Edges Lose the Paint First

The Wet Edge, No. 007. Short field notes for coating crews.

Walk any old steel job and look at where the rust starts. It's the edges, the welds, the bolt heads and the back-to-back angles. It's almost never the middle of the flange.

That's physics, not bad spraying. As a coating dries, surface tension and shrinkage pull it away from a sharp edge. The film there ends up thinner than the gauge reading on the flat right next to it, like honey sliding off the edge of a knife. Spray also tends to bridge over weld crevices instead of getting down into them.

A stripe coat fixes both. It's an extra coat, usually brushed, on edges, welds, bolts and corners only. The brush pushes material into the crevices a gun skips. On blasted steel it usually goes on after the primer, so the edges don't rust back while you wait.

Why it matters: edges are where a lot of coating systems fail first, and in immersion that's a warranty call. Plenty of specs require a stripe coat, and inspectors look for it. Estimators, carry it in the bid: it's labor and material.

The practical move: when the data sheet allows it, tint the stripe coat a contrasting color so the crew and the inspector can see what's been hit. Keep it inside the recoat window of the coat it goes over.

Bottom line

Edges pull thin no matter how good the sprayer is. Brush a stripe coat on edges, welds and bolts, and make it easy to see.

Further reading: Importance of Stripe Coating for Extending Coating Service Life (KTA-Tator). Standards: SSPC Paint Guide No. 11.

Talk to a consultant. Questions on a job? Atlantic Coating Consultants supports contractors in PA, NJ, DE, MD, DC, WV and OH with product recommendations, field support and crew training. Call 484-644-5303 or email atlantic@tnemec.com.