I’m building an elevated concrete deck, which is supported by a couple of W8x13 I-beams. The I-beams will be protected from the elements except for the warm, humid, coastal South Carolina air that floats in from the sides. Rather than paying the extra $600 for Galvanized I-beams I figured I could paint them. Can anyone recommend a good paint/primer that would do the trick?
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These need to function long term, with miimal future maintenance. I'd recommend the galvanizing.
Your only other options are catalyzed paints, which will probably cost as much or more than the galvanizing.
Go to a good paint store near you and ask for recommendations.
Powder coating would be on the top of my list - it's probably the most durable other than galvanized finishes.
If you are sold on paint, I'd look at the more expensive paints primarily used for automotive rustproofing - they are over $100 a gallon, but last well if the metal is well prepped. PR15 is what many of us use on our car frames and it works really well. It's a one part polyurethane, perhaps no better than the two part polyurethane industrial paints, but it's readily available and it has a good track record. Google pr15 and the company has easy to understand guidelines for what you're doing.
I will warn you about one thing - don't paint out of the can if you want to reseal it - any paint around the rim will permanently join the lid to the can and you'll destroy them both to get the lid off again. If it's just a few days I wrap aluminum foil over the top and put it in the freezer. For this reason I'd rather buy quarts than full gallons, even if it's a little cheaper to buy the galllons.
You can buy a plastic snap-on rim that does a pretty good job of keeping the rim clean.
Galvanized vs. Painting
If I were doing it, I would buy the galvanized, as Jigs-n-fixtures advised. However, maybe you have already bought the beam.
At first glance, paying $600 for galvanized vesus just painting seems like a easy choice to make in favor of painting. But the kind of paint that will do the job as well as galvanized finish is going to be very expensive. And then you have to prep the surface and apply the paint. You also have to apply the paint without making a mistake that would lead to pre-mature paint failure.
You have to also decide exactly which high performance paint to use. There are many conflicting opinions on that point, and many options to choose from. Dealers and manufacturer technical support will run you in circles with conflicting information heavily influenced by their commercial interests.
And finally, paint is generally undergoing radical reformulation to meet regulatory requirements. There are lots of indications that the products are being compromised in this process and not performing as well as they used to.
When I buy I-beams, they offer me galv or not, and primed or not.
I would not think or dream of buying steel not primed. In my climate as in yours, it will start to have a coat of oxides immediately which will interfere with any paint you hope to apply in the future.
Ummm... $600 for a part of a big project... that is durable long term...
DUUUH!
SPEND THE MONEY!
After $120 in paint, $30 in phosphate metal prep, $40 in primer, $20 in sand to sand blast them, and an entire day to prep and paint the beams I don't think you've saved much over the $600 galvanized ones
As long as your beams are out of the weather you don't need to do anything except prime. The "warm, humid SC air" is the same air that surrounds every red iron framed building in the state including buildings that store caustic materials. I've seen an 80 year old steel building that was used to store loose salt at a paper mill that was still in decent shape so don't worry too much about your beams.
Though it is true that if they're in contact with concrete that will result in them constantly being moist. Plus there is electrolytic action between the concrete and steel. It's the concrete/steel junction I'd worry about most.
Every steel building I've ever seen has its post sitting on concrete. One of the local steel fabrication shops here makes custom
culverts for farmers, developers, etc. Depending on diameter that bend flat sheets to the proper curve then weld the pieces together
to make the culvert. Some of these run through salt creeks and none of them are galvanized. I asked about it one day and was told that the culvert would last far longer then the road.
Paint for steel beams
Try KBS rustblast. Or, POR-15. The two are designed for painting the steel sub-frames for cars and trucks being restored. I just finished painting the frame of my 72 Ford Bronco w/ the KBS. You prep the metal (after it's clean) with a KBS self-etching product that leaves a slight zinc coating that heps the rust seal adhere better. The paint is amazing at sealing the steel, even if it's rusty, and creates a moisture barrier. It works for decades on off-road trucks; should have no problem on your deck.
Look it up online KBS rustseal.
Good luck!
metal prep
From someone that has done it, Sherwin williams Chemical coatings group has 3 things that will do great. My I-beams are as new as 15 years ago. A call to them will give you correct current part numbers. However, these all cost and are practical if you can't galvanize and want color, and can be brushed or sprayed. Done right, these coatings are expensive however. There are also other competing versions as well.
1: Pre-Prime, prep
2: Iron-oxide, base
3: Moisture cure urathane, top