Let me start by quickly explaining that one should ABSOLUTELY NOT try to compare an after-fabrication hot dip galvanized coating to pre-galvanized items such as sheet metal, flashings, pre-galv tubing, EMT, fasteners, furniture, magazine racks, etc…  These items are galvanized in a different manner, and in tightly controlled, product specific factories.  This results in:

1. a much smoother finish, and
2. a much thinner coating.

These items will look much smoother when new, but will fail in service much, much sooner than a standard after-fabrication hot dip galvanized item.

It is also important to understand a bit of how hot dip galvanizing works.  In brief, an article to be hot dip galvanized is dipped into a vat of 840-degree molten zinc metal.  This is not a water solution of metal ions as in plating, but the actual metal itself, heated up until it melts in to a thick, heavy, viscous liquid.

When the part is submerged in the galvanizing bath, it undergoes a metallurgical alloying reaction with the galvanizer’s zinc.  Simply stated, some steels will react with the same zinc bath differently due to differences in the chemical composition of the steel.  This can create differences in surface color and texture/smoothness between different parts, between different sections on the same part, and even between different areas on the same section of a single part.

Then during withdraw from the galvanizing bath, the molten zinc must run off the surface of the part as it leaves the bath, creating the final surface texture.  During the withdrawal phase, the design of the part, the speed of withdrawal, the angle of withdrawal, the ventilation and drainage holes, among other factors all influence the final surface appearance.  Combined with the fact that thick, heavy molten zinc metal simply does not want to drain easily form the surface of a part, you can see the difficulty in obtaining a high degree of smoothness.

As you can see, the surface appearance, coloration, and relative smoothness are all influenced by many factors.  Many of these can not be controlled by the galvanizer, and of those that can not, some are beyond the control of the fabricator.  What this means is that there are no easy guarantees on the exact surface appearance, color, or smoothness of an after fabrication hot dip galvanized coating.

We do guarantee that the product we galvanize conforms to current commercial standards, as well as to ASTM A-123, the standard specification for after-fabrication hot-dip galvanizing.  Within this specification, there are tolerances for color, appearance, and smoothness due to factors beyond control.

I like to summarize this topic by likening an after-fabrication hot dip galvanized coating to a big gruff, rough, tough guy.  Our coating is the strongest, longest lasting, most durable, look rust in the face and laugh coating.  There is nothing else on the market that can come close to the durability of our coating in almost any environment on Earth.  That being said, I did include the adjective “gruff.”  An after-fabrication hot dip galvanized coating will be loyal to you always, but it can at times be rough, bumpy, runny, pimply, and, well… gruff.

The good news is that this rough and tumble coating will stay rough and tumble… and rust free for decades to follow.  It that time, all of the other smooth, pretty coatings will all have been repaired, repainted or replaced several times over.

This being said, we pride ourselves in providing the best quality hot dip galvanized coatings possible.  We always strive to give you product that is as smooth and clean as possible.  With appropriate expectations, and with our unique hand cleaning process after galvanizing, you are sure to be pleased with the results!

We get calls periodically from fabricators or end users asking if they can request a certain color or shade in the galvanizing color. We also get calls from fabricators asking why their steel came out a certain color today, when the load they galvanized the week prior came out a different color. The truth of the matter is that the galvanizer has very little control over the exact finish color. Please let me explain.

The production of a galvanized coating has as its basis a metallurgical reaction between your steel and the molten zinc in our galvanizing bath. This reaction results in the formation of several iron-zinc alloy layers (dark), with normally a pure zinc outer layer (bright silver). Certain elements found in steel (mainly silicon, phosphorous, carbon, and manganese) can dramatically affect the alloying reaction between steel and molten zinc. If the reaction rate is increased or is allowed to continue at lower temperatures during the cooling down period, a small percentage of iron (approx. 0.5% Fe) can be drawn from the steel to the surface of the coating. This results in the darker, more matte, or sometimes even a spider web like finishes.

It is common for an article to have adjacent areas of bright and dark colors, which will correspond to differences in the relative concentrations of the elements listed above and/or slightly different cooling rates. Basically, the steel in the darker areas has levels of certain elements that are out of range to produce a bright silver coating. You may notice brighter coatings around edges or bolt-holes, with a darker color in between where cooling was slower.

This effect is normal for higher reactive steels, and is not a detriment to the life-span of the coating. In fact, the darker areas, since they are indicative of higher reactive steels, often have a thicker coating than a brighter colored area. Thus, they will last longer. Thicker coatings can be more brittle than standard coatings, so extra care in handling and installation is advised.

Interestingly, everything that gets galvanized comes out bright shiny silver… at first. When items turn darker or matte gray, this happens while the part is suspended in the air, cooling. We certainly hope that everything stays bright and shiny; but every galvanizer, on occasion, has to helplessly watch freshly galvanized product turn dark in front of their eyes, just hanging there.

Holes should always be as close to the end of the pipe or tube as possible, and never more than 1” from the end.

Holes should always be as close to the end of the pipe or tube as possible, and never more than 1” from the end.

Due to the nature of cast iron galvanizing, it is recommended that any cast iron pieces be sandblasted before processing to achieve the best possible finish. Cast iron often contains scrap iron, and as a result, the chemistry of the metal is unpredictable. Also, casting residues embedded in the pores of the metal are not cleaned during chemical cleaning, and can result in uneven galvanizing and bare spots. It is best to choose the least porus cast iron possible. Sandblasting helps to remove impurities from the cast iron surface, giving it a more consistent finish.

If the thread is to be chased after galvanizing by heating and wire brushing, it is best to either leave the thread as-is, or over-tap the thread by 0.003 inches in diameter.  This cleaning method will remove nearly all of the galvanized coating.  This is the most common method for handling threads, especially when a threaded stud is welded onto a fabricated assembly.

Another method is to over-tap the thread before galvanizing, and then re-tap to the correct size after galvanizing.  This will provide the most corrosion resistant product possible.  Please follow this table for over-tapping dimensions.

Galvanizing is a very specialized process resulting in the absolute longest lasting coating for your steel products. However, since the galvanizing process involves submersion of your product into a molten zinc metal bath at about 840 degrees F, there are some potential drawbacks. One of these is heat related expansion that may result in warping of your product.

All material that is galvanized goes through some degree of heat expansion. The degree of expansion varies, according to a number of factors. The main factors are material thickness and the ratio of surface area to mass. In plain English, thinner materials tend to expand more than thicker, more robust materials.

The most common type of heat related warpage is with solid sheet material, perforated plate, wire mesh, and expanded metal. These all have a high surface area to mass and will expand quite a lot at galvanizing temperature. If these materials are done in loose sheets, their expansion and contraction will go unnoticed. However, if the sheeting is welded into an assembly that is more rigid (and will have less heat expansion), then the greater heat expansion of the sheeting may result in permanent warping and twisting.

Also, galvanizing items that are asymmetrical, such as plain channel iron, or a gate that has the pickets off-set to one face, may result in the item curving to one side.

Fabrication methods can also induce a tendency for material to warp. Remember that the heat of galvanizing is a great stress reliever.
• If an assembly is welded all on one side, then flipped over and welded all on the other side, this may induce stress in the assembly that will result in warpage during galvanizing. Think of it this way… if you had to brace it or secure it to keep it from moving while you welded it, it will likely move during galvanizing.
• Having many cutouts in thinner materials can also leave stress behind in the metal that will be relieved during galvanizing, resulting in unwanted warping.

Just how much can steel expand during galvanizing you ask? We tested it to give you a real world example. A piece of 1.5” standard pipe at 21’ long will expand approximately 1.5” during galvanizing. That’s a LOT! Take warpage seriously so you won’t be disappointed!