Steel tower and lattice structure painting: aged zinc, access and safety

A lattice tower is painted when its galvanizing is running out or its paint is breaking down, before rust attacks the angles and bolted connections. The job rests on three choices: preparing the aged zinc (washing, removing zinc salts and rust, a light profile), a primer compatible with zinc, and safe access at height, by rope or aerial lift, under a fall protection plan.

Telecommunication towers, masts, equipment supports and other lattice structures are almost always hot-dip galvanized. Zinc protects the steel for a long time, but it is consumed, faster in industrial or coastal atmospheres and where de-icing salts reach the steel. Once it is exhausted in places, maintenance painting extends the structure's life at a fraction of the cost of replacement. This guide is for owners and managers of towers and lattice structures in Quebec and Ontario.

When should a galvanized tower be painted?

A galvanized tower should be painted when the zinc layer becomes thin or discontinuous, but before red rust spreads and pits the steel. Painting too early adds nothing; painting too late forces heavy preparation and member replacement.

Signs to watch for during an inspection:

• Uniform dulling. The zinc has oxidized normally. Protection is still in place.
• Spot red rust. Zinc is exhausted in places, often on edges, horizontal faces and areas where water sits.
• Rust at connections. Bolts, nuts, gusset plates and contact areas rust first, as our article on bolt and connection corrosion protection explains.
• General rust or scaling. The steel is losing section: a structural check comes before painting.

The extent of rusting is rated reproducibly with a method such as the one in our article on ASTM D610 rust grade assessment. Repeated at each inspection, this rating helps pick the right time to act.

How is aged zinc prepared before painting?

Aged zinc is prepared by removing what stops paint from adhering: oils, soluble salts, white zinc corrosion products, rust and flaking paint, then roughening the surface lightly without removing sound zinc. The reference practice is described in ASTM D6386.

On a tower, preparation is usually done by hand or power tool, because abrasive blasting at height raises containment and equipment weight issues. The table summarizes common cases.

Power tool preparation grades are explained in our article on SSPC-SP 3, SP 11 and SP 15 power tool cleaning. Zinc touch-up before painting follows our guide to field galvanizing repair to ASTM A780 and our cold galvanizing service.

Which coating system suits a lattice structure?

The system is chosen to adhere to zinc and to touched-up steel, tolerate hand preparation and resist UV and weather. In practice, a primer designed for zinc is applied, often a surface-tolerant epoxy mastic, followed by a UV-resistant polyurethane or acrylic topcoat.

• Primer. It must adhere to zinc without saponifying. Alkyd applied directly to zinc should be avoided. Our article on the duplex system on galvanized steel details compatible primers.
• Intermediate coat. Depending on the corrosivity category, an extra coat builds system thickness and edge protection.
• Topcoat. Polyurethane or acrylic for colour retention and UV resistance.
• Stripe coating. A brushed coat on angle edges, bolts and gussets before the full coat, because paint thins out there.

The corrosivity category and target durability are set to ISO 12944. When the tower carries painted aviation obstruction marking, colours and bands are redone to the applicable marking standard, Standard 621 of the Canadian Aviation Regulations.

How is a tower accessed for painting?

A tower is accessed by three main means: rope access, aerial lift and climbing with fall protection. The choice depends on height, lattice geometry, ground access and the amount of work per level.

• Rope access. Suited to great heights and to structures with poor ground access. Technicians work on two anchor points, with a rescue plan prepared.
• Aerial lift. Efficient on lower sections and on structures reachable by road, with stable, clear ground.
• Climbing and positioning. For small jobs, with harness, lifeline and anchors to the CSA Z259 series of standards.

The lattice means application is mostly by brush and roller: spraying produces drift that is hard to control at height, in wind, above vehicles or buildings. When spraying is chosen, screens and wind limits are set in advance.

What safety rules govern work at height?

Work at height on a tower is governed by a fall protection plan, a rescue plan, weather limits and, on telecommunication towers, management of radiofrequency exposure. These are prepared before the first day on site.

• Fall protection. Anchors, harnesses, energy absorbers and lifelines to the CSA Z259 series and provincial occupational health and safety regulations.
• Rescue plan. A trained crew and rescue equipment stay at the base of the tower during the work.
• Radiofrequency. Near antennas in service, exposure is governed by Health Canada Safety Code 6; power reduction or transmitter shutdown is coordinated with the equipment owner.
• Weather. Wind, freezing rain, thunderstorms and temperature set stop-work limits, for safety and for application.
• Ground zone. A safety perimeter against falling objects and paint drips.

Should you worry about old lead paint?

Yes. On towers painted long ago, check for lead or other heavy metals before any scraping or sanding. Lead changes containment, worker protection and waste handling.

If the old paint adheres well, overcoating with a compatible system can avoid full removal. Our article on lead paint overcoating vs removal compares the two approaches. In all cases, preparation debris is collected on the ground rather than left at the base of the structure.

How should a tower painting program be planned?

A program is planned from an inspection of each structure: rust rating by zone, condition of connections, presence of lead, access and operating constraints. Towers are then ranked so that those where zinc is exhausted are treated first, before the steel loses section.

Each job is documented: photos by face and level, preparation grade reached, products and batches, ambient conditions and dry film thickness readings to SSPC-PA 2. Adhesion of the new system over zinc can be checked by cross-cut testing to ASTM D3359 on a representative area. This record becomes the baseline for the next inspection and shows whether the selected system is holding up on that site.

Maintenance painting of a tower follows the same logic as other steel structures, described in our article on maintenance painting of steel structures. Our steel structure painting service handles inspection, preparation and application, as part of our protective coatings work.

Frequently asked questions

Can paint go directly onto new or aged galvanized steel?

Not directly: zinc must be washed, cleared of white products and lightly roughened, then receive a compatible primer. Without this preparation, the paint peels.

Is it better to regalvanize or paint an existing tower?

On a standing tower, painting is almost always the only realistic option, because hot-dip galvanizing requires dismantling and dipping in a plant. Zinc is touched up at rusted areas, then painted.

Can a telecommunication tower be painted without shutting down antennas?

Sometimes, depending on where the work is and the calculated exposure. Power reduction or shutdown is decided with the equipment owner, applying Safety Code 6.

Which season suits tower painting?

The season when steel temperature, humidity and wind stay within data sheet limits. In Quebec, this often concentrates the work between late spring and early fall.

Our crews and qualified subcontractors work on towers and lattice structures from LaSalle, including in the Quebec region and Ontario. Send the height and type of structure, photos of rusted areas and access constraints through the quote request: pricing on consultation, reply within 24 business hours.