By Brian Farrell
Now that you have chosen the proper length for your application as described in Part 1 of this series, you now need to determine the proper type of fastener based upon the application. Carbon steel or stainless steel, painted or non-painted, capped head or molded head, washered or non-washered. The application will provide you the proper answer to each one of these choices as long as you know the differences.
Fasteners are produced from either carbon steel or stainless steel. The majority of the fasteners used in buildings and roofing are carbon steel, due to its hardness and strength. This also the material of choice for self-drillers. Carbon steel, however, will quickly corrode when exposed to the elements, unless coated with at least .7mils of zinc coating. The alternative, which is normally described as a Series 300 stainless steel fastener is very corrosion resistant but is intrinsically a softer material and does not lend itself well to self-drilling fasteners unless heat-treated to increase the hardness. It can, however, be used in a self-tapping application. A heat treated stainless fastener is a Series 410 and is capable of drilling and tapping material similar to a carbon steel fastener. Some heat treating processes can result in a 410 stainless steel fastener that can be prone to rust depending upon the environment. It is recommended that 410 stainless should be plated or coated to minimize rusting. The ultimate solution would be a Series 300 fastener for corrosion resistance with the drilling capabilities of carbon steel.
The fastener manufacturers have addressed the corrosion issue by developing various types of alternatives. One of the first fasteners on the market and one that is still popular today is a carbon steel fastener with a Series 300 stainless steel cap and an integrated EPDM washer. This fastener combines the best of both, a carbon steel fastener for drilling and a 5/16” stainless steel cap for corrosion resistance and longevity. Excellent for use with long life panel coatings such as Galvalume®, generically known as an AZ-55, AZ-50 coating.
A second type of corrosion resistant fastener is also a “capped” fastener but the cap is molded to the fastener head. This fastener also has a carbon steel body with a 3/8” or 5/16” molded or cast cap made from zinc/aluminum with an integral washer. It has several trade names in the marketplace but its look is unmistakable. To some it is not as aesthetically pleasing as the stainless steel cap but it is just as effective for use on long life panels.
Another type of corrosion resistant long life fastener is more of a hybrid, combining the Series 300 stainless characteristics with a carbon steel drill point. The 5/16 HWH fastener head and body are made from Series 300 stainless steel, but it has a welded carbon steel drill point. In comparison to the aforementioned “capped” fasteners, these are relatively new but may be just as effective.
Fastener life is critical and needs to match or exceed the life of the panel on which it is being used. All the manufacturers have various types of platings, coatings, paints, and methods for applying them. The most popular plating for carbon steel fasteners and one that has been around for many years is zinc with a chromate topcoat. This plating is fine for internal use and as a base layer for a painted fastener but when exposed to the elements, it will corrode quickly.
There is, however, a coating available for carbon steel fasteners that offers significant long term protection from the elements. It is normally dull silver or gray in color and has various trade names many of which end in “seal”. To name a few we have Climaseal®, Oxyseal®, TRI-SEAL®, and many others. As indicated by the name, this is a sealer coat of material that allows the fasteners to be used as is or it acts as a base layer to a paint system. The type of material used in this coating and the number of coats is dependent upon the manufacturer. Some manufacturers use a two coat system and some use a three coat system. It appears, however, that from test results, they are all similar in their ability to withstand harsh conditions and protect the fastener from corroding. It is not comparable to the life or corrosion resistance of a stainless steel fastener but again, based upon test results, it is at least 20 times better than an uncoated or plated carbon steel fastener.
As a guideline, the sealed or coated fastener can be used everywhere a long life fastener is required with the exception of highly corrosive applications and marine or coastal environments. In those applications, a stainless steel or zinc/aluminum fastener is required.
In today’s world of color, rarely is a stainless steel or long life coated fastener acceptable without being painted. Every fastener supplier offers the most popular colors used by both building and panel manufacturers as well as the ability to quickly match special colors. There are two methods currently used to paint fasteners, the tried and true spray painting method and the more technologically advanced powder coating. Although powder coating will provide a tougher more durable finish, either method, properly applied, will result in an acceptable finished part, which is what matters in the field.
For painted fasteners used in conjunction with the standard modified siliconized polyester paint finishes, you want a fastener with a life that will correspond with the finish warranty period on the panel. Your fastener supplier can provide assistance in choosing the proper coating system to match the warranty period. For applications with long life paint finishes such as Kynar®, it is best to use a painted stainless steel or zinc/aluminum capped fastener. These are both long life fasteners and will last as long as the panel finish warranty. The alternative would be to use a fastener with one of the previously mentioned sealer coats as a base to the final paint system. Again, your fastener supplier can provide you guidance in matching the painted fastener longevity to the length of your finish warranty.
The cost of the fastener is small part of the total cost of the panels and an even smaller part of the total cost of a metal building. It is, however, a very significant part of the finished product. The failure of that very small and relatively inexpensive part can result in monumental and costly issues years later.
Choose your fastener carefully as your roof panel, wall panel, or building performance depends on it.
(The author would like to thank Marty Martin and Joe Stager of Triangle Fasteners for their assistance in proofing the article.)