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How much removes alclad?

Michael Burbidge

Well Known Member
Does scuffing the surface of alclad aluminum with red scoth-brite pad remove the alclad?

Do scratches in the alclad need to be buffed out?
 
Here's what my "painter-brother" had me doing with all my aluminum and red scotch brite pads; With water running, scrub until the water no longer beads but 'sheens' off the aluminum, rinse, hang-dry then prime :) Rosie
 
its only .002 thick

i think a moderate scrubbing will remove it with the red pad...others argue this TEHO. you can feel the pad increase in resistance when it breaks through and seems to be a different color. the alloy seems very hard compared to the clad. the clad provides no structual strength at all. so if it didnt go deeper than the clad than i would say it does not need to be polished.YMMV
 
Thinner that 0.002

i think a moderate scrubbing will remove it with the red pad...others argue this TEHO. you can feel the pad increase in resistance when it breaks through and seems to be a different color. the alloy seems very hard compared to the clad. the clad provides no structual strength at all. so if it didnt go deeper than the clad than i would say it does not need to be polished.YMMV

William is a bit optimistic with the .002 number....:) ....especially on the thinner skins.

Alcoa states a nominal cladding thickness of 5%

0.016 skin has 0.0008 cladding

0.025 skin has 0.0013 cladding

0.032 skin has 0.0016 cladding

It is very thin, and probably barely perceptible to the fingernail...

A lot of ScotchBrite rubbing will definitely remove it, and as William says, you can see/feel the difference.

I would leave small scratches in until painting... let the painter scuff up the surface just before he paints.

Larger scratches that may be stress riser points should be removed, but again, wait until just before painting, since the removal needed will certainly take off the Alclad which provided corrosion protection... let the paint process protect the "scratch removed" areas.

Alcoa data here...

http://www.alcoa.com/mill_products/catalog/pdf/alloy2024techsheet.pdf

gil A - reading those spec. sheets again...:)
 
This has been debated before, but going over alclad until you've uniformly knocked off the shine will not remove the cladding. It takes a lot of scrubbing to get through it. I'm not saying you can't do it, but it would be pretty hard to do it inadvertantly. Others will disagree, but I've actually tried it with a timer and a micrometer. It takes minutes, not seconds.
 
This has been debated before, but going over alclad until you've uniformly knocked off the shine will not remove the cladding. It takes a lot of scrubbing to get through it. I'm not saying you can't do it, but it would be pretty hard to do it inadvertantly. Others will disagree, but I've actually tried it with a timer and a micrometer. It takes minutes, not seconds.

I agree, to think you're going to cut through the alclad layer quickly is total fantasy. Every single piece I've assembled has been scuffed with the red stuff and I've never come close to going through the alclad.
 
Yes, using a Scotchbrite pad removes the Alclad, ...

But I wonder how much scuffing is required to get through the cladding. I use the red pad before priming, and scuff to a dull gray finish while washing the part, and that doesn't even totally remove the sharpie marks.
 
Does scuffing the surface of alclad aluminum with red scoth-brite pad remove the alclad?

Do scratches in the alclad need to be buffed out?
Alcad is an extremely thin protective of 99% pure aluminum. Certainly scuffing the alclad surface with virtually anything including your fingernail will easily remove the alclad but so what? Follow Van's sensible recommendations as found here and your RV will outlast you.

http://www.vansaircraft.com/pdf/section 5r9a.pdf

Some people tend to overstate the consequences of removing the alclad coating. Many highly polished airplane skins said goodbye to the original alclad years ago. In fact, alodine a common corrosion control chemical, does not react well chemically with pure aluminum. Try dipping alclad aluminum in alodine and see if it assumes the distinctive golden hue....probably not. This link probably gives as good and brief an explanation as any to the virtues and limitations of alclad.

http://www.preairdet.ca/media/Alcad_Tech_Sheet.pdf
 
read

4313 chapters 6 and 4..in that order then make an informed decission. found at http://rgl.faa.gov/Regulatory_and_G...99C827DB9BAAC81B86256B4500596C4E?OpenDocument its free for your viewing pleasure...if your on dial up forget it. its a pdf...

Ricks info was added while i was posting. looks like great info. also looks like the .002 wasnt far off and is close for an average. i see it gets thicker as the sheets get thicker.
 
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A little primer clarification plz..

Okay, so to clarify what you guys are saying is that it takes a lot of scrubbing to totally remove the clad from the aluminum. My question then is ...is it necessary to totally remove the clad prior to priming, or do you only need to scuff the surface in order for the primer to adher to it?
 
ALCLAD explained

In reguards to the ALCLAD, I think most people spend too much time worriying about damaging it..I have spent 30 years in the heavy jet maintenance industry as an airframe specialist with a strong focus on corrosion prevention and ageing aircraft. If you think back, many airlines polished the fuselages to save some paint weight..works OK, but eventually the polishing takes the clad off around rivets ect...worst effect is a little premature greying in those areas..however, on the backside of the skin most are primed/painted. You will also notice (or not notice) any polished Airbus aircraft...Hmmm, because they do not use ALCLAD skins. For our "little airplanes", if you polish, you will polish ,polish,polish..until you paint, but unlikely ever have much corrosion. In reality, a sheet of ALCLAD is much like a sheet of plywood..let it sit in the moisture long and the edges soak up water and things go bad. The best long term protection you can provide is to seal the edges and holes with primer..the holes with steel bolts being most important. Typically our little planes get so much care though, an unprimed aircraft will still outlive the builder !

Scuff it ,sand it,paint it...fly it !
Bill E. RV-4 ..Scuffing and painting now.
 
ive had

good success with lightly scuffing.(grey/green pad for me) just to a satin finish..how do you know its enough...the alumna prep will foam, then alum prep and alodine and prime. as mentioned before unscuffed clad will barely take alodine if at all.
 
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Okay, so to clarify what you guys are saying is that it takes a lot of scrubbing to totally remove the clad from the aluminum. My question then is ...is it necessary to totally remove the clad prior to priming, or do you only need to scuff the surface in order for the primer to adher to it?
The fact is, it takes very little scrubbing to remove the alclad. With a light scrubbing, especially with maroon scotchbrite, the surface will take on a satin look. This is a good thing because you want to rough the surface to promote good adhesion for the primer coat. Even a normally tenacious epoxy primer will flake off a pure alclad surface. As for fuel tanks, you must rough the faying surfaces (say bye bye alclad) so the proseal has something to grab onto.
 
The fact is, it takes very little scrubbing to remove the alclad. With a light scrubbing, especially with maroon scotchbrite, the surface will take on a satin look. This is a good thing because you want to rough the surface to promote good adhesion for the primer coat. Even a normally tenacious epoxy primer will flake off a pure alclad surface. As for fuel tanks, you must rough the faying surfaces (say bye bye alclad) so the proseal has something to grab onto.

I am sorry to disagree here, but it does take more than "very little" scrubbing. I'm not sure what the confusion might be. I suspect that folks are under the impression that once the alclad has been scuffed to a satin appearance that the alclad is gone. This just ain't so. As I said before, get a clock and a mic and go at it. It's not something that will occur by accident.
 
Way too much worry about scratchng through the alclad. It just doesn't take much to scuff it enough. If you're scrubbing the surface you're spending to much time and energy. My motto, don't dwell on it, scuff it, clean it and build on.
 
Stop the insanity

Do your homework on understanding WHY alclad has a pure aluminum surface

Why is anyone removing the pure aluminum surface of Alclad whether by scuffing or any other means? Have people lost their minds? I know of A&P mechanics that apparently eeked their way through A&P school without reading and have continued throughout their life without reading. Had they been curiousness enough to ask "what is Alclad" and then ask why the alloy has a pure aluminum coating they would shine like a diamond amongst a bin full of lumps of coal. Never in my life would I ever imagine people could be so incompetent or ignorant as to remove the pure aluminum coating in order to apply a conversion coating or an aerospace epoxy primer. I've seen people try to alodine alclad and actually COMPLAIN that the surface didn't accept the alodine after the acid etching and soaking in alodine - so they remove the pure aluminum coating by sanding it off. How much does it make to remove the best anti-corrosion coating the metal can have in order to apply an anti-corrosive coating?

Stop sanding the pure aluminum anti-corrosive coating off of Alclad and just use the primer - it sticks to the pure aluminum surface without needing to scuff it up.

Stop the insanity
 
Yes, using a Scotchbrite pad removes the Alclad, and you will need to prime the surface afterward to prevent future corrosion. If you plan on "buffing it out," as you put it, then you are basically referring to polishing the aluminum and having to maintain that polish throughout the life of the surface. Once the Alclad has been even minutely scratched---as with an Anodized or primered surface---the aluminum is vulnerable to the corrosion process. Hope this helps!

I don't believe this to be accurate. I don't know the spec, but I suspect the alcad layer to be about 1 mil or more. Red scuff pads (approx 400 grit) will leave scratches that are well under .1 mil (400 grit has an Ra of .23 microns). I sanded my alclad sheets before priming with 120 grit sandpaper. I tested before hand to see if I would break through the alclad. I had to sand the **** out of the test panel to break through with the 120 grit on a DA sander. I removed about a mil (.001") before breaking through. Not something you could do with a red scuff pad without working at it pretty hard.

For the previous poster, I sanded because the primer sticks MUCH better to an abraded surface. The epoxy primer acts as a corrossion preventer (far superior protection compared to the pure Al), therefore there is no concern in possibly removing the pure Al layer, which is there to provide the same function. If you use alodine, it isn't necessary to abrade, as it chemically creates a surface layer that promotes adhesion. Without abrasion or alodine, you will NOT get good adhesion on glass smooth aluminum. If you don't believe me, find me a paint manufacturer that endorses application of their paint on an aluminum surface without some abrasion or chemical conversion. Excluding self-etch, where it is endorsed, but it doesn't really provide good adhesion.
 
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Stop sanding the pure aluminum anti-corrosive coating off of Alclad and just use the primer - it sticks to the pure aluminum surface without needing to scuff it up.

Sorry, but this is completely incorrect. Please do some research before you provide this type of advice / rant.

How much does it make to remove the best anti-corrosion coating the metal can have in order to apply an anti-corrosive coating?

Also incorrect. Aluminum is not the best corrosion protection. Non-porous surface coatings provide the best protection. Aluminum does corrode. They just layer it on there, because it is more resistant than the aluminum alloy below it.
Larry
 
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I don't believe this to be accurate. I don't know the spec, but I suspect the alcad layer to be about 1 mil or more. Red scuff pads (approx 400 grit) will leave scratches that are well under .1 mil (400 grit has an Ra of .23 microns). I sanded my alclad sheets before priming with 120 grit sandpaper. I tested before hand to see if I would break through the alclad. I had to sand the **** out of the test panel to break through with the 120 grit on a DA sander. I removed about a mil (.001") before breaking through. Not something you could do with a red scuff pad without working at it pretty hard.

....

There is a spec - it was quoted earlier in this thread...

Alcoa states a nominal cladding thickness of 5%

0.016 skin has 0.0008 cladding

0.025 skin has 0.0013 cladding

0.032 skin has 0.0016 cladding
 
Do your homework on understanding WHY alclad has a pure aluminum surface

Why is anyone removing the pure aluminum surface of Alclad whether by scuffing or any other means? Have people lost their minds? I know of A&P mechanics that apparently eeked their way through A&P school without reading and have continued throughout their life without reading. Had they been curiousness enough to ask "what is Alclad" and then ask why the alloy has a pure aluminum coating they would shine like a diamond amongst a bin full of lumps of coal. Never in my life would I ever imagine people could be so incompetent or ignorant as to remove the pure aluminum coating in order to apply a conversion coating or an aerospace epoxy primer. I've seen people try to alodine alclad and actually COMPLAIN that the surface didn't accept the alodine after the acid etching and soaking in alodine - so they remove the pure aluminum coating by sanding it off. How much does it make to remove the best anti-corrosion coating the metal can have in order to apply an anti-corrosive coating?

Stop sanding the pure aluminum anti-corrosive coating off of Alclad and just use the primer - it sticks to the pure aluminum surface without needing to scuff it up.

Stop the insanity

Holy necro-thread Batman! You do realize this debate occurred 10 years ago, right? A whole bunch of RVs have been built in the interim without folks getting too spun up about this.
 
Holy necro-thread Batman! You do realize this debate occurred 10 years ago, right? A whole bunch of RVs have been built in the interim without folks getting too spun up about this.
Not to mention Sonexes, Zeniths, the odd Thorp here and there, and who-knows-how-many others.
 
Not to mention Sonexes, Zeniths, the odd Thorp here and there, and who-knows-how-many others.

You are, of course, aware that Sonex, and Zenith do not use al-clad aluminum. They use 6061 which is much more corrosive resistant than 2024, therefore not needing to be al-clad.
 
When you go through you will know it. The aluminum underneath has a different shade to it than the alclad.

There is a story about a bunch of sprog pilots in the RCAF who were assigned duty to polish the T33s. ONe of them decided that a floor polisher would do the job way quicker. They didn't know what alclad was. You guessed it, they polished it all off. I don't know what the fallout was. Maybe that is why T33s later were all painted? :D
 
The aluminium underneath will still polish. If you remove it all, a good polishing job would look just like polished alclad... But I think it would be hard to uniformly remove it all if you didn't know it was there.
 
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