Aluminum Anodization Removal

[Guest]

I had read recently in this forum that Easy-Off Oven Cleaner was the ticket to easy anodization removal from aluminum. So I grabbed a can and a few other chemicals and went on an experimental exercise this morning.

I have a client with a very large boat that has a very large windshield that has 5 large panels of glass. Each panel is separated by an aluminum extrusion both top and bottom, and each side. The aluminum over time, since the boat was new in 1978, has become oxidized and blotchy. My job is to refinish the aluminum with a new painted surface in the color of the owner’s choice. This includes first the removal of the anodization from the aluminum, then scuff the surface to 320 grit, prime all the aluminum with self etching primer, and finally to finish topcoat with Awlgrip linear polyurethane paint.

My first job was to figure out how the easiest and quickest method of removing the anodization from the aluminum. I wanted to be able to chemically remove the anodization rather then a physical sanding removal. I had read recently in this forum that Easy-Off Oven Cleaner was the ticket. So I laid up some small test patch areas this morning on a portion of the window frame and used 3 different chemicals for my experiment.

• Easy-Off Oven
• Nu-Calgon Nu-Brite coil cleaner which is Sodium Hydroxide
• Muratic Acid

The results were hands down in favor of Sodium Hydroxide. This stuff is an extremely caustic base chemical. I applied a light coating with a brush and waited for about 3 minutes and it literally turned the anodization to white foam. I then lightly scrubbed off the foam, liquid and residue with a 3M scrubby dipped in water. Presto, I had a clean bare aluminum surface scuffed to my 320 grit.

The Easy-Off and the Muratic Acid test patches did nothing at all to the anodization. So I would highly advise the use of Sodium Hydroxide for any automotive or marine applications where anodization must be removed. You may learn more about the stuff at http://www.nucalgon.com/products/coil_cleaners_nubrite.htm

Below are 2 pics of the windshield assbly.

[simplyconnected]

Good job, Jed. Be careful and do it outside because sodium Hydroxide (LYE) reacts with aluminium and water to release hydrogen gas.

You may consider having the pieces annodized again instead of painting them. The process is not expensive, and comes in different colors (they dye it). I'm wondering why you would remove annodizing, to paint it.

For many centuries, sodium hydroxide was more commonly used for making soap. It is lye. We use it for cleaning drains. You can find it at Home Depot or Lowe's in the plumbing dept.

Thanks for running those tests. I was going to try oven cleaner until you proved it ineffective. That saved me the trouble. By the way, lye works better if you heat the solution and soak your parts. We used to clean industrial (man cooling) fan parts in that. When the concentration and temperature are right, all that grease and dirt melt off. Paint overspray from our paint booth grating comes off, too. Lye works great. - Dave

[Guest]

Good job, Jed. Be careful and do it outside because sodium Hydroxide (LYE) reacts with aluminium and water to release hydrogen gas.

You may consider having the pieces annodized again instead of painting them. The process is not expensive, and comes in different colors (they dye it). I'm wondering why you would remove annodizing, to paint it.

For many centuries, sodium hydroxide was more commonly used for making soap. It is lye. We use it for cleaning drains. You can find it at Home Depot or Lowe's in the plumbing dept. . - Dave

Yes indeed, this is strong stuff. Latex gloves and a respirator are standard equipment. The boat's inside windshield surfaces have plenty of fresh air to the open end of the bridge area.

My feeling is that I must abrade the surface prior to painting. I must remove the oxidation and other contaminates from the metal to get a perfect smooth surface. Roughing the metal surface is required for proper primer adhesion. I am not sure that aluminum self etching primer is effective or would even adhere to an anodized surface. This sodium hydroxide process seems to accomplish all of this prep work in one step.

My grandmother had made bar soap out of bacon grease and lye. She used shavings offf the bar soap in her ringer clothes washer. One of my earliest and fondest childhood memories was the fantastic smell of her fresh laundry. There was nothing better then going to spend the weekend at Grandma's and sleeping in her guest bed with those fresh smelling sheets.