Since this thread was originally about shop primers, how about the same questions for them?
Going back to Brett’s original post -
APWA/AASHTO ‘Standard Specifications’ (which accounts for a LOT of structural steel) indicates: “All material classified as structural steel shall be painted with a shop applied, inorganic zinc silicate primer, followed by a field applied two coat paint system…”.
There are two methods - A & B: Method A is an epoxy second coat with an aliphatic urethane topcoat; Method B is a low ambient temperature system (down to 35 degrees F). Method B, I believe, accepts those moisture-curing characteristics of ‘newer’ polymer coating systems.
Also: “Terminology used herein is in accordance with the definitions used in Volume 2, Systems and Specifications of the SSPC Steel Structures Painting Manual, current edition.” (current = Volume 2, 2005 Edition).
I consider that APWA/AASHTO spec “the authority” because it is applicable to nearly every structural steel bridge in the US.
Lynn, was your seminar in San Francisco? If so, I think I was at the same one.
What I got out of my seminar yesterday was that there are a lot of coating and preparation standards that we can use to get good performance, but “people don’t do what you expect, they do what you inspect.” Field (or shop) inspection is the way to be sure you’re getting what you asked for. The presenter recommends PDCA standard P2-04 for third party inspectors, and some NACE standard I can’t find right now for the method of inspection.
Susan, I think shop priming should be specified by characteristics, recognizing that a shop probably has products they’re comfortable and successful with. As for VOC limits on shop primers, I’m not imposing them for this particular project, but I remain personally curious (for the good of the world) about the typical VOC content of what I’m specifying. Now, if I could just find that NACE recommended practice…
Vivian, Would that it had been so - I’d like to spend more time in San Francisco! No, my seminar was put on by my local CSI chapter and was held at the county zoo. It concerned coatings in general, but one 45 minute session was on priming and sealing. The presenter spoke of organic zinc rich primer, inorganic zinc rich primer, wash coat primers, etc. He stressed that “shop coat” is not good enough and suggested that we add minimum surface preparation requirements, call for a single component primer with rust inhibitor, watch for a short dry-time (time is money for the shop and if it’s too long, they won’t do it), and check into cost.
Galvanizing isn’t necessarily the best process to treat steel, especially that which will be coated in the field.
A wash primer should be no more than 1 to 1-1/2 mils thick to enhance adhesion. More than that will crack.
Organic zinc rich primer (83% zinc) provides particle to particle galvanic protection. Inorganic zinc rich primers are useful for high tempreature situations and can be stand-alone, but are not recommended in high alkali or high acid situations.
Moisture cure primers are good in wet climates or immersion situations.
100% solids epoxy primers are useful for CMU, precast and concrete.
And if the steel will be fire-retardant treated, you need a totally different kind of primer. Talk to the Tnemec rep in your area.
So it’s important to know what you’re priming, where and how it will used and treated on the job site, and what’s going to happen to it afterwards.
Hope this helps.
Lynn