Clear-coating bare aluminum … but with what?

[sbaxter]

My supervisor and I are making outdoor aluminum signs for the three buildings in the university physics department where we work. We're frankly tired of making large signs that get mounted to foam board and look like crap after a couple of years, due to rain and Florida humidity. We modified the design existing sign (which are designed to appear to be bare metal) for one of the buildings and got some sheet aluminum a little thinner than an eighth of an inch thick and had our machine shop cut the contours and lettering on their water jet. There will be a second sheet of aluminum behind the first, which will be spot-painted in gold and candy-apple red to show through the openings in the front sheet. I have been told the whole thing must be clear-coated before it is installed.

The thing is, we're not certain whether the paints we'll use for the coloring will be all of the same type. The clear red will be applied over the bare aluminum itself, and it is my inclination to use Testor's Transparent Red spray paint (we have a few cans of the stuff already) because it is the brightest clear red I have found, but there a couple of other possibilities, including a Duplicolor clear red I found at AutoZone that looks good. The gold paint (really something that looks similar to Tamiya's "Titanium Gold") will probably be a Rustoleum spray over an aluminum primer, and there will be some dark metallic gray applied in a few places as well that will also come from a rattle can. There will also be a water-slide decal on the surface. The rest of the surfaces will retain their bare-metal appearance. They will be mounted to brick walls, mostly high enough to be out of easy reach, and will be attached with stainless steel bolts. If the first finished sample meets approval, we might do a maximum of about eight of these.

In other words, I need a gloss or semi-gloss clear coat that will go over a wide variety of paint without ruining them, and which will also adhere well to the bare metal and hold up reasonably well outdoors. They will be sheltered from direct rain most of the time, but may still get wet if there is a particularly gusty storm or a tropical storm/hurricane. They will also be protected from direct sun for most or all of the day.

Anyone have any recommendations? I looked around online, but the only discussions I saw were for very large projects and didn't have to worry about going over additional paint, or they had to do with people trying to paint aluminum wheels for cars, and the main focus there is durability and resistance to chipping from rocks and other debris.

Personally, I wonder if there might be another way to preserve the appear of the metal that wouldn't require finding a clear coat -- maybe a ceramic car wax or some such thing.

Qapla'

SSB

[irishtrek]

Test, test, test. Do you guys want it to be glossy, semi glossy or flat??

[dizzyfugu]

I'd suggest an overall coat with clear car body varnish, which is, for instance used to seal metallic paints. These are quite resistant to environmental influences and also stable under UV light. Just because the sun does not shine directly onto the item won't mean that it is not exposed to the effects of sunlight - and this includes the paints you might used, too.

[Kylwell]

There's a product called Alumaclear that is made for bonding to raw aluminum. Baring that I'd suggest a 2K urethane clearcoat as they bond incredibly well and do not show wear or yellowing.

[sbaxter]

Test, test, test. Do you guys want it to be glossy, semi glossy or flat??

I want the sign to look like the bare metal as much as possible. If I could, I would try going without the clear coat at all. The aluminum will have random light scratches and sanding marks I will not attempt to remove (it's a feature, not a bug), so I'm thinking a semigloss will be best.

I have done some tests of various clear coats on the type of aluminum sheet we'll use, but not over the colored paints that will be used -- partly because we haven't nailed down some of those yet -- we know the what the colors we want would look like, but not necessarily which actual brands we will buy. There are two or three contenders for each possibility. I also have not figured out a good way to test it under the outdoors over time in the conditions in which it will be displayed.

Some of the clear coats I tried were eliminated already because they just didn't look that great on the bare metal. I also forgot to mention earlier that there will be a laser-printed water-slide decal on the sign as well, depicting our department seal. There's no good way to duplicate that with the water jet.

Qapla'

SSB

[sbaxter]

There's a product called Alumaclear that is made for bonding to raw aluminum. Baring that I'd suggest a 2K urethane clearcoat as they bond incredibly well and do not show wear or yellowing.

I am intrigued more and more by the various 2K clears. I see people using them on model cars and raving not only about the gloss, but also its durability and ease of use overall. Also, it appears from what I have seen that it can be used over almost any other paint without issue, from cheap craft acrylics to things like Alclad chrome paints. On top of that, despite the initial outlay, it is more affordable in the long run than many of the hobby gloss products, or even regular rattle-can clear coats, when you consider how long it will last.

I'm especially interested in this because the roof panel on my actual car needs to be repainted …

I can't find much in the way of reviews on the Alumaclear product, nor additional information about whether, for example, it can be used over decals, painted surfaces, and plastic.

Qapla'

SSB

[sbaxter]

This project is still proceeding. I had cut and sanded some clear acrylic sheet for the painted parts that will be visible through the openings in the metal. After I washed the sanded parts with Dawn and water and then IPA, I primed each with a black sandable primer, and then (after a round of wet-sanding and then washing again as before) four pieces were sprayed with Rust-Oleum's "Universal Advanced Formula Metallic Flat Gunmetal Gray," and the two larger pieces were sprayed with Rust-Oleum's "Gloss Black Automotive Acrylic." The small pieces with the gunmetal turned out great -- nice and smooth. The larger pieces, for whatever reason, looked like crap, with fisheyes and other flaws all over the place; it looked like a bear sneezed on them. The only variable I can think of was the top coat -- all six pieces were cut from the same sheet of acrylic.

I tried wet-sanding the larger parts, but I'm not convinced that it is worth it -- I will likely either strip the paint on those with Citrus Strip and start over, or pivot to using styrene sheet for those two parts. I already have styrene pieces cut to fit. Either way, having had success with the Gunmetal Gray paint, I picked up a can of Gloss Black from the same line and will try that in the next round.

I did bite the bullet and get four rattle cans of "SprayMax" 2K clear -- one matte (for the metallic gunmetal parts), one satin (for the bare aluminum), and two high gloss (for the candy apple red and for my home mailbox, which needs repainting — hence two cans rather than one).

Qapla'

SSB

[southwestforests]

So, basically, still in a "To be continued" stage?

[sbaxter]

So, basically, still in a "To be continued" stage?

Yes — I’ve made some good progress, but still trying to figure out some smaller things as I go. I had a period where I was able to spend a good chunk of my time at work messing with this project — for example, I spent a couple of days down in the machine shop with the shop foreman helping me wet-sand the two main aluminum “bodies” of the signs so each has a similar finish.

Further, there are two horizontal and two vertical quarter-inch lines that cross the sign out near the edges that are in a darker color and also need a different sheen; I didn’t want to try to just mark and mask those at the end of the process. I needed to devise some sort of jig that I could use to scribe the lines, so I would have their boundaries clearly marked through the rest of the process to make it easy to mask them accurately without fretting that they weren’t straight or that the width might change. I eventually decided to get a couple of foot-long pieces of quarter-inch steel key stock — and I also already had two identical 36-inch aluminum rulers in my work space. One piece of the key stock was cut into two 2 1/4-inch pieces, with remainder cut in half, and the other was left as-is. I used the three longer pieces as spacers between the two rulers and I super-glued the two shorter pieces across the ends of the rulers — and, presto — I made a long “slot” scribing guide. I will tape a full size print showing where the the lines need to be on the sign, with a red square marking the point where the lines cross (so I can avoid having the scribed lines cross). I can clamp the guide in place and scribe the lines, then do all the other painting and come back at the end to paint the lines.

If you’re still reading after all that word avalanche, congratulations … I think.

Anyway, I have had to put the project in stasis at work for a bit. A new semester just started, so I have had to photograph all the new graduate students in the department and I am in the middle of editing the results as quickly as I can. At the same time, I am trying to finish the biennial department newsletter, which I and everyone else involved thought WAS 99 percent finished, only to NOW have the department chairman start to pay attention and request a lot of changes and additions. AND, on top of all that, the university closed on Tuesday at noon due to Hurricane Idalia, and will remain closed until this coming Tuesday. I did bring some of the plastic and acrylic parts home with me so I can strip, mask, and possibly repaint them during the break. But today, I have to replace our kitchen faucet.

Qapla’

SSB

[southwestforests]

If you’re still reading after all that word avalanche, congratulations … I think.

Before a health crash in 2005 I could read a paperback sci-fi novel at a rate of a page a minute or more.