Zinc Wire Applications: Arc Spray, Flame Spray and Where the Coating Actually Fails

Updated 9 September 2026 · 11 min read · All calculations shown, inputs stated

What the standard actually covers

Commercial thermal spray zinc wire is made to ASTM B833, currently B833-20, "Standard Specification for Zinc and Zinc Alloy Wire for Thermal Spraying (Metallizing) for the Corrosion Protection of Steel". Three clauses matter to a buyer and almost nobody reads them.

First, the base metal must be either special high grade zinc (Z13001) or high grade zinc (Z15001). That is where the 99.99-odd percent purity floor comes from - it is not a marketing number, it is a designation in the standard.

Second, the wire must be clean and free of corrosion, adhering foreign material, scale, seams, nicks, burrs, bends or kinks that would interfere with the spray equipment. This is the clause that matters most in practice and the one most often quietly violated. A kink does not show up on a chemistry certificate; it shows up as a gun stoppage at height on a bridge.

Third, it must uncoil readily and be a continuous length per spool, coil or drum. Splices and welds are permitted provided they do not interfere with the equipment. So a splice is not a defect per se - but a splice that jams your feed rollers is, and the standard puts the burden on demonstrating it does not.

The number nobody publishes: metres per kilogram

Wire is sold by weight and consumed by length. Every planning question - how many spools, how often you change them, how long a drum lasts - needs the conversion, and it depends only on diameter and density.

Zn density                      rho = 7.14 g/cm3
Cross-section of diameter d     A = pi * (d/2)^2
Mass per metre                  m = A * rho
Metres per kilogram             1000 / m

d = 1.6 mm ->  A = pi * (0.08 cm)^2 = 0.02011 cm2
               m = 0.02011 * 7.14   = 0.1436 g/cm = 14.36 g/m
               1 kg = 1000 / 14.36  = 69.7 m

Now use it. A twin wire arc gun running 1.6 mm wire at a total of 25 kg per hour is consuming 12.5 kg per hour on each of its two wires. Each wire therefore runs at 12.5 × 69.7 = 871 metres per hour, or 14.5 metres per minute, and a 20 kg spool lasts 1.6 hours. Two spools per gun, changed roughly every hour and a half.

That is the calculation that sets how many spools go up the scaffold. It is also why drum-packed coil exists: a 250 kg drum of 1.6 mm wire holds 17,425 metres, which is the difference between a shift and a week.

Coverage: square metres per kilogram

1 kg zinc                    = 1000 / 7.14 = 140.06 cm3
At thickness t, zero loss    area = 140.06 cm3 / t

t = 100 um = 0.0100 cm  ->   14,006 cm2 = 1.401 m2/kg
t = 150 um = 0.0150 cm  ->    9,337 cm2 = 0.934 m2/kg
t = 200 um = 0.0200 cm  ->    7,003 cm2 = 0.700 m2/kg

Apply deposition efficiency (DE). Arc spray on flat work
typically 60-70 %; corners, edges and round work less.

DE 65 %:  100 um -> 0.910 m2/kg
          150 um -> 0.607 m2/kg
          200 um -> 0.455 m2/kg

Three jobs, worked

1. A bridge girder, 1,000 m² at 150 µm

Take flat plate work with reasonable access, so 65 percent deposition efficiency is fair. From the table, 0.607 m²/kg, so 1,000 m² needs 1,648 kg. Add 5 percent for start-stop, spool ends and the material you will lose masking edges and you are ordering 1,730 kg.

At September 2026 pricing - LME cash 4,157 plus 400 conversion, so 4,557 per tonne - that is USD 7,884 of wire, or USD 7.88 per square metre of coated surface. Move the conversion premium to 500 and it becomes USD 8.06 per m². Move zinc by 10 percent and it moves about 9.1 percent.

2. Ductile iron pipe, external zinc coating

Pipe is round and rotates, which changes the efficiency picture: overspray that misses a flat plate is partly recovered on the far side of a spinning pipe, so real efficiency on a dedicated pipe line runs higher than on structural steelwork. The coating is also much thinner - the metallized zinc layer on ductile iron pipe is a thin sacrificial layer, generally well under 100 µm, over which a bituminous or synthetic topcoat is applied.

The arithmetic follows the same table. At 60 µm, theoretical coverage is 2.334 m²/kg; at 70 percent efficiency that is 1.634 m²/kg. Do the job backwards from the specified minimum average and add the usual allowance for the pipe ends.

What actually drives wire choice here is continuity of feed, not metallurgy. A pipe line running continuously punishes spool changes, which is why this application favours drum-packed coil over spools, and why pay-off behaviour matters more than tensile strength.

3. Capacitor end-spray

Arc spray zinc is also used to metallize the ends of wound metallized film capacitors, producing the contact layer the leads are soldered to. This is a completely different purchasing problem: the tonnage is trivial and the consistency requirement is brutal.

Here you want fine wire - 1.3 mm or 1.6 mm - at the top of the purity range, because dross and surface oxide project onto a component that has to make electrical contact. You also care about lot-to-lot consistency more than price, because a spray parameter set qualified on one heat of wire may not transfer to the next. Buy more, of fewer lots, against a retained sample.

Pure zinc, or 85/15 zinc-aluminium?

This is the question that comes up most, and the economics are usually done wrong. People compare price per kilogram. They should compare price per square metre covered.

Pure Zn                       rho = 7.14 g/cm3
Aluminium                     rho = 2.70 g/cm3
Zn-Al 85/15 (rule of mixtures, inverse):
  rho = 1 / (0.85/7.14 + 0.15/2.70) = 5.73 g/cm3

Volume per kilogram:
  pure Zn    1000 / 7.14 = 140.06 cm3
  85/15      1000 / 5.73 = 174.60 cm3

Coverage advantage of 85/15 at equal thickness:
  174.60 / 140.06 = 1.247  ->  +24.7 % more area per kg

So the break-even is clean: if 85/15 wire costs less than about 25 percent more per kilogram than pure zinc wire, it is cheaper per square metre laid down. Above that, pure zinc wins on material cost alone, and you buy the alloy for its performance rather than its economics - better abrasion resistance, better behaviour in industrial and marine atmospheres, and a coating that tolerates higher temperatures.

Four jobs where zinc wire is the wrong answer

We would rather lose an enquiry than sell into a failure, so here is where we say no.

Two things we are deliberately not giving you

We are not giving a bond-strength figure. Published values exist, but bond strength in thermal spray is dominated by surface preparation - blast standard, anchor profile, cleanliness, time-to-spray, dew point - and quoting a laboratory number into a field specification gives false confidence. Ask your applicator for pull-off test results on your prepared substrate.

We are also not giving a service-life-to-first-maintenance table. Zinc coating life depends on the actual atmospheric corrosivity category at the site, coating thickness, sealer and topcoat. Any single number you see quoted without those inputs is marketing. Derive life from your own site category and specify thickness accordingly.