Do you have a metal decking job and do not understand the finish that is specified on the plans? In this article, we will discuss the different finishes and when it’s best to use each of them. The four finishes we will review are:
- Galvanized
- Galvanized and prime painted
- Prime painted gray
- Phosphatized and prime painted
Galvanized Metal Decking
Galvanized metal decking is the most common type of metal deck.
It is the standard for nearly all metal floor deck jobs. It is also common for metal roof deck projects.
The main advantage of galvanized is that a finished coat of paint does not need to be applied to the metal decking. It is also recommended in high moisture or corrosive environments.
There are two types of galvanized metal decking:
1. Galvanized G60 Metal Deck
G60 is a specification for hot dip galvanizing. It means that there will be .6 oz total weight of zinc per square foot. G60 is the most common type of galvanized metal decking. It is used on more than 90 percent of metal deck jobs that are specified as galvanized.
Availability for galvanized G60 metal decking - Most metal deck distributors have a large selection of panels and gauges in this finish. They are available for immediate pick up on the smaller projects. Larger projects typically have a 2-3 week lead time.
2. Galvanized G90 Metal Deck
G90 is a specification for hot dip galvanizing. It means that there will be .9 oz total weight of zinc per square foot. G90 galvanized metal decking is rarely specified on a job. It would be useful in a corrosive environment such as a project that is close to the ocean.
Availability for galvanized G90 metal decking - It will be difficult to find G90 with immediate availability. Metaldeck.com has 18 gauge G90 “ B “ roof deck in stock. You can try your local metal decking distributor, but it is doubtful you will find G90 in stock. Larger projects typically have a 3-5 week lead time.
Galvanized and prime painted
This type of metal decking is not used often. This specification arises when you have a project that has a long span condition, is exposed to the weather, and needs an architectural paint finish. Metal decking cannot be ordered with an architectural paint finish. Instead, it needs to be painted in the field. It is much easier to do so when the metal deck arrives with a factory primer coat.
Problems with using galvanized AND prime painted metal decking
- Availability for galvanized and prime painted - It will be difficult to find this material with an immediate availability. There will be order minimums which will vary from supplier to supplier. The typical lead time will be 3-5 weeks.
Prime painted gray metal decking
Metal decking in a gray prime painted finish is most commonly used in applications where the metal deck is not exposed. The most common application is B deck or HSB-36 with a built up roof installed on top of the metal decking.
The main advantage with prime painted B deck is a cost savings of about ten cents per square foot. The main disadvantage is if the material is left exposed to the weather it will get red rust stains on the top and bottom of the panel.
Availability for prime painted metal decking - The availability of the product varies from state to state. If you live in a state such as Arizona that has a steel mill that both manufactures and paints metal decking than it will be readily available. Otherwise it will either not be available or there will be added freight charges. Smaller projects range from immediate availability to not available at all based upon the location of the project. Larger projects typically have a 3-5 week lead time.
Phosphatized and painted metal decking
This is metal decking in which the top of the deck is not galvanized or painted. The bottom of the material will have a prime painted finish. Metal deck with this specification will be used as a 1.5”, 2”, or 3” deep floor deck. However, you cannot paint the top of the metal decking because the paint will prevent a chemical bond with the concrete.
The purpose of this material is that the cost of bare cold rolled steel and primer is cheaper than galvanized. On a small job the price difference would be negligible. It would have to be a project of substantial size such as a high rise building for there to be worthwhile cost savings.
When phosphatized and prime painted material is used it will nearly certainly lead to ugly red rust stains at the bottom of the panels. If the underside of this material is exposed this will be a problem and a finished paint should be applied to prevent this.
- Availability for phosphatized and painted metal decking - It will be difficult to find phosphatized and painted with immediate availability. There will be order minimums which will vary from supplier to supplier. The typical lead time will be 3-5 weeks.
Nearly all floor deck jobs are specified as a G60 galvanized. Roof deck jobs normally are G60 or gray prime painted. Rarely will you see the other finishes. It is important to always use galvanized if the top or bottom of the panel will be exposed to the weather. Otherwise you will end up with ugly red rust streaks on the panel. Fortunately, there are not a lot of options and in most cases the engineer will be the one that decides which finish is best.
Metaldeck.com has an extensive steel deck inventory that includes prime painted gray, galvanized G60 and G90. If the product is not in stock we will order it for you. Delivery is available anywhere on one of our route trucks. We can ship you metal decking quickly and inexpensively.
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