Polyurethane roof coating is a popular choice for protecting flat and low-slope roofs due to its durability and waterproofing abilities. However, one issue that can occur with polyurethane roofs is oil canning, a visible waviness or rippling effect on the surface. Oil canning happens because of stresses from the roof structure settling, temperature fluctuations causing expansion and contraction, or improper application of the coating over an uneven substrate. It’s not typically a direct indication of a leak or structural failure, but it can raise concerns about the roof’s integrity and appearance. Simple diagnostics include a thorough visual inspection on a bright, sunny day to spot uneven reflective patterns or shadows that reveal waviness. A safely done walk on the roof (using appropriate footwear and safety gear) or a drone inspection can help spot these deformations. Checking for loose or poorly adhered sections of coating is also useful. Since this issue often results from underlying substrate problems or application errors, fixing it may require professional assessment.
If you notice oil canning, safely perform a basic examination to ensure there aren't any brittle or peeling sections that could expose the roof beneath, but avoid aggressive poking or scraping that could damage the coating. If the rippling is minor and the coating remains fully adhered, monitoring may be all that’s needed. However, if the waviness worsens or if you detect blisters, cracks, or soft spots, it’s time to call a qualified roofing contractor knowledgeable in polyurethane systems. When speaking with your roofer, ask specifically if the substrate preparation was adequate before coating and how the application technique prevents oil canning. Also, inquire about warranty coverage for this problem as some manufacturers cover oil canning only if certain installation standards were met. Being clear on these points helps ensure you choose a roofer who understands the nuances of polyurethane coatings, protecting your investment and avoiding future costly repairs.