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Best way is to acid etch them with any aluminum etch from the auto parts store. You mix the stuff with water in a pail and dip the letters in. Wear safety gloves and do not breath the fumes. Mostly hydrogen...better do it outside.
Then use Sherwin Williams Zinc Chromate (oil based) primer. It is a dirty yellow color, compared to tohers out there that are bright green. Scuff and then you are good to go with a finish enamel.
I painted an aluminum panel this way 24 years ago for a sign that was outside untioll last year, when I rescued it and brought it home. The paint still is sticking. I did use hardener in the Lettering enamel from Martin Senour.
Lotta work for a permanent solution, but it pays to see your work hold up decades later.
-------------------- Preston McCall 112 Rim Road Santa Fe, New Mexico 87501 text: 5056607370 Posts: 1558 | From: Santa Fe, New Mexico | Registered: Nov 1998
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We use the same method Si suggested. Simple and effective. We give the surface a sanding with a random orbit sander as the last step in fabrication before degreasing. We've quit routing aluminum on our router (except for Dibond). What with the coolant fluid and the fact you can't use your dust pickup system when routering aluminum, it creats such a bloody mess. We buy finished letters from Gemini. We've crunched the numbers, and it just isn't worth it for us to do them in-house.
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raw aluminum, acid etch, zinc primer PPG, and the 2 part epoxy on that THEN topcoat....its a pain and I hate doin it and I gotta agree with duncan buy them outright if you can
-------------------- You ever notice how easily accessible people are when they are requiring your services but once they get invoice you can't reach them anymore
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if it's something gemini can't handle, save yourself a ton of work, materials and fumes and find a good powder coater, we use dynamic fx in Goderich, cheap, good and i don't have to do it! He used to own a signshop, then smartened up!!!!!
-------------------- Pete Payne Willowlake Design/Canadian Signcrafters Bayfield, ON
I take one extra step. I do a degreasing wash both before AND after sanding the bare aluminum. Sometime surface contaminants can be ground into the aluminum by the sanding itself, so I wash the surface with lacquer thinner first, then DA sand with 150 grit, then wash again.
Our primer is an acid wash, self-etching one made by Matthews called PT Filler. You add the activator just before spraying. The activator contains phosphoric acid. Spray it nice and wet to give the acid time to bite. Then topcoat with polyurethane.
Most automotive paint makers offer a self-etching primer that is similar. A two-stage epoxy would be my second choice. Some of the self-etching primers are not recommended over previously painted aluminum, in which case an epoxy primer would be my first choice.
Brad in Kansas City
-------------------- Brad Ferguson See More Signs 7931 Wornall Rd Kansas City, MO 64111 signbrad@yahoo.com 816-739-7316 Posts: 1230 | From: Kansas City, MO, USA | Registered: Nov 1998
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