Over the past 18 plus years in the metal roofing roofing industry I have pretty much seen everything when it comes to specifications. The reality is as an architect has to pick 3000 (on average) products per project and we as manufacturers look to use “Spec Hooks” to make our products different from our competitors. Therein lies the issue. Spec Hooks can cost your owner more money for the same result. Here’s an example; your metal roofing resource comes in to your firm and promotes a metal roof system with a “three coat” or “increased gauge” stating better long term performance. It would make sense…its roofing and thicker is probably better…40 mil rubber vs. 60 or 80 mil rubber provides a longer and more stable performance however added thickness to paint film doesn’t enhance performance unless it’s color or environment based.
Let me explain the anatomy of a paint system. A standard paint system used in our industry is a two coat paint system consisting of a pretreatment, primer and topcoat. The pretreatment preps the strip of aluminum or steel to accept the primer (0.2mils to 0.3 mils of primer) and then the PVDF topcoat (0.7mils to 0.8mils) is applied which is typically a Kynar 500 or Hylar 5000 for commercial projects. The system is passed through the paint line once we are left with a baked-on 1.0mil DFT (Dry Film Thickness) to standup to the elements. The paint system warranty (typically 20 to 35 years depending on the manufacturer) is backed by the paint company and is passed through the Coater to the end-user (manufacturer) and covers color fade, chalk and delamination.
So if the standard paint system offers you this level of performance and warranty when should you spec a three coat? If you plan on using a VIVID color like a bright red, bright yellow, bright blue, purples and oranges then you should add the additional protection of a clear coating on top of the topcoat. This clear coat aids for long term performance of the vivid and unstable pigments that make up this vivid color which in the past we lead-based pigment (no longer being used). If you choose a standard Bronze or Green, there is no need use a three coat as it will not improve the long term performance based on the warranty term. A three coat has to go through the paint line twice which adds cost and increases the scrap amount of the paint run and can add up to 40% to the total cost of your roof installed system. It’s just not worth it for your owner and is not a “belt and suspender” approach but a sales tool to make you think that thicker is better. Another reason to use three coats would be to enhance environmental performance however you should consider that if you are installing a metal roofing in aggressive environments that you need to be more concerned with the core substrate of the products rather than it’s paint system. Here’s a simple way to look at paint….paint doesn’t rust and just like on the interior it adds character and color and although its a coating its not a protective coating against red rust. So…let’s make sure the product will perform in its intended environment first and then select your paint system. Aluminum is the better substrate and choice for aggressive environments. Increasing the gauge of the steel product, unless you are concerned about deflection (oil canning), doesn’t add any additional corrosion resistance. Increasing the gauge from 24 gauge to 22 gauge can add up to 20% to the overall cost to the installed project. Going with aluminum adds 30% compared to 24 gauge but is the better solution for aggressive environments.
The perception that thicker is better works well for underlayment and other types of roofing but is a tricky “Spec Hook” and adds very little value and a lot of costs for your owner.