Frequently Asked Questions

What is the typical lead time for custom corten steel planter orders?

Lead time depends on order complexity and quantity. For standard-size planters (rectangular, no custom cutouts or logos) in quantities of 20-100 units, expect 3-5 weeks for production after design approval. Custom shapes with laser-cut patterns or non-standard dimensions add 1-2 weeks for tooling setup and drawing confirmation.

Material sourcing is the biggest variable. Manufacturers who stock corten sheet in common thicknesses (2mm, 3mm, 5mm) can start production immediately. Those who purchase material per order need an additional 1-2 weeks for steel delivery from the mill.

Shipping adds to the timeline: sea freight from manufacturing facilities in Asia to European or North American ports takes 3-5 weeks. Air freight is available for urgent orders but typically costs 5-8x more than sea shipping, making it practical only for small sample quantities or replacement units.

To minimize lead time, provide finalized drawings with all dimensions, drainage specifications, and finish requirements at the quotation stage. Changes after production starts can add 1-2 weeks and may incur revision fees. For time-critical projects, ask your supplier about expedited production — many factories offer rush processing at a 15-20% premium.

How does corten steel perform in coastal or high-humidity environments?

Corten steel’s protective patina forms through wet-dry cycling — the surface needs to get wet and then dry completely for the oxide layer to stabilize. In coastal environments within approximately 1km of saltwater, airborne chlorides interfere with this process. Salt deposits keep the surface damp and prevent the formation of a tight, adherent patina, leading to continued active corrosion rather than protective weathering.

For projects 1-5km from the coast, corten can still work but requires careful detailing. Ensure good air circulation around all surfaces, avoid trapping moisture at joints or bases, and specify 5mm minimum thickness to provide extra corrosion allowance. The patina will form but may take longer and appear less uniform than in ideal inland conditions.

High humidity alone (without salt) is less problematic, provided the steel experiences regular drying periods. Tropical climates with distinct wet and dry seasons allow normal patina development. Constantly shaded, damp locations — such as north-facing walls in temperate climates that never fully dry — can cause issues similar to coastal exposure.

If your project is in a borderline location, request a test panel from your supplier. Install a small piece of corten on site for 3-6 months and observe the weathering pattern. Uniform orange-brown development indicates suitable conditions. Flaking, black spots, or continued heavy rust runoff after 6 months suggests the environment is too aggressive for unprotected corten steel.

What thickness of corten steel is required for water feature applications?

Water features in corten steel require significantly greater thickness than landscape edging or planters due to two factors: the structural loads imposed by water weight and hydrostatic pressure, and the accelerated corrosion that occurs on any surface in permanent water contact.

For the external atmospheric surfaces of a water feature (those exposed to air and wet-dry cycling), standard corten thickness applies based on the corrosivity environment — typically 4-6mm for most applications. However, internal surfaces that remain in permanent water contact do not form stable protective patina. These surfaces corrode at rates similar to mild steel in water (approximately 100-150 micrometres per year in freshwater), which means they require either protective coating or significantly increased thickness as sacrificial allowance.

The industry-standard approach is a dual specification: external surfaces left uncoated to develop natural patina, and internal water-contact surfaces coated with a high-performance epoxy system. For commercial public water features, the typical specification is 6-8mm base steel thickness with a three-coat epoxy system (total 300-350 micrometres dry film thickness) applied to all internal surfaces after fabrication. This provides 15-20 years of protection before coating renewal is required.

For water blade features (where water flows over a corten lip in a thin curtain), the blade lip itself should be minimum 8mm thickness to allow for machining to the required 2mm sharp edge while retaining adequate structural section. The blade backing plate and support structure typically uses 10-12mm plate. Reflection pools and still water features can use lighter sections (6-8mm) as they experience lower dynamic loads, but the base must still support the full weight of water plus maintenance access loads (assume 1.5 kN/m² for a person standing in the drained feature).

Water features in aggressive environments — coastal locations with salt spray exposure, or tropical climates with extended high humidity periods — should increase base thickness by 1-2mm above these recommendations. For projects in Singapore, Malaysia, coastal Australia, or similar environments, specify minimum 8mm for all structural water feature components with internal coating as standard practice regardless of water chemistry.

Can corten steel be welded on site, or must all fabrication be factory-completed?

Corten steel can be welded on site using appropriate procedures, but the decision between factory fabrication and site welding depends on the specific requirements of the project, the skill level of site welders, and aesthetic expectations regarding weld appearance and patina development.

Weathering steel uses specialized welding consumables (electrodes or wire) that match the alloy composition of the base material, including the copper, chromium, and nickel content that enables protective patina formation. Standard mild steel welding rods will create welds that corrode at different rates from the parent corten material and develop visibly different colour and texture in the patina. For this reason, any welding of corten steel — whether factory or site — must use AWS A5.5 Class E8018-W or equivalent weathering steel electrodes for SMAW (stick welding), or AWS A5.28 ER80S-G with appropriate copper-bearing composition for GMAW (MIG welding).

Factory welding is strongly preferred for all primary structural connections, water-tight seams, and any welds that will be visible in the finished work. Factory-controlled conditions allow for proper preheat (corten requires 50-150°C preheat depending on thickness and ambient temperature to prevent cracking), post-weld grinding to achieve flush surfaces, and chemical treatment of weld zones to accelerate uniform patina development. The most critical advantage is quality control — factory welds are produced under supervision with documented weld procedures, qualified welders, and inspection protocols that are difficult to replicate on site.

Site welding of corten is acceptable for secondary structural connections, field assembly of modular components, and repair work, provided that proper procedures are followed. The site welding specification should include: verification that welders hold current qualifications for structural steel welding to relevant standards (such as AWS D1.1 or equivalent national codes); confirmation that correct weathering steel consumables are being used (request mill certificates for welding wire or electrode batches); adequate weather protection during welding (no welding in rain, wind above 15 mph, or temperatures below 0°C without heated enclosure); proper preheat equipment (induction or propane torch capable of achieving specified preheat temperature across the full thickness of the joint); and post-weld treatment (grinding welds flush and applying phosphoric acid wash to promote uniform patina formation).

The critical limitation of site welding is the visible weld zone. Even with proper procedures and consumables, site-welded joints in corten will be visibly different from the parent material for the first 18-36 months of weathering. The weld metal and heat-affected zone initially appear brighter (more orange-red) than the stable brown patina on parent material, gradually converging to a similar colour after several years of exposure. For projects where immediate uniform appearance is required, this is unacceptable — all welds should be factory-executed, ground flush, and chemically treated before shipping to site. For projects where the industrial aesthetic of visible welds is acceptable or even desired, site welding can be embraced as a design feature rather than hidden.

Large landscape elements — water features, retaining walls, planter assemblies — are typically fabricated in transportable modules at the factory and then assembled on site using mechanical connections (bolts with corten or stainless steel fasteners) rather than site welding. This approach provides the quality assurance of factory production while allowing oversized elements to be transported and installed practically. Where site welding is unavoidable for joining modules, those weld locations should be positioned in less-visible areas (internal corners, back faces, base connections) where the temporary colour mismatch during early weathering will not impact the project aesthetic.