I am an Architect

Should I specify galvanising?

I am an Engineer

What are the design concerns?

I am a Steel Fabricator

What turnaround will I get?

I am a Farmer

How much money will I save?

Want the best possible finish on your galvanized steel work?

Well designed steelwork lends itself to a smooth clean finish when galvanized. The first question you should ask yourself is: ‘How suitable is this article for dipping in a bath of molten zinc?’

Areas for consideration:

Venting & Drainage

You must allow for the free flow of molten zinc throughout your fabrication. Every enclosed section or overlapping plate must have adequate holes.

  • No hole should be less than 10mm
  • Preferred minimum hole is 12mm
  • For hollow sections the absolute minimum hole diameters are as follows:
Diameter width of hollow section (mm)Minimum size of hole (mm)
>25 to 5012
>50 to 10016
>100 to 15020
>150Consult Sperrin
  • Holes should be located at the ends of hollow sections arranged in diagonally opposite pairs
  • The method of suspension of the fabrication (see below) should be borne in mind when preparing holes.
  • The preferred method is to crop, punch or drill holes
  • Concealed / internal venting is not acceptable


Poor quality castings may absorb process fluids that will hinder the galvanizing process. Always check with your supplier that you are getting mild steel castings that are suitable for hot dip galvanizing.

Dissimilar Steel

As hot dip galvanizing is an alloying process it draws out the varying components of the individual piece of steel. This can result in significant colour variations between round bar and box section or between channel and tubing.


There can also be an issue if you combine light and heavy sections. These will be dipped at 450 C and will cool down at different rates. This may cause them to pull against one another.


Pinholes in welds may also absorb process fluids and hinder the galvanizing process.These may leak out after galvanizing and form a brown stain on your steel. This is easily removed and will not recur. If you would like advice on any aspect of design, please phone us or send us a drawing of the item you would like to dip. This often allows us to recommend some simple alterations that will provide you with the optimum finish.

design for galvanising sperrin

Early consultation between galvanizer, fabricator and designer is the key to obtaining the best results from the galvanizing process. Design features, which may aid the access and drainage of molten zinc, will improve the quality and appearance of the coating. Download our Design for Galvanising guide

If there is anything you have ever wanted to know about metal finishing processes, as well as how to prepare and treat your metal projects before delivering them to a galvanizing plant, click on the links below or contact our Technical Support Team.


At Sperrin Galvanisers, our highest priority is providing you unmatched service and support. Please contact our team, and we’ll be in touch as soon as possible.

Sperrin Galvanisers Draperstown

Jim McErlean

Technical Sales Representative

tel: + 44 28 796 27657
email: jim.mcerlean@sperringalvanisers.com

Michéal Murray Sperrin

Sperrin Galvanisers Tynagh

Michéal Murray

Technical Sales Representative

tel: + 353 87 414 98 69
email: micheal.murray@sperringalvanisers.com