This inspection took place 18 months after an installation of Metalseal, our BBA Approved metal roof coating system.
The surveyors noted that rust was appearing through the coating, where the cut edges had been treated with our SWT (Surface and Wet Tolerant) corrosion primer.
We were able to demonstrate that no corrosion was present through the coating and that the “rust” in question was in fact rust staining.
Rust staining occurs when there is corrosion present to the underside of the roof sheets. In this case, as part of the Metalseal installation, an old, existing cut edge corrosion treatment that was trapping moisture, was removed as part of the process.
It is not possible to treat underside corrosion without removing fixings and lifting the sheets, which is impractical.
However, by wiping the surface of the Metalseal coating with a damp cloth, you can see that the staining is not compromising the coating system.
In fact, this roof is performing exactly as we would expect and as per the original roof specification.