The finish still met the reflectivity levels necessary, and did a better job of hiding surface irregularities. The finish coat was completed within one month of the start of the water blasting. "We ended up with one, simply a more attractive sheen finish on the dome, and two, higher reflectivity to help keep the telescope in a proper working environment," says Wood. "And every time it rains, any accumulated dirt is being washed right off it, so it always looks fresh and clean. That wasn't happening before." 
PART TWO The completion of the dome, however, marked only half the completion of the project. The galvanized steel sides of the observatory were also bid to be recoated the following summer of 1999, and Harrison-Muir again came in with the lowest bid. This base, with a surface of some 8,000 square feet, bore several recoats accumulating up to 35 mils of various paints, including a cementitious layer apparently applied to smooth the finish some years ago. But by last summer, it all added up to a "weird finish," according to Orrett. These surfaces were also water blasted with the same recycling and containment systems used the year before. Then a light prime coat of Sherwin-Williams DTM Wash Primer was applied at 0.2 to 0.4 mils dft, followed by an intermediate coat of DuraPlate 235 at 3 to 5 mils. One coat of Acrolon Polyurethane at 2 to 3 mils dft made up the finish coat. The final two coats were roller applied to ensure no overspray occurred. Finally, the last phase of the job was the ladders, catwalk and rails that surround the observatory. Due to budget constraints, the university had to cancel its hopes for a full dip-removal plan for the prior finishes, but Harrison-Muir had an alternate plan and a coating system that met both their needs and their budget. They prepped the surface with power tools instead, then applied a prime coat of DuraPlate 235 at 4 to 6 mils dft, followed by a finish coat of Acrolon Polyurethane at 2 to 3 mils dft. "Our proposal was for 80 percent removal of the old finish, but having a coating system that still functioned well with less surface prep gives us an advantage," says Orrett. "It's a good protection system, and it allowed the university to stay within their budget." For Wood, the finished product is his biggest concern. After all, he and many others look at the observatory far more than they look through the telescope housed inside. "There's a tremendous difference in appearance," he says. "We're very happy with the final product." "It's a good protection system, and it allowed the university to stay within their budget..." |
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