Coating removal products are not the only consideration for odor and impact on occupants; coatings also can have strong fumes, and application should be tested during low-occupancy hours, such as evenings and weekends. Adhesion testing, by means of peel tests and other methods, may be used to evaluate and confirm the bond between coating and substrate, as well as ease of removal and reapplication.
Once testing has been completed and the substrate prepared, the coating should be applied in overlapping segments, incorporating reinforcement, such as fiber mesh, as appropriate. Coating thickness, typically measured in mils of dry film thickness (dft), should comply with manufacturer requirements and be verified in the field. Manufacturers often supply measurement tools for this purpose.
Too thin, and the coating will provide inadequate and/or uneven coverage; too thick, and the coating is unlikely to fully cure and may be vulnerable to tears and gouges. Additionally, if not fully cured, the coating may fail to adhere completely to the substrate, leading to peeling, blistering, and other manifestations of premature breakdown.
At termination points, the design professional should provide design details for coating finishing, such as feathering onto adjacent surfaces or application of protective masking on surrounding finishes to shield against accidental—and potentially irreversible—drips or splashes.
Once application is complete, the area should be protected during curing to provide favorable ambient conditions and create an atmosphere conducive to thorough drying and optimal adhesion. Project sequencing should aim to protect freshly coated areas from adjacent dust-producing operations.
A pragmatic approach
Unless the cleaning and removal of existing coatings and the specification and application of new coatings is guided by a knowledge of material properties and appropriate techniques, permanent damage to the building may be the unintended result. Before applying a water-repellent or waterproof coating, underlying problems that could be the cause of water infiltration should be addressed, and serious consideration given to whether the coating is necessary. For historic restoration, including buildings of the Modernist era, the composition and appearance of the original paint should be closely replicated to protect the period character of the structure.
In all cases, coating selection should be guided by a long-term view of cost implications, rather than an up-front cost comparison of available products. The expense of rehabilitating an ill-conceived or poorly executed coating project can far outweigh the cost of appropriately specified, designed, and applied paints and coatings suitable for the substrate, condition, and location. Moreover, once a coating has been applied, it must be maintained, so the long-term cost of cleaning, upkeep, and eventual re-coating must be taken into consideration.
With a long history in building construction, paints and coatings are a vital and often little-considered element of the building envelope. Through thoughtful planning, research, and design, the prudent building owner or manager can enjoy the protective and aesthetic benefits that the judicious use of coatings can impart to the building exterior.
|ENVIRONMENTAL CONSIDERATIONS FOR COATING SPECIFICATION|
With the rapid growth of the petrochemical industry after World War II, most standard paints and coatings began to incorporate materials derived from petroleum, which, when refined from crude oil, contains hydrogen and carbon molecules that form the long-chain macromolecules in plastics and synthetic resins. A non-renewable resource, petroleum contributes to air and water pollution as part of the extraction and refining process. As an alternative, paints and coatings manufactured from plant sources and minerals are available. Federal procurement requirements for government projects encourage the specification of biobased paints and coatings, as opposed to those from non-renewable resources like petroleum.
Alternatives that are low-toxicity and low in volatile organic compounds (VOCs) exist for most conventional paint and coating products. However, there is no standard regulatory definition for ‘low-VOC’ or ‘low-toxicity,’ and products labeled as such can still contain harmful or odorous ingredients, including ammonia, formaldehyde, odor-masking agents, and fungicides and bactericides. Water-based paints are usually safer to handle than those with organic solvents, and they can be cleaned up with water, reducing health risks to workers and occupants and minimizing (or eliminating) hazardous waste.
While the performance of biobased and low-VOC products has improved over the past several years, design professionals and building owners should consider product performance data and test results when selecting any type of paint or coating, including newer environmentally conscious products. The right coating combines ecological sensitivity with performance characteristics suitable for the substrate, building, and situation.
Elizabeth A. Hnatiw, AIA, LEED AP BD+C, is project architect at the Washington, D.C., area office of Hoffmann Architects Inc., an architecture and engineering firm specializing in the rehabilitation of building exteriors. With a background in material science and historic preservation, Hnatiw has expertise in the evaluation, specification, and design of coating systems as part of comprehensive building envelope rehabilitation. She may be reached at firstname.lastname@example.org.