TRANSPORT INFRASTRUCTURE
Bridges & Transport Structures
Protective systems for bridge steelwork, gantries and access structures, from new construction to planned refurbishment.
ALKA PROTECTIVE COATINGS
Corrosion protection for structures built to connect.
Bridge steelwork is exposed to weather, moisture and, in coastal locations, salt deposition. ALKA provides system options that combine corrosion protection, barrier performance and finish retention, with maintenance alternatives where full abrasive blasting is restricted.
New exposed steel
Bridge girders, trusses, gantries and handrails requiring a coordinated primer, epoxy barrier and external finish.
Coastal atmosphere
Steel above the waterline exposed to salt-laden air. Select the coating build for the actual exposure and maintenance plan.
Existing structures
Refurbishment areas requiring assessment of old coatings, corrosion, soluble salts and achievable preparation.
UNDERSTAND THE SERVICE
Design the coating around the bridge, not just its colour.
Different exposure on one structure
Open girders, sheltered undersides and coastal members may experience different wetting and salt deposition. Map atmospheric, splash and immersed zones before assigning a coating schedule.
Edges, welds and connections
Protection depends on the detail as well as the broad surface. Include edge and weld preparation, stripe coating where specified, and inspection access around bolts, joints and other difficult geometry.
Maintenance access and old coatings
Scaffolding, containment and traffic restrictions affect the available preparation method. Assess the condition of retained coatings and define repair boundaries before deciding between local repairs and full refurbishment.
ALKYD PRIMERS · ENAMELS · SINGLE-PACK FINISHING
Keep ancillary enamel work distinct from bridge protection
Single-pack finishes may be considered for selected sheltered service cabinets, workshop items and other ancillary metalwork with ordinary atmospheric duty. Primary bridge steel and assets with defined durability or road-authority requirements need the relevant engineered coating system.
Products to assess for the job
- ALKA 401 · Alkyd zinc phosphate primer
Prepared carbon steel; a corrosion-inhibiting primer for compatible alkyd and enamel finishing routes.
- ALKA 403 · Red oxide anti-corrosive primer
A primer option for prepared ferrous metal, fabricated steel and general maintenance; confirm the selected finish compatibility.
- ALKA 410 · Rapid-cure protective enamel
A gloss finishing option for machinery, fabricated components and maintenance work over a compatible prepared and primed surface.
Select a complete, compatible primer and finish. The products above are options by role, not a blanket approval to combine every primer and topcoat.
What the applicator or specifier needs
Identify which items belong to the bridge protection specification and which are separate ancillary finishes. Confirm asset owner requirements and exposure by location.
Assess retained coating, corrosion, salt contamination and preparation access. Detail edges, welds and connections before choosing a maintenance coating.
Define colour and gloss, inspection access and repair of installation damage. Keep ancillary product schedules distinct from the primary structural specification.
Write a usable coating schedule
Specify the substrate and preparation, exact primer and finish, individual-coat dry-film thickness, application method, thinning limits, recoat interval and service-cure requirement from current product data. For repainting, document the retained coating and a representative compatibility trial before full application.
Choose the coating for the exposure
Do not substitute a general enamel for the specified bridge system, severe coastal protection, tidal exposure or immersed-pile lining.
A single-pack route can simplify small batches and routine repainting because it does not require mixing a separate hardener. It still depends on sound preparation, suitable film build and the correct recoat window. Where exposure or the required maintenance interval is more demanding, assess the relevant two-pack epoxy, polyurethane or specialist lining system.
Does fast drying mean the part is ready for service?
No. Touch-dry, recoatable, handleable and fully cured describe different stages. Use the selected product data and actual application conditions to plan each stage. Excessive film build, early overcoating or premature handling can compromise the finish; adding extra thinner or a hardener is not a substitute for the specified application procedure.
SYSTEM SELECTION
ALKA systems to consider.
Start with the service conditions, then confirm the complete build for your asset.
| System | Coating build | Nominal DFT | Selection note |
|---|---|---|---|
| ALKA-9930 Premium External | Alka 404 zinc-rich epoxy primer → Alka 413 high-build epoxy → Alka 421 polyurethane finish | 250–300 µm | Preferred where long-term durability and appearance are both important. Not an immersion system unless separately approved. |
| ALKA-9933 High-Barrier Atmospheric | Alka 404 or Alka 416 primer → Alka 413 MIO high-build epoxy barrier coat | 225–275 µm | May remain as an MIO finish where colour and gloss are secondary. Add a compatible finish coat when aesthetics or UV retention are required. |
| ALKA-9932 Maintenance / Refurbishment | Alka 412 surface-tolerant epoxy × 2 coats → optional Alka 421 polyurethane finish | 200–400 µm plus optional 50–75 µm finish | Existing coatings require compatibility and adhesion assessment. UV finish is optional where colour retention is required. |
| ALKA-9938 Marine Atmospheric | Alka 404 zinc-rich epoxy primer → Alka 413 high-build epoxy → Alka 421 polyurethane finish | 275–325 µm | For atmospheric marine exposure only. Tidal, splash and permanent immersion zones require a dedicated high-build lining system. |
DFT = dry-film thickness. Values are nominal selection-guide totals, not wet-film thicknesses or individual-coat application instructions. Use current TDS and written project-specific recommendations.
FROM EXPOSURE TO SYSTEM
Why these systems are considered.
Use the application and preparation requirements to narrow the options, then confirm the complete specification.
New exposed carbon steel
The zinc-rich primer, high-build epoxy and polyurethane finish combine primer protection, a barrier layer and an external finish. This is a starting point for fully specified new-steel work, subject to exposure and preparation review.
Barrier-focused atmospheric areas
The MIO epoxy barrier build offers a different route where barrier performance is the focus. Establish the appearance and weathering requirements explicitly rather than assuming the same finish as a polyurethane-topped system.
Maintenance and refurbishment
Consider the two-coat surface-tolerant epoxy build when working with existing steel and approved retained coatings. The optional polyurethane finish addresses external appearance where required; it does not replace preparation.
Coastal atmospheric steel
This build is intended for marine atmosphere above the waterline. Use the actual exposure boundary to distinguish it from coatings for splash, tidal or permanently immersed components.
SPECIFICATION CHECKPOINTS
Get the details right before coating.
- 01Atmospheric, splash or immersed exposure by zone
- 02Edge, weld and bolted-connection detailing
- 03Soluble-salt removal and surface-profile requirements
- 04Access restrictions and compatibility of retained coatings
THE SYSTEM APPROACH
ALKA-9930 example. Nominal total dry-film thickness: 250–300 µm. Diagram is not to scale. Confirm individual coat thicknesses in the approved specification.
Confirm surface preparation, stripe coating, application conditions, recoat intervals and cure. Record inspection results against the approved coating schedule.
APPLICATION & QUALITY PLANNING
Build inspection into the specification.
Agree the acceptance criteria before work starts, with the current product data and project coating schedule as the reference.
01 · Accept the substrate
Record substrate condition, cleanliness and the specified surface preparation. Resolve contamination, unsound existing coatings and detailing before the first coat.
02 · Control application
Confirm environmental limits, mixing, usable application time and recoat windows from the current product data. Record coating batches and the conditions during each stage.
03 · Verify the complete build
Check coverage at edges and details, specified individual-coat thickness and total dry-film thickness. Define how defects will be repaired and re-inspected.
04 · Release to service
Record repaired areas, coating batches, individual and total DFT, final finish and access arrangements for future condition inspections.
TECHNICAL QUESTIONS
Details that change the specification.
Can sound existing paint be retained?
Potentially, after its condition, adhesion and compatibility are assessed. Define cleaning, removal of unsound material, preparation of exposed steel and treatment of transition edges. Agree a trial area where compatibility or appearance is uncertain.
Does a thicker coating automatically give a longer service life?
No. Total thickness is only one part of the specification. Preparation, individual-coat limits, coverage at details, cure, environment and maintenance all matter. Apply the approved schedule rather than increasing thickness without technical review.
Can an atmospheric bridge system also protect submerged piles?
Do not extend it on that basis. Piles can cross atmospheric, splash, tidal and immersion zones. Each zone needs a suitable approved build, including its preparation, cure and inspection requirements.
TECHNICAL RESOURCES
Move from selection to specification.
Coating system library
Compare ALKA system builds for atmospheric, maintenance and lining applications.
Browse systems →Product information
Explore product information and request current technical and safety data sheets.
Technical information →Specification support
Confirm preparation, products, film thickness and service conditions with ALKA.
Contact technical team →SPEAK WITH THE MANUFACTURER
Specify the right protection.
Send the substrate, exposure, existing coating condition and required finish. Our technical team can help identify a suitable ALKA system and the information needed for your specification.