When a coating fails, it is almost never the paint

When a coating lets go inside a season, the paint gets blamed and the supplier gets phoned. In our experience the paint is rarely the problem. The surface it went onto is.

Three ways prep fails

1. Residual corrosion

Rust left in a pit or a seam keeps working under the new film. The coating looks fine for months, then blisters in a pattern that maps exactly onto what was left behind.

2. No surface profile

Coatings need mechanical key. A smooth, polished or previously sealed surface gives the film nothing to grip, so adhesion depends entirely on chemical bond — and that is not enough on steel that flexes, heats and cools.

3. Partial removal

Leaving sound-looking old coating in place assumes the old film is still bonded. If it is not, your new system is only as strong as whatever it was applied over.

Surface preparation is not cleaning. Cleaning removes what is on the surface. Preparation changes the surface so the next system holds.

Matching the method to the substrate

A bin lid, a pressure vessel, a truck frame and a concrete slab are four different jobs even when three of them are steel. Media, pressure, standoff and technique all change with substrate condition, the coating being removed, and the standard the next trade needs.

This is also where the wet/dry decision lives. Dry is faster and right for heavy steel and concrete. Wet cools as it cuts, which is what saves thin sheet from warping — and what lets us work next to a running operation without a dust cloud.

Flash rust is a real deadline

Bare steel begins oxidising as soon as it is exposed. We carry rust inhibitor in the blast water, which holds the surface long enough to coat, but it is not indefinite. The blast and the coat need to be planned as one sequence, not two bookings that happen to be near each other.

The same failure turns up on equipment from yards near Seven Persons and on steel coming out of the shops in Brier Park Industrial. The substrate changes; the reason the coating let go does not.