Oct 30, 2026Industry News
Hot-Dip vs Cold Galvanized: How We Build a Ladder Lift
Only the main tube of our ladder lift is hot-dip galvanized; the rest is cold galvanized after welding. Here is the engineering reason, and the coating data behind it.
"Galvanized" is not a specification — and "cold galvanized" means two different things
Most RFQs we receive say "galvanized" and stop there. The word names a family of coatings. In hot dip galvanized vs cold galvanized, the real questions are which process, and how much zinc landed on the steel.
Three processes, not two: hot-dip, electro-galvanized, and zinc-rich paint
Hot-dip galvanizing (HDG) immerses steel in molten zinc at about 450 °C; the zinc reacts with the iron into zinc-iron alloy layers — a metallurgical bond, not a coating resting on the surface.
Electro-galvanizing (EG) deposits zinc electrolytically near ambient temperature, with no alloy layer. Typical thickness is about 10–12 µm in manufacturer data. ASTM B633 sets service classes SC1 at 5 µm, SC2 at 8 µm, SC3 at 12 µm and SC4 at 25 µm; ISO 2081 is the matching standard.
Zinc-rich paint is zinc dust in a binder, and the American Galvanizers Association notes that calling it "cold galvanizing" is erroneous. Zinc content behaves counter-intuitively: 65–69% and above 92% perform comparably, while 69–92% is worse. The International Zinc Association cites 77–95% zinc, ISO 12944 sets "zinc-rich" above 80% in the dry film, and SSPC Paint 20 splits the family into inorganic and organic types. Dry film is typically 64–90 µm (2.5–3.5 mils); for touch-up, apply 50% more than the surrounding coating but stay under 4.0 mils.
Ask which one a supplier means. An electroplated part and a painted part behave nothing alike outdoors.
Why buyers ask about salt spray hours (and why that question misses the point for hot-dip)
Datasheets carry a salt spray table because buyers expect one number to rank suppliers. For hot-dip, that number does not exist in any meaningful form. Per the American Galvanizers Association, ASTM B117 tests the wrong object: it measures zinc metal corrosion rather than zinc's protective passivation layer, and runs continuously wet, without the wet-dry cycles that build that layer. A hot-dip coating can "fail" a chamber and still last decades on a roof.
Hot-dip galvanizing vs cold galvanizing: the real differences
Four properties decide the outcome: zinc quantity, zinc attachment, edge behaviour, and the service life it buys.
Coating thickness: 45–85 µm versus 10–12 µm
Batch hot-dip typically lands at 45–85 µm, and the International Zinc Association quotes at least 60–70 µm for general galvanizing. Standards set floors, not targets: ISO 1461 (identical to EN ISO 1461) requires 85 µm minimum average over 6 mm, 70 µm for 3–6 mm, 55 µm for 1.5–3 mm and 45 µm below 1.5 mm; ASTM A123 gives 45 µm up to 1.6 mm, 65 µm for 1.6–3.2 mm, 75 µm for 3.2–4.8 mm and 100 µm for 6.4–16 mm. That is the hot dip galvanizing vs electro galvanizing gap: EG sits an order of magnitude lower. Zinc coating thickness is the number to ask for in writing.
How the zinc bonds: metallurgical versus electrodeposited versus physical
Hot-dip adhesion is metallurgical, with bond strength reported in the several thousand psi range; there is no interface to peel. Electro-galvanizing is electrodeposited, not alloyed — uniform, but a surface layer rather than an alloyed zone. Zinc-rich paint adheres physically and mechanically; inorganic silicate binders add some chemical bonding, but pull-off strength is in the few hundred psi range, an order of magnitude below hot-dip.
Edge protection — where the two processes diverge most
Molten zinc gathers at edges and corners, making them the thickest, most corrosion-resistant points on a hot-dipped part, and hollow sections are coated inside and out. Zinc-rich paint does the opposite: film thickness is thinnest exactly at edges and corners. Electro-galvanized coating is uniform but gains nothing at the edge. Cut ends, drilled holes and folded bracket corners are where water sits and rust starts.
What each one costs you over a service life
Zinc corrodes at roughly one-thirtieth the rate of bare steel. In an ISO C3 environment zinc loss runs about 0.7–2.1 µm per year; American Galvanizers Association averages are 0.75 µm rural, 1.00 suburban, 1.15 temperate marine, 1.26 tropical marine and 1.32 industrial. At 1.3 µm per year, 85 µm of hot-dip zinc buys roughly 65 years and 12 µm of electro-galvanized zinc roughly 9 — not a warranty, but that ratio is what galvanized steel corrosion resistance really means. Within a mile of the coast, exposed surfaces can rust in 5–7 years; sheltered surfaces reach 15–25 years. Zinc-rich paint can be recoated on site, but has lower adhesion, thin edges, and heat limits: about 93–149 °C organic, 375 °C inorganic.
What our ladder lift actually uses — and why it is a mix
The main square tube is hot-dip galvanized. Every other part is cold galvanized. We do not hot-dip the whole machine, and we do not describe it as fully hot-dip galvanized.
The main rail: purchased hot-dip galvanized 40×60 mm tube
The main rail is 40×60 mm square tube, bought from a steel tube supplier already formed and already hot-dip galvanized. In our workshop it only gets cutting to length and drilling. No welding touches it. Because the tube arrives galvanized and we remove material only at cuts and holes, the zinc layer stays intact along the full length, and the exposed steel needs only local touch-up. ASTM A780 lists zinc-rich paint as one accepted repair method, alongside zinc-based solder and zinc thermal spray.
Everything else: cold galvanized after welding
The remaining parts — brackets, joints, the carriage, frame elements — are cut, formed and welded in our workshop, then coated at ambient temperature with a zinc-rich coating. Some are electro-galvanized components we buy in. Both fall under the loose term cold galvanizing.
The engineering reason: coating integrity versus fabrication sequence
The coating has to follow the manufacturing route, not the other way round. The question is never which galvanizing is more advanced, but which process still delivers a continuous coating after the last operation that damages zinc. The main rail has no welding in its route, so it can be bought pre-galvanized and the coating survives everything we do to it. Hot-dipping a welded part means stripping zinc off the weld zone and repairing it, which lands back at cold-applied repair with distortion risk added.
Why we weld first and coat second
The industry position is that welding before galvanizing is better. Per galvanizeit.org, fabricating then hot-dip galvanizing gives complete coverage including the welds; the exception is a structure too large for the zinc kettle.
Welding destroys the zinc coating — here is how much
Welding through or beside galvanized steel burns off the zinc and contaminates the weld with it. AWS D19.0 requires zinc removal for 1–4 inches (2.5–10 cm) on both sides of the weld, on both faces, before welding. That is a wide band of coating lost per weld, and that loss — not the welding procedure — decides the fabrication route for welding galvanized steel.
450 °C will distort thin-wall tube and clog threads
Thin-wall sections carry the highest distortion risk in a 450 °C bath; plate and sections at or below about 1/4 inch (6.4 mm) are most exposed, and ASTM A384 sets out mitigation measures. A ladder lift frame is largely thin-wall tube. Molten zinc also does not drain cleanly out of a tapped hole, so threads block: usual practice is to galvanize a blank and tap afterwards, and internal threads below M8 generally need re-tapping. Welding also leaves heat-affected zones that can exceed 35 HRC, raising hydrogen-assisted cracking risk during immersion.
What that means for a part that must be welded
A cold-applied zinc-rich coating resolves all three at once: it goes on at ambient temperature after the weld is finished, with no thermal distortion and no thread blockage, and the same material repairs later damage. That is why our welded parts are cold galvanized — and why the main rail, which has no welding, is hot-dipped.
How to check galvanizing quality before you buy a ladder lift
Three checks catch most of the common problems.
The thickness gauge tells you more than the finish
A magnetic gauge cannot identify the process — it reads zinc, paint and zinc-rich coatings alike. It can tell you whether the number is plausible. Batch hot-dip should read at least 45–85 µm. If a supplier claims hot-dip and your gauge reads around 10 µm on a flat face away from welds, that is electro-galvanized.
Look at the cut ends and hole edges
Hot-dip coatings are thickest at edges and corners and coat the inside of hollow sections; painted coatings are thinnest there. Examine a cut end, a drilled hole and the tube bore. A hot-dipped tube is coated inside and out.
What spangle does and does not tell you
Spangle is the visible crystalline pattern on a hot-dip surface, a by-product of how the zinc froze, not an indicator of corrosion performance. A dull, dark grey finish often indicates a reactive steel that formed a thicker alloy layer, which is not a defect. Where appearance cannot settle it: EPR testing, or a cross-section micrograph showing the zinc-iron layers no other process produces.
Frequently asked questions
Is hot-dip galvanizing better than cold galvanizing?
For a bare steel part that will not be welded, hot-dip is generally more durable: thicker, metallurgically bonded, self-protecting at edges. For a thin-wall welded part, cold-applied zinc can be the better engineering choice, because the alternative damages the part during processing. "Better" only means something once the fabrication route is fixed.
Is your ladder lift fully hot-dip galvanized?
No. The main 40×60 mm square tube is hot-dip galvanized, bought already coated. The welded components are cold galvanized after welding. We would rather say that than let "galvanized ladder lift" imply one process across the machine.
Can a salt spray test prove how long the coating will last?
Not for hot-dip galvanizing. Per the American Galvanizers Association, ASTM B117 measures zinc metal corrosion rather than the protective layer, and runs without the wet-dry cycles that form it. Use coating thickness and the site's ISO 9223 category instead.
Which coating should I choose for a coastal site?
Thickness and edge integrity matter more than the process label. Surfaces directly exposed to onshore wind within about a mile of the coast can rust in 5–7 years even when galvanized. Specify the greatest thickness the standard allows and keep water from pooling in joints.
What happens if the zinc coating is damaged after welding?
It is repairable. ASTM A780 covers zinc-based solder, zinc thermal spray and zinc-rich paint, and on our welded parts the same production coating can be reapplied on site.
Choosing a ladder lift supplier who will tell you the truth about materials
The useful question is not "is it galvanized" but "which parts are which process, at what thickness". A supplier who answers in one sentence, with a standard number attached, usually knows their process route. One who says "all hot-dip" and cannot explain how the welds kept their coating has either not checked or is not saying. Check the welds, the cut ends and the tube bore. The solar panel lifting solutions range shows the configurations, including the sloped-roof solar panel lifter, the auto-turn solar panel lifter and the flat-roof solar panel lifter (manual flip). For alternatives to a lift altogether, see five ways installers lift panels to a roof. You can request a quote with your site height, roof type and load.
