This IM covers the requirements of zinc coating (galvanizing) by the hot dip process on iron and steel products made from rolled pressed and forged shapes, castings, plates, bars, and strips.


Also this IM covers the requirements for hot dip zinc coating and mechanically zinc deposited on fasteners and anchor bolts.


Galvanized Structural Steel, Miscellaneous Iron and Steel, Bolts, Nuts, Washers, Highway Lighting, Signing, and Signals, shall be furnished only from approved galvanizers identified in  the Office of Construction and Materials Approved Products Database (MAPLE) Materials Approved Products Listing Enterprise.



Galvanizers shall be approved prior to galvanizing any steel products or fabricated items for use on Iowa Department of Transportation projects.


Galvanizing companies seeking approval shall provide the Office of Construction and Materials the following information either in the Company’s written Quality Control Plan or as separate documentation:


1.       Name and location of the galvanizing plant


2.       Affiliation with the American Galvanizers Association


3.        Identification of any of the following ASTM specifications for which the galvanizing plant has routine experience:

       ASTM   A-53

       ASTM   A-123

       ASTM   B- 695

       ASTM   F-2329


4.       Galvanizing Tank(s) dimensions


5.       Molten Zinc

5.1.            Composition  (Percent by weight)

5.2.            Temperature Control and high / low temperature range

5.3.            Special Temperature Control for Compliance with ASTM F- 2329


6.       Preparation and Q/C procedures prior to galvanizing items


7.       Post-galvanizing treatments


8.       Post-galvanizing Q/C procedures

8.1.            Coating thickness measurement procedures

8.2.            Special inspection of surfaces for items intended to receive paint over galvanizing


9.       Preparation for Shipment with emphasis on protection of the galvanized coating during handling and transportation.


10.    Sample of the company’s galvanizing certification documentation

Note; The Iowa Department of Transportation does not accept certification to dual standards such as   ASTM A-153/ F2329.






1.     Steel and Iron – the grade, specification, designation type and degree of surface contamination of the iron or steel in articles and items to be galvanized shall be supplied by the fabricator to the galvanizer prior to the galvanizing process.

2.     Communication and / or consultation between the fabricator and galvanizer at appropriate stages in the fabrication process may reduce the occurrence of potential future problems.  Also communication between the fabricator, the galvanizer, and the paint shop shall be required to avoid the occurrence of potential future problems.


A travel log shall be required for every project with paint or powder coating over galvanizing and shall be initiated by the steel fabricator. 


A copy of the travel log is attached to IM 557, Appendix H.


The travel log shall accompany the fabricated items to be galvanized.  The galvanizer shall be required to complete the Galvanizer portion of the travel log and indicate the type of treatment (if any), that has been performed on the galvanized item, the date of galvanizing, signature and date.


No preparation or galvanizing of items to be painted or powder coated may be performed without a travel log from the steel fabricator.


Bath composition – the molten metal of galvanizing bath shall contain not less than an average value of 98% zinc by weight.

3.     Coating thickness

a.     Minimum of five test measurements on a specimen shall be taken.

b.     The average thickness of coating for all specimens tested shall conform to the requirements of ASTM A 123 for the specified categories and thickness.

c.      Coating thickness grade (as specified by ASTM A 123 and / or as specified in the contract documents.

4.     All sharp edges shall be rounded up (to near 1/16”) prior to galvanizing.

a.     Appearance – galvanized articles and / or items shall be free from uncoated areas, blisters, flux deposits, lumps, projections, globules (bubbles or tiny balls) and / or heavy deposits of zinc which will interfere with the intended use of the items, shall not be acceptable.

b.     High spots and rough edges such as the metal drip line shall be removed until it is level with the surrounding area, taking care that the base coating is not removed.

c.      Holes of ½” in diameter and larger shall be cleaned free from excess zinc.


5.               Thickness coating test – the thickness coating shall be determined by one or several methods

a.     Magnetic Thickness Gage (most common in the field and in the lab)

b.     Stripping method

c.      Weighing before and after galvanizing


6.               Certification

The galvanizer shall furnish certification to the Iowa Department of Transportation certifying that samples representing each lot have been either inspected and / or tested as required by the specification and also by ASTM A 123 and that the requirements of the ASTM and the Iowa DOT have been satisfied.


7.               Adherence

The zinc coating shall withstand handling consistent with the nature and thickness of the coatings and normal use of the items or article, without flaking or peeling which are grounds for rejection.


Zinc Coatings of Alloy Steel Bolts, Anchor Bolts, Nuts, Washers, and Special Threaded Fasteners:


Fasteners can only be galvanized by either of these two processes

a.     Mechanically galvanized ASTM B 695 Class 55 and/or galvanized to the requirements of ASTM F 2329.  This process requires the removal of excess zinc by spinning the parts in a centrifuge, or brushing the threaded portion or handling otherwise to remove the excess zinc.


The maximum temperature of hot bath cannot exceed 850º F. Galvanizing carried out at a temperature above 850º F can adversely affect the final mechanical properties of fasteners.  Therefore when galvanizing to the requirements of F 2329 the galvanizer shall provide a certified report indicating the hot zinc bath temperature and complete compliance with the ASTM requirements of F 2329.


b.     Dual zinc certifications such as A153/F2329 shall not be acceptable and shall be grounds for rejection.




1.     All threaded components (bolts, nuts, and anchor bolts) shall be coated by the same zinc coating process.  No mixed processes in a lot shall be allowed.

2.     Hot dip washers tend to bond to each other.  Delivered galvanized washers shall not be bonded to each other.  Bonded washers shall be rejected.

3.     The zinc coating on all type of fasteners shall be smooth and uniform in thickness.  The coated fasteners shall be free from uncoated areas, blisters, flux deposits, lumps, and any type of projections that would interfere with the intended use of the fasteners and /  or any defects not consistent with good galvanizing practice.

4.     The zinc coating thickness shall be uniform inside and outside of pipes, tubes, poles and/or certain tanks.  Inaccessible surface areas shall receive special attention from the galvanizer with surface preparation and zinc coatings.

5.     It is the responsibility of the galvanizer to ensure compliance with the specifications and the requirements of the ASTM (B695 Class 55, F2329 and A123).

6.     A chromate treatment is given to galvanized products which are used in fresh concrete to prevent a reaction between the galvanizing and the fresh Portland cement paste. The chromate treatment shall be performed immediately after the galvanizing process.




The galvanizer shall certify to the state of Iowa that the samples representing each lot have been tested and inspected as required by the intended specification and that the requirements have been met.  The galvanizer shall furnish on each shipment day a certified bill of materials or invoice, which identifies the county, project number, contractor’s name and the number of coated items. Additionally, the galvanizer shall report the average galvanizing temperature (when galvanizing fasteners is performed to the requirements of ASTM F 2329) and the average coating thickness of the production lot shall be furnished.


The certification of compliance shall be signed by a designated or responsible company representative and shall be stated as follows:


The materials itemized in this shipment are certified to be in compliance with the applicable ASTM Standards and the Iowa Department of Transportation Standard Specifications, IMs and meet the Buy America requirements as described in IM 107 for all steel, iron products and coatings.





Authorized Signature & Date



Articles and fasteners that are galvanized shall be protected from any damage to the coating, surface finish and appearance.


Fasteners shall be transported in weather tight containers


Bridge Components and Miscellaneous Items:


1.     Items shall be transported and stored under dry and well ventilated conditions to avoid wet storage staining.

2.     When stored outdoors or transported, surface to surface contact between items shall be avoided with suitable packing material between galvanized items.

3.     When stored outside, items shall be stored off the ground and when possible, at a slight angle to allow water to run off.

4.     Suitable packing shall be placed between layers of stacked or bundled galvanized items.

5.     Suitable packing materials may be foam padding, foam wrap, carpet or cardboard. It shall be placed between layers of stacked or bundled items before binding them together