The International Cessna^® 170 Association

I'd advise against using a metallic stainless steel brush on aluminum. Despite your best efforts, dissimilar metal will be transferred and electrolysis will become an issue. (It's also condemned by virtually all maintenance authorities.)

John
Many thanks for the tip..............my local LAME suggested the 240 grit paper and I knew there must be an easier way!! I will definately give the Aluma Prep a go as the corrosion is only very light hopefully this will do the trick.

Did you also Alodine and two pot paint after cleaning?

Many thanks

John K

After the final pressure wash, apply alodine according to mfg. instructions and then rinse again thoroughly. After the surface is dry, I apply Dupont strontium chromate two-part epoxy primer. I use the Imron system when painting, you will need to use the primer recommended by the paint manufacturer you are using. Do not mix paint systems. As for the debate re wire brushes, George is correct that the use of a wire brush can leave behind microscopic particles that could promote corrosion, however stainless steel is approved for this purpose. Carbon steel and brass are not. I'd like to cite chapter and verse from the 43.13(b) "bible" but it's at the hanger and I'm not. There is a whole section on corrosion that you should read before you do any more work. Anyway, I always do a final acid wash after any scrubbing to help remove any contaminants that have gotten onto the metal. I get my acid from a local power wash company that calls their product AlumaClean. It runs about US $45-50 for a 5-gal. pail which is way more than you will need for one airplane.

In reading the label just now, the solution I use also contains hydrofluoric acid in addition to the phosphoric acid I mentioned earlier. Even highly diluted, this stuff is not good to get on your skin for prolonged periods. Read up on HF before you use it.

John

PS Regarding the sandpaper, you DO know that aluminum airplanes have little bumps on the skin that are SUPPOSED to be there, right?

John
Many thanks for the tips on the cleaning. I will be discussing our current procedures with my LAME before we progress too far into these wings.

regards JK

gahorn wrote:I'd advise against using a metallic stainless steel brush on aluminum. Despite your best efforts, dissimilar metal will be transferred and electrolysis will become an issue. (It's also condemned by virtually all maintenance authorities.)

The Navy's corrosion control schools disagrees with you on the stainless steel wire brush issue.

My rule of thumb; remove as little material as possible, hence I wouldn't be using a brush in the first place.

c170b53 wrote:My rule of thumb; remove as little material as possible, hence I wouldn't be using a brush in the first place.

So Jim, why wouldn't you use a brush to remove paint softened by paint remover around rivets?

Tom and George were commenting on using brushes so I just made my as usual (maybe flippant) comment. But now that you ask, I guess it depends on what material the brush is made of ? Using a metal brush to mechanically remove material sounds somewhat like an archaeologist using a backhoe to unearth antiquities to me but that's just my opinion. Using a soft brush with paint stripper to mechanically remove paint hasn't worked for me either as the bristles tend to turn into mush much like the paint.
In my experience the hardest areas to remove are around the rivets head perimeters. What I have used to scrape away paint is plexiglass from old windsheilds, broken into hand sized pieces. I'll use stripper to remove all the paint and them 3m pads and water to remove stubborn primer spots. Alumni prep water mix with the pads until fresh water beads away
Yes it takes time to do a good job.

So Jim you think a stainless bristle oversized tooth brush used to remove soft paint around rivets is not a good idea because of lose of material but you will scrub the skin with a Scotchbrite.

I use plastic to remove the soften paint and primer then scotch brite with the alumni prep solution so it's a wet surface and you're just trying to remove just the oxidation. If you had a dry surface with a new pad , yeah you could be removing metal if you leaned into it but I don't think I recommended that technique.

I use a platers brush with stainless steel bristles, and a stick of hard wood as a scraper, a bamboo paint stir works grate after it have been shaped on a sander to a 45 degree bevel. Phenolic works great too. To loosen paint that has been soaked with stripper I shorten the bristles of a throw away natural bristle brushes you get at the Ace Hardware store.

I've used wood and phenolic scrapers with a prepared edge as well, I just find the plexiglass edge remains sharper longer. Having said that, I never thought of bamboo and I bet that works well.

I'm just trying to figure out what size hair it is that is split when discussing the metal removed by hand with a stainless bristle wire brush the size of a large tooth brush and that removed with Scotchbrite and alumni prep while scrubbing to remove oxidation.

I also use plexi with a sharpened edge as a scraper.

I think it comes down to technique, knowledge and experience (what a news flash Jim). Tom is obviously happy with his methods, I'm happy with mine and I'm sure there's variations out there that work just as well. Those new at it will have to balance methods and " production rate" and then evaluate the results, is there any other way?
Bruce you maybe doing a small area, you maybe doing a wing, you may have virgin material, you might be on the aircrafts fourth paint job, each senario will present a different aspect to the surface prep.

T. C. Downey wrote:

gahorn wrote:I'd advise against using a metallic stainless steel brush on aluminum. Despite your best efforts, dissimilar metal will be transferred and electrolysis will become an issue. (It's also condemned by virtually all maintenance authorities.)

The Navy's corrosion control schools disagrees with you on the stainless steel wire brush issue.

The Navy lets pilots jump out of airplanes that other people pay for, and those that aren't jumped out of are thrown away every few years. They also deliberately sink ships when they're finished with them calling them "artificial reefs" because that sounds better than "navigational hazard".

Most General Aviation people prefer to preserve airplanes for long-term use.

Here's the FAA Chapter on Corrosion and Paint removal. Notice they do not recommend any type of metal brushes for paint removal. Notice also Fig. 6-18, which is a dissimilar metals chart. The GREEN areas indicate the dissimilar metas which, if in contact with each other, will corrode heavily because they are so far apart on the activity/passivity chart.
In other words, notice how far apart ALUMINUM and "Corrosion resisting steel" (so-called STAINLESS STEEL) is, because when in contact with each other, they cause corrosion, and is therefore why it's best not to use steel or stainless steel brushes on aluminum. (Hint: Ever hear your A&P warn against using stainless steel screws on your airplane unless you also use nylon insulating washers?)
Here's the AvStop article on the topic: http://avstop.com/maint/corrosion/ch6.html