Coatings can rejuvenate a metal roof, adding years to its useful life and delaying the need for a far more costly and disruptive replacement. But coating systems are not “miracles in a bucket” or “one-size-fits-all.” Complete these steps before coating a metal roof
Article originally appeared in the September 2026 issue of Metal Construction News: https://www.metalconstructionnews.com/publications/de/202609/
Assess. Repair. Test. Coat.
Essential steps before coating a metal roof
A properly applied roof coating system can rejuvenate an aging metal roof, brightening its appearance, enhancing its energy efficiency, and delaying the need for a far costlier and more disruptive roof replacement for years.
But coatings are not “miracles in a bucket”. They will not make an unsound roof sound; unsound roofs must be replaced. Nor will they magically fix pervasive leaks, ponding water, and other performance problems; these issues must be addressed prior to coating, or the newly restored roof is likely to fail prematurely. And coating systems are not “one-size-fits-all”. The chosen solution must be compatible with the existing roofing system.
The first steps, then, in any successful coating job are to complete a thorough visual inspection of the roof, make any needed repairs, and complete an adhesion test.
Visual inspection of the existing roof
No two roofs are the same. It is, therefore, essential to walk the roof and experience it up close. Trash and debris should be removed to provide an unobstructed view of the existing roof. Among the things to then look for are:
• Peeling and chalking of existing coatings.
• Areas of heavy rust. (The roof can likely still be coated but will require an extra-thorough cleaning followed by priming to ensure proper adhesion of the new coating.)
• Poorly attached vents or other projections.
• Open seams and side laps.
• Insufficient slope.
• Areas of ponding water (evidenced by the accumulation of dirt or debris).
• Broken or improperly flashed pipes.
• Broken or missing drain components.
• Loose or damaged perimeter edge metal.
• Deteriorated, damaged, loose, or poorly installed flashings.
Repair existing issues
As mentioned above, roof coatings are not magic cure-alls. Neglecting to correct underlying issues before coating will inevitably result in the coating failing prematurely. Instructions from the coating manufacturer should be followed. In general, the existing roof assembly must be structurally sound and watertight, and free of shrinkage, unacceptable ponding conditions, encapsulated moisture, open seams, open or damaged flashings, loose terminations, and other serious defects. Penetrations, terminations, skylights and other leak-prone areas must be properly sealed. Particular attention should be paid to the transitions between the roof and parapet walls; the two areas respond differently to building movement and temperature swings, making the areas where they meet prime spots for leaks to appear. Pitch pans should be installed around HVAC units to ensure that their vibration does not create pathways for water to enter the roofing system.
The good news is that, even when a roof shows significant damage, some simple repairs can make it a viable candidate for coating. The following examples illustrate some common scenarios.
Problem: The roof panels have rusted. Solution: If the panels remain structurally sound, prepare them as follows prior to coating: remove loose rust using a wire brush, wire wheel, or electric sander; clean the panels thoroughly and allow them to dry; apply primer to encapsulate the remaining rust. If some panels are corroded to the point that they are no longer structurally sound, replace them. The remaining panels can be left in place.
Problem: The roof has an area that is susceptible to ponding water. Solution: Fill the ponding area with slope-correcting material or correct the slope with an approved surface-leveling product that can fill in low-lying areas to provide positive slope. Additional or upgraded drains may also be needed to create positive drainage.
Problem: There are active leaks. Solution: All active leaks must be identified and repaired before the new coatings system is installed.
Complete an adhesion test
A coating’s long-term performance depends on how well it adheres to the substrate. An adhesion test should be performed to ensure that the chosen coating will stick. First, the test will check compatibility between the coating and the substrate. It can be difficult to determine by eyesight alone the type of factory-applied finish on the panels or the type of coating used in a previous restoration, but that information is crucial to choosing the right coating system. For example, Kynar 500® must be treated with special primers before being coated with silicone or acrylic, and a roof that was previously restored with acrylic can be recoated with acrylic or a silicone, but a roof that was coated with silicone can only be recoated with silicone. An adhesion test will eliminate the guesswork.
Second, the adhesion test can uncover issues with the existing roof that were not apparent during the visual inspection—in particular, the presence of moisture that has infiltrated and become trapped in the roofing system.
Instructions from the coating manufacturer should always be followed when performing the adhesion test, but here are a few general guidelines:
• Select a 2 x 2-ft area of the roof as the test site. Clean the area using a rag or bristle brush and a solvent that will flash off quickly without leaving a soapy residue behind, such as acetone, xylene, or mineral spirits.
• Coat a 1 x 1-ft section of the test area, replicating what the finished system will be. If the roof is to be primed, then prime the test area. Apply primer and finish coats at the same application rate that will be used to coat the entire roof.
• Embed several strips of Tietex or other polyester-reinforced fabric, each measuring roughly 1 x 12-in., into the coating, leaving a 4-in. long pull tab outside of the wet area. Brush the fabric to embed it into the coating. Apply a second coat of finish coat to ensure the fabric is fully saturated.
• Allow the coating to cure fully, at least four to five days.
• Test the adhesion using a fish scale. For each test strip, tie a knot in the loose, uncoated end of the fabric strip. Hook the fish scale into the knot then, using the scale, pull the fabric straight up. The ideal “pull strength” is at least 4 lb per linear inch (pli) of fabric, or at least 4 pli over a sound and dry substrate.
• The adhesion test is a “Pass” when the fabric separates from the coating, leaving the coating still adhered to the roof membrane. The test is a “Fail” if the coating separates completely from the roof surface.
All adhesion tests should be documented with photos of the cleaned substrate, the wet coating and embedded fabric, and the face or display of the fish scale showing the resistance observed in the test.
Success starts before the coating
A roof coating system can bring new life to an aging low-slope metal roof, provided the existing roof is sound, performance issues are addressed, and the selected coating is compatible with the existing roofing system. Every coating project should start with a thorough inspection of the existing roof, making any needed repairs, and completing an adhesion test.
These three simple steps will help ensure the restored roof delivers years of watertight, hassle-free, lowmaintenance protection
About the Author
Lane Reed is a regional director with low-slope roofing manufacturer MuleHide, leading the Southwest region. A 23-year veteran of the roofing industry, he joined MuleHide in 2016, serving as a territory manager in Central, Southern and West Texas for seven years. He began his roofing career as a sales representative and estimator with a commercial roofing contractor and later sold commercial and residential roofing materials as a manufacturer’s representative.