IceShark

Ok I'm back to my bumper pad project and cleaning up the heavy oxidation that was in a few spots under the bumper pads.

Here is what I would like to do. Chemically get rid of the heavy oxidation so I don't abrade the surrounding paint, put a Sherman Williams self etching primer (#988) on the spots, brush on finish coat, wet sand and polish up. Not perfect, but what the hey.

I don't know if this will work or not but that is the plan.

The local Sherman Willams commercial dealer has this Diedrich 970 aluminum cleaner. It contains hydrofluoric acid that will eat lots of stuff including glass! Diedrich isn't sure what it will do to paint since they sell it for aluminum cleaning on buildings with everything covered up and guys in full chemical suits doing the application.

They also say don't use it on anodized aluminum. Was our bumper anodized prior to paint application?

Any comments?

I don't know, maybe I should just pull the bumper off sand it down and respray the whole thing.

Skip Wolfe

Hydroflouric acid is one of the nastiest substances known to man. Spill 100 ml (<3.4 oz)of concentrated acid on your skin and your history. The kicker is that it doesn't burn like sulfuric of hydrochloric - its just absorbed and then it starts reacting with the calcium in your body. I would avoid it if at all possible.

Water944t

We used a stuff called Phospho or something similar when I was in the navy, it can actually revert the oxidation to metal. It was pretty cool to put it on before the primer and watch the rust and oxidation just vanish. Pretty cool chemistry.

A problem you run into on aluminum cars is steel fasteners. Aluminum doesnt corrode, per se, but bimetal corrosion is a bugger. The aluminum just cant handle being in contact with another metal. When you put it all together again, make extra care when you put the steel parts back on.

The Phospho stuff was a little less catastrophic than straight hydrofluoric acid. I used it many times with no (&^$@#) apparent )@#(&$ _( problems from the encounters. Just gloves and a decent respirator (wink, wink). You can paint over it with your primer after about 30 minutes, and it will almost assure a clean application. It held up to the North Atlantic pretty well for long cruises, and that was pretty tough duty that no Porsche should ever see. I dont recall it ever being hostile to other painted surfaces, and it might even have been one of those crazy cool environmentally friendly type things that the Navy was starting to get into.

And after more reflection, how about this?

<a href="http://www.heatbath.com/producta.htm" target="_blank">Removing corrosion from aluminum</a>

Alan C.

HF is mean but it will do the job. If you use the SW product on a anodized surface you may well remove the anodized surface.

As noted it makes a nasty burn on the skin. I have one. Bad news is that you don't know you have been exposed right away.

Alan C.

IceShark

OK, I will stay away from hydrofluoric acid. No sense running those risks or suiting up in chemical gear for this dumb little project. I thought it was sort of strange the way they described the minimum protection requirements (extensive) and to smear on a thick layer of vaseline on any remaining exposed skin. Jeez!

Watter944t, yeah, I know what you are talking about. It is Naval Jelly for aluminum. Active chemical is phosphoric acid which isn't anywhere near as nasty. Guess I will try that out.

I did see that web site you pointed out but I'm not sure where I would get small quantities. I only need to do a total of about 2 square inches. I can get a small quantity of hydrofluoric for free and the Naval Jelly is only 5 bucks at the local marine store.

James86-951

I work for an Aluminum Finishing Company. There are several methods for removal of the oxidation.

1) Alkaline: Sodium Hydroxide or Potassium Hydroxide. It will attack the AL and will not attack the Ferrous components. (Steel) You will have to follow up with Nitric or Sulfuric Acid deoxidizer.

2) Acid: Stay away from HF!! Yes, it will clean the oxidation, but it is a nasty substance that I think (and hope) none of you can get a hold of. In concentrations above 50% the gov't would like to have a chat with you. (Not to mention it will etch the metal as well as cleanit.) Nitric Acid is also nasty, but it will remove the oxidation very well. We sell a variety of chemicals for deoxidation (desmut) of Al; but you have to buy it in 55 gallon drums or 330 gallon totes. You can contact VWR or Fisher Scientific for chemical raw materials.

There are many companies out there that will supply consumer grade chemicals. They won't kill you (quickly) and they will perform.

Again, stay away from HF!!

IceShark

James, oops, I can get 1/2 gallon of this HF for free. I don't know what the concentration is but the instructions say dilute 3 parts water to 1 part HF. And for polished AL 20 parts water to 1 HF. Sounds like it may be at the dangerous level. <img border="0" title="" alt="[Wink]" src="wink.gif" /> Why would the government be interested in it .... is a precursor chemical for some type of explosive like nitric acid is?

Is there any way you could send me an ounce or whatever it takes to do a few square inches of the good stuff you sell? I would really appreciate it.

Thanks, Dan

James86-951

HF is a precursor and main component of several types of chemical weapons. The necrotizing effect has already been discussed. I won't go into the details here.

Even at 10% the HF will do a number on the metal. Often times we will use the inhibited form of HF, (Fluoboric Acid) which is a little less dangerous and agressive.

Most of the stuff we sell will contain chelating agents for long term use. (baths) Send me a PM and I will send you a 100ml or so of the method you choose with technical data sheets for it's use. (I can't send you more since this is just the R&D lab, we don't keep large quantities here.)