How architects can avoid failures when specifying coatings
The success of paints and coatings begins at the specification stage
AIA Partner Behr Paint Company provides best practices for specification writing.
One of the roles of an architect or designer is to specify the color scheme. But some designers confine themselves to just that—color. However, selecting the right coating is just as important as choosing color. It is also important for architects and designers to understand not only the coatings involved in the project specifications, but also the characteristics of the various substrates so they are factored into the specification writing process.
Causes of coating issues
Coating issues occur when the coating deviates from its intended purpose and use, which is to protect the underlying substrate and provide aesthetic appeal. In some cases, issues can also arise from failure to follow the manufacturer’s label instructions and recommendations. The manifestation of coating issues is often slow but progresses rapidly when not addressed promptly.
Coating issues come in various forms, but the most common ones are:
- Peeling: An adhesion failure whereby the paint film pulls away from the surface. There are two types of peeling, film failure (the coating is peeling down to the bare substrate) and inter-coat failure (one or more coats separate from a previous coat). Most peeling is a result of inadequate surface preparation or failure to apply coating under proper environmental conditions.
- Fading: The gradual loss of color of one or more pigment(s) resulting in the lightening of the coating film. It often starts as chalking, then fading eventually occurs. This problem is prevalent on dark colors since these tend to absorb more heat than lighter ones. It may also be common in coastal areas as the salt air and atmospheric moisture conditions cause a corrosive environment that speeds up the fading of the coating.
- Blistering: This occurs when the coating film lifts from the underlying surface, forming bubbles. This is usually caused by heat, moisture, or a combination of both. This condition may eventually lead to peeling.
How to avoid coating issues
Preventing future coating issues starts at the specification stage. First and foremost, ensure the specification is current and tailored to suit the project requirements.
Follow these guidelines when writing specifications:
- Use simple, clear language without jargon to minimize misinterpretation; avoid using legalese and scientific jargon as well as restricting vocabulary to words in common usage. Avoid using alternatives (e.g., “degloss” for “sand”) just to make the text more interesting. Words should be selected to ensure that their meaning is clear and unambiguous, while phrasing should be brief and expressed in the imperative, i.e., “must” instead of “should.”
- Define terms, symbols, and acronyms (include a “Glossary of Terms”).
- Avoid redundancy—state everything, but only state it once. If information is on the drawings, don’t repeat it in the specification Define each aspect of the requirement in one or two paragraphs where possible.
- Ensure consistency and accuracy—use simple terms throughout the specification (e.g.,“use,” “supply,” “submit”). Avoid the following:
- Nominating specific control functions to particular persons (e.g.,architect, engineer) unless this is intended.
- Listing overly specific or immeasurable requirements such as “best trade practice,” “first-class work,” or “acceptable standard.”
- Apply logic—specifications should:
- Have subheadings and a logical numbering system for all headings. Cross-referencing within the specification should be kept to a minimum because of possible future updates.
- Not specify for failure, such as specifying repairs following damage. This is for the conditions of contract to resolve.
- Be outcome-focused by stating what is to be achieved, instead of how it is to be done.
There are no fixed rules on formats and structures because every specification reflects a different requirement based on project scope. A specification should list the functional, performance, and technical characteristics separately.
It is important for specification writers to rely on technical data sheets to make educated decisions. Technical data sheets (also referred to as product data sheets) provide technical specifications, product attributes/features, substrate and system recommendations, limitations, and other important product information.
While the coating selection process is crucial, what is often neglected is consideration of the substrate being coated. Without ensuring that appropriate substrate-specific preparation takes place, the resulting performance of the coatings could be compromised.
Surface preparation
Many coating issues result from inadequate or improper surface preparation. All substrates must be dry, in sound condition, and free of oil, dust, dirt, mildew, rust, or other contamination prior to coating application. Selection of the proper method for surface preparation depends on the substrate, the environment, the coating selected, and the expected service life of the coating system. The following provides an overview of proper surface preparation for a variety of common building substrates.
Drywall/gypsum wallboard: Joints must be taped and covered with a joint compound. Fill nail heads and sand tape joints to provide a smooth flat surface. Avoid heavy sanding of the adjacent wallboard surfaces, which will raise the nap of the paper covering. Remove dust from the surface by wiping with clean rags or other means prior to painting. On exterior installations, drywall surfaces must be patched with exterior grade patching compounds.
Concrete & masonry: Allow 30 days to cure, and pH must be below 10 prior to coating application. On tilt-up and poured-in-place concrete, removal of curing compounds, bond breakers, and form release agents has to be done prior to any coating application. On concrete floors, special preparation may be required such as acid-etching—up to and including abrasive blasting.
BEHR PRO Concrete & Masonry Primer provides excellent adhesion to smooth, vertical above-grade concrete and masonry surfaces, as well as outstanding alkali and efflorescence resistance.
Wood: Prime and paint exterior wood as soon as possible. Patch all nail holes and imperfections with a suitable patching material and sand smooth. Fill all gaps with a high-quality caulk or sealant. On interior, all finishing lumber and flooring must be stored indoors to prevent moisture absorption, shrinkage, and roughening of the wood.
BEHR Acrylic-Alkyd Enamel Undercoater is specially formulated to have outstanding flow and leveling application similar to oil-based primers, but with easy soap and water clean-up. This product has a quick dry time and blocks medium to heavy tannin stains—making it an ideal primer choice for painting interior or exterior wood.
Steel: The surface preparation required for different types of coating systems to be applied over steel will vary considerably depending on the type of coating as well as the service environment. Basic standards for preparing metal substrates have been established through a joint effort between the Society for Protective Coatings (SSPC) and the National Association of Corrosion Engineers International (NACE).
BEHR Interior/Exterior Metal Primer is a rust-inhibitive primer that can be applied over clean and sound rusty metal surfaces while preventing corrosion with minimal surface preparation. This innovative water-based primer features fast dry time, low odor, and easy clean-up.
Galvanized metal: Allow galvanized metal to weather a minimum of six months prior to coating. Remove any oils or surface treatment with solvent or degreaser.When weathering is not possible or the surface has been treated with chromates or silicates, first solvent clean and apply a test area, priming as required.
Previously coated surfaces: Glossy surfaces of old paint films must be clean and dull by sanding before repainting. All surface contamination, such as oil, grease, loose paint, dirt, rust, mold, mildew, efflorescence, and other foreign, matter must be removed.
BEHR Interior/Exterior Bonding Primer is specifically formulated to bond to a variety of “tough-to-paint” surfaces. Its advanced chemistry provides a sound anchor for topcoats while reducing or potentially eliminating the need for sanding dense and glossy surfaces.
Understanding coating failures and how architects can help prevent them is important in specifying the proper coating system. Oftentimes, architects and designers discover that products do not meet the requirements as specified until after the submittal. The guidelines outlined here are intended to help in mitigating the probability of such occurrences.
For product and specification questions, contact your BEHR Architectural & Design Representative.
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