The coastal line — aluminium, done properly
Preview — not yet in production Preview — read this firstCoastLine is specified but not yet in production. This page is the specification we are building to, published in advance so you can evaluate it. It is not available to order today.
| Post, outer size | 50 × 50 mm (1.97 × 1.97 in) |
|---|---|
| Post wall | 3.0 mm (0.118 in) |
| Material | 6061-T6 aluminium |
| Grade | 6061-T6 — not 6063, see below |
| Finish | AAMA 2605 fluoropolymer powder, matte black RAL 9005, over a coastal-grade pretreatment — see below |
| Post weight | 1.52 kg/m — half the steel lines |
| Guard heights | 36 in and 42 in |
| Guard rail top rail | 50 × 50 mm square |
| Cable top rail | 2 × 1 in × 3.5 mm, 4 ft max span |
| Base plate | 115 × 115 × 10 mm, 4 × Ø11 mm holes at 3.25 in centres, 5/8 in edge distance |
| Height | Safety factor | Load case |
|---|---|---|
| 36 in | 2.26 × | 200 lb concentrated, any direction (IRC R301.5) |
| 42 in | 1.29 × commercial case | 50 lb/ft uniform = 300 lb per post at 6 ft spacing (IBC 1607.9.1) |
We hold no ICC-ES evaluation report and no Intertek CCRR. Every figure here is our own engineering against published code requirements and published material minimums. It is not a third-party rating. The full working, with a live calculator, is on our Engineering & Code Compliance page.
6061-T6 has a 240 MPa minimum yield against Q355 steel’s 355. The extra wall is what buys back the difference, so CoastLine lands at 1.29× against ProGuard’s 1.34× on the same governing case. Same outer size, same fittings, same strength — and half the weight.
6063-T6 is the cheapest and most common Chinese extrusion alloy, and at our section it gives 0.91× — it fails. 6005A-T6 gives 1.15×. Only 6061-T6 reaches 1.29×. The substitution is invisible to the eye, so we require a mill certificate for every heat.
Aluminium’s lower yield applies to the rail as much as the post. At 2.5 mm the aluminium cable rail carries 0.95× — it fails; it needs 3.5 mm to reach 1.21×. We found that by driving the calculator on our own engineering page after the material decision, which is rather the point of publishing one.
A stainless cable through an aluminium post is a galvanic couple at the drilled holes — where the coating is cut and salt concentrates. So the spec is fixed: AAMA 2605 fluoropolymer finish, never 2604; e-coat beneath the powder, which reaches into the recesses where corrosion starts; and isolating bushings at every cable pass-through and stainless fastener. Those are in the specification, not left to the factory.
Anodising is its own finish system, not a pretreatment under powder, and its architectural palette is the champagne-to-bronze-to-black family. Black is achievable; repeatable MATTE black, batch to batch and against a replacement post you buy three years later, is not. That disqualifies it for a product line on its own. On corrosion, a finisher who does both systems puts it plainly: “PVDF is relatively chemically inert and will outlast anodizing in corrosive environments.”
“The vast majority of powder coat failures can be put down to poor or inconsistent pre-treatment methods.” So our specification carries a number the factory can be held to and incoming inspection can check: etch weight loss ≥ 2 g/m², the QUALICOAT “Seaside” class, reported per batch. “AAMA 2605” describes the powder and says nothing about what is under it.
We permit one alternative to the etch: a 4–8 µm pre-anodise, left UNSEALED, powder coated within the anodiser’s hold time. Both words carry weight. QUALICOAT credits it with “totally remov[ing] all the grain boundaries, so there are no places where filiform corrosion may take hold.” A sealed anodic film under powder is the expensive wrong version of the same idea.
Our cable holes cut the coating at the one place salt collects, so every cable, drain and mounting hole is machined, deburred and radiused to a minimum 0.5 mm before pretreatment — not after. A sharp edge or a burr cannot hold film thickness, and a hole drilled after coating is bare aluminium in the worst possible spot. Which is also why you must never drill a post on site.
AAMA 2603 is 1,500 hours of salt spray, 2604 is 3,000, and 2605 is 4,000 plus a ten-year South Florida exposure. Viewrail uses 2604 on its entry system — which it states sits outside its coastal warranty — and 2605 for coastal. Feeney is 2604. Superior Aluminum is 2603. 2605 is above every maker we checked.
Read the exclusions on any railing warranty before buying for a coastal site. It is common for the clause voiding cover for “salt spray, salt air… surface oxidation” to sit in the warranty of a product marketed for marine use. One major brand drops aluminium to a one-year warranty within a mile of the water. We are not going to pretend aluminium is indifferent to salt — we are going to specify the finish and the isolation that make it hold, and ask you to rinse it with fresh water on a schedule.