THURSDAY, SEPTEMBER 5, 2013
Editor's Note: This article was written by MPI (Master Painters Institute), based on material adapted from its Level 2 Maintenance Repainting Coatings Specialist course. Reprinted with permission from MPI News and MPI online training.
Repaint projects run the gamut, from freshening up an intact system to recoating a severely degraded surface—but regardless of the project complexity, there are steps that must be taken to assure success.
First, we believe that if you’re going to write a repainting spec, you (or your representative) must first visit the site to evaluate the existing condition of the surface. And second, there are facts you need to know about the current coating system and service environment in order to specify a system that is compatible.
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| Photos: MPI |
Here’s a checklist of steps to take before writing a repaint spec.
Assessing the Existing Surface
The Importance of a Jobsite Inspection
We can’t imagine writing a spec for a commercial repaint project without first visiting the job site. It’s not enough to get a description of the existing condition over the phone or from someone at the site sending pictures.
The surface must be personally inspected by a professional who’s knowledgeable of good painting practice and the evaluation steps described below—which almost always means not the Superintendent of Maintenance or someone on the Board of the institution whose assets are being painted.
We also realize that when the project requires freshening up a surface that appears to be intact, the owner or specifier may be tempted to skip the inspection and assessment steps described below. However, appearances can be deceiving!
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What looked like a simple color change results in dramatic failure. |
We discussed in a past MPI newsletter a project where a wall coating that looked to be completely sound was actually thoroughly delaminated from the layer underneath it, but since no inspection was done, the flaw only became apparent after a fresh repaint system was applied that pulled up all the delaminated coating underneath.
A simple inspection and adhesion test would have been a lot less costly than cleaning up the resulting failure. And just last month, we described how an intact elastomeric wall coating can fail if the increased film build from one additional repaint eliminates its ability to breathe.
A thorough inspection of the condition of the existing coating should include an evaluation of:
Higher-build coatings can create additional stress by adding weight to the existing film. So specifying a high-build coating for repaint work on a surface with compromised adhesion could require complete removal of the existing coating—which may not fit with the budget.
The ASTM D3359 Tape Test is a common way to determine the adhesion of the existing coating. The test may be conducted by making an “X” cut through the coatings to the substrate, then applying and removing an adhesive tape designed for the test. A rating of 3A indicates that more testing should be done; a rating of 1 or 0 virtually guarantees that full removal will be required.
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Loose chalk on a painted surface should be evaluated. |
Do Some Detective Work
The inspector or specification writer will also need to do some detective work to determine the following:
Be warned that writing a repaint spec before you know what you’re topcoating can be risky business: Some types of coatings cannot be easily topcoated, or are incompatible with other types of coatings.
If you know the existing coating type has compatibility or topcoating issues, additional steps must be taken that may include applying a transition coat or bonding primer, or resigning yourself to extensive preparation or even total removal of the existing coating.
Or, the film may contain lead. If so, the repaint spec (and the budget for the project) may change dramatically to meet health and environmental requirements. And if you hear "well, we haven't had the budget to fix it so that paint's been peeling for five years" (or 10 years), that's an immediate red flag that total removal of the existing coating may be required.
Inadequate surface preparation prior to initial coating application. If this is the case, applying a new coat over a system with poor underlying surface preparation is like building another story on a house with a shaky foundation. Complete removal and re-prepping the surface will very likely be required.
Flaws or defects in the substrate from, for example, water ingress from a construction defect. Whatever caused the failure must be rectified (e.g. find and fix the leak!) before coatings work commences, or any new system is likely to fail again for the same reason.
The coating type specified was inadequate for the service requirements, and a different product should be specified for the repaint work.
When buildings change hands or purpose or undergo renovation, a floor that was previously a storage area may now be repurposed for forklift traffic; an exterior wall that was previously adjacent to another building is now facing a parking lot bathed in sunlight, etc. In these cases, the coating that performed successfully in the past may not be appropriate for the current condition.
Once the existing surface has been inspected and its condition assessed, the specifier will know how much surface preparation will be required, and whether the surface is sound enough for touch-up only, or degraded enough to require spot priming or even full application of a primer, intermediate, and topcoat.
Other Considerations
Once you’ve answered the questions above, items that still need to be considered before choosing a repaint system include the following:
Current Environmental Regulations
We see plenty of projects where the coating products used on a structure in previous years no longer meet the current environmental regulations for that location. So before you specify a re-coat with the same product as the last time, verify that the preferred coating system is still allowed in this particular area.
Surface Preparation: What’s Possible?
Once the specifier has the surface assessment described above, he/she knows what surface preparation will be required prior to repainting. Inadequate surface preparation is the leading cause of premature paint failure, and coating types vary in their ability to tolerate less-than-ideal surface preparation.
So the specifier must take care to choose a repaint system that is adequate for the surface cleanliness that may be realistically attained under job conditions. Repaint projects often have inherent limitations as to what tools or methods may be used for surface prep, including limited accessibility; restrictions on generating dust or debris or noise; or potential for damage to nearby equipment or machinery.
Once these limitations are known, the specifier can choose the best finish system for the exposure within the limits of what surface preparation methods may reasonably be used for the job.
Exposure Environment: What Worked There May Not Work Here
One of the foremost responsibilities of the paint specifier is to consider the ambient exposure environment the coating is likely to face each day of its service life.
Exterior environmental conditions that can affect coatings performance include wind, rain, low temperatures, high temperatures, UV rays, chemicals, and general pollution. Coatings that perform well in humid and salt spray conditions may fail prematurely in areas of high ultraviolet exposure, while coatings suitable for dry areas with high UV may fail in humid environments—and to complicate matters further, most coated structures experience a combination of exposure environments.
Interior environmental conditions that can affect the coating(s) may include high traffic, chemical exposure (labs, chemical plants), wet or humid interiors (pools, gyms, ice rinks), cooking fumes and food debris (restaurants, kitchens), tobacco smoke, dust, high or low temperature variations, and soap residue.
The environments encountered in building interiors can be more varied and complex than those on the exterior. For example, the school hallway has to resist far greater contact than the walls in the principal’s office; its janitorial closets face chemical splash/spill; and food prep and cafeteria walls must withstand regular cleaning with harsh chemicals.
Different products may be required in each area in order to assure the owner achieves the desired service life and duty cycle for the applied coatings.
Restrictions with Occupied Spaces
Coating selection must also consider the additional challenges faced if the building is occupied during repaint operations. These can include odor, application restrictions (spray versus brush and roller), required ambient conditions during paint application, required drying times, and dry fall properties.
Unfortunately, sometimes the coating system that provides optimum performance for the exposure environment may not be compatible with the restrictions imposed by building occupation. In these situations, decisions must be made that weigh short-term inconvenience with long-term protection.
To help specifiers write good repaint specs, MPI standards include five Degrees of Surface Degradation (DSD) with suggested paint systems and surface prep requirements for each. We'll cover these in another installment.
Tagged categories: Chalking; Coating failure; Delamination; Education; Good Technical Practice; Maintenance coating work; Master Painters Institute (MPI); Painting Contractors; Specification; Specification writing; Surface preparation
