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

• 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

• 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

• 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

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