When To Commission A Bridge Coating Survey
The best time to survey a coating system is before it fails widely. Once breakdown turns into general corrosion, maintenance moves from spot repair and overcoating to full removal and repainting, which is far more expensive and disruptive.
- Ahead of a maintenance painting scheme, to define scope, quantities and the right repair approach
- When a general or principal inspection reports coating breakdown or rust staining
- Before the end of a coating guarantee or defects liability period
- When steelwork is being transferred, handed back or acquired
- To build a whole-life maintenance plan and budget for a portfolio of structures
What We Assess
A coating condition survey combines visual assessment across the whole structure with targeted testing at representative and critical locations.
| Check | What it tells you | Reference |
|---|---|---|
| Degree of rusting | How much of the surface has rust breakthrough | ISO 4628-3 |
| Degree of blistering | Size and density of blisters, an early sign of adhesion or contamination problems | ISO 4628-2 |
| Cracking and flaking | Whether the coating is becoming brittle or detaching | ISO 4628 series |
| Dry film thickness | Remaining coating thickness compared with the original specification | Specification requirement |
| Adhesion | Whether the existing system can be overcoated safely | Pull-off or cross-cut testing |
| Paint sampling | Presence of lead or chromates in older systems | Laboratory analysis |
Where Bridge Coatings Fail First
Coating breakdown on bridges is rarely uniform. It concentrates where water, salt and debris collect, or where the coating was hardest to apply well in the first place.
- Beneath leaking expansion joints and around bearings
- Around drainage outlets, downpipes and deck drains
- Edges, corners, bolts and welds, where film thickness is naturally lower
- Splash zones next to carriageways where de-icing salt spray reaches the steel
- Bottom flanges and horizontal surfaces that hold standing water or debris
- Areas damaged by vehicle impact, previous repairs or poor access during painting
Turning Findings Into A Maintenance Plan
The survey report maps defects by location and severity, with photographs, and groups the structure into zones that need no action, local repair, overcoating or full repainting. That gives you a clear scope for tendering and a defensible basis for your maintenance budget.
For work on National Highways structures, repainting is now specified under CC 486 Protection of steelwork against corrosion, which replaced Series 1900 of the Specification for Highway Works in September 2025. We can advise on system selection and the works-specific requirements before the scheme goes to tender, and provide the independent paint inspection during the works.
Access
Most coating surveys need close access to the steelwork. We use IRATA rope access where it reduces disruption, or work from under-bridge units, MEWPs or scaffold where they are already planned. Surveys can also be combined with a principal inspection.