Galvanizing vs. Paint Systems
While some people may have the misconception that zinc-rich paint provides the same level of protection as hot-dip galvanizing, there is little comparison in terms of corrosion performance, sustainability and lifespan.
The below charts outline the measurable and significant benefits of hot-dip galvanizing versus inorganic zinc-rich paint.
Requirements / Characteristics |
Hot-Dip Galvanized Steel |
Inorganic Zinc-Rich Paint |
Special Handling |
No |
Paper interleave, cloth slings, wood separators |
Field Touch-Up |
No |
Required |
Application |
Factory |
Field or factory |
Weather Dependent |
No |
Yes |
Temperature Range |
-75F to 392F |
<200F |
Corrosion Protection |
Cathodic & barrier |
Barrier |
Hardness/Abrasion Resistance |
179 to 250 DPN |
Varies by type |
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Service Life/Durability (a)
Requirements / Characteristics |
Hot-Dip Galvanized Steel |
Inorganic Zinc-Rich Paint |
Rural |
>100 years (b) |
27 years (c) |
Urban |
90 years |
17 years |
Industrial |
70 years |
12 years |
Marine |
50 years |
12 years |
(a) To 5% rust on substrate steel
(b) Zinc Coating Life Predictor, Zhang, 2001
(c) NACE Paper 06318, Helsel, Melampy, Wissmar, 2006
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Coating
Requirements / Characteristics |
Hot-Dip Galvanized Steel |
Inorganic Zinc-Rich Paint |
Thickness |
Exceeds ASTM A 123 minimum (> 3.9 mils for 1/4” thick steel) |
Variable - may not meet required minimum due to lack of skill |
Coverage |
Exterior & Interior |
Exterior surfaces only |
Consistency |
Edge & Corner thickness ≥ flat surfaces |
Edge & Corner thickness < flat surfaces |
Cathodic Protection |
Zinc metal is anodic to steel |
Maybe - Zinc % may be too low for conductivity/Binding materials may not be conductive, minimizing cathodic protection |
2000 Hour Immersion Test |
No base steel corrosion |
Paint absorbed water & underfilm corrosion of the substrate steel occurred |
Ultraviolet Ray Exposure |
No effect on performance |
No severe degradation |
Abrasion Resistance |
Alloy layers are harder than base steel (DPN hardness ranging from 179 - 250) |
Moderate; DPN hardness approximately 33% less than HDG |
Performance Range Testing |
-100 C to 350 C |
Deterioration at 250 C |
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Application
Requirements / Characteristics |
Hot-Dip Galvanized Steel |
Inorganic Zinc-Rich Paint |
Surface Preparation |
Documented, timed, scientific sequence |
Function of human expertise, intolerant of improper cleaning/profiling |
Procedure |
Observable completion of metallurgical reaction |
Constant agitation of mixture, regulation thickness & drying time per pass |
Application |
24/7/365 - all weather |
Requires specific temperature conditions |
Bond Strength to Steel |
~ 3600 psi |
~ 600 psi |
Size Range of Products |
90’ - 120’ long by 6’ - 8’ wide/deep |
Unlimited |
The American Galvanizing Association, “Hot-Dip Galvanized Steel vs. Zinc-Rich Paint”, www.galvanizeit.org