painting a C150

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Dan Thomas

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This is good. But after the metal conditioner treatment (containing phosphoric acid) prime with epoxy (PPG DPLF). This term "Etch" the metal or apply "etching primer" is stupid. You are "Cleaning" the metal. You ALWAYS want clean metal and the metal conditioner will do it and then it's ready for the primer coat.
The etching process (phosphoric acid) leaves millions of microscopic pits for the primer to mechanically adhere to. The alodine process converts a very thin layer of the aluminum to an inert material, resistant to corrosion.

Paints of any sort don't stick well to aluminum. It has to be clean, for sure, but it also needs a mechanical bond. Those pits do that.
 

jumpinjan

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...leaves millions of microscopic pits for the primer to mechanically adhere to.
Well it might, but the milling process, done at the aluminum mill, has added many more million craters. The metal prep "cleans" out the dirt in the microscopic world, and it's washed off. That is the IMPORTANT point I want to make. For a better bond consideration, then take an orbital sander with 220/320/400 paper and rough up the surface to open it up then? One should do that anyway after the paint is stripped off. Yes I agree, the alodine process is worth the effort to do, especially on a high-dollar paint job.
Jan
 

Dan Thomas

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Well it might, but the milling process, done at the aluminum mill, has added many more million craters. The metal prep "cleans" out the dirt in the microscopic world, and it's washed off. That is the IMPORTANT point I want to make. For a better bond consideration, then take an orbital sander with 220/320/400 paper and rough up the surface to open it up then? One should do that anyway after the paint is stripped off. Yes I agree, the alodine process is worth the effort to do, especially on a high-dollar paint job.
Jan

The mill rolls a layer of pure aluminum onto the alloy. (Real smooth rollers that leave a mirror finish that doesnt take paint well.) That layer is somewhere around 2% of the sheet thickness, so an .020" sheet (typical skin stuff) will have .0004" of the pure aluminum on each side. That's less than half a thousandth of an inch. Consider that a human hair is about two and a half thou thick (.0025") and we can see that the aluminum is only a sixth the diameter of a hair thick. Really thin. Start using sandpaper on it and you can scuff right through it real fast. I wouldnt use anything harsher than ultrafine Scotchbrite (the gray stuff). And do that wet. And no power equipment. Too fast, too easy for the average dude to rip material off.
 

Scarecrow56

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Thanks for all the replies guys. I really appreciate all the input. I do have a question. I read in one of the posts in here that you use aluminum foil to mask off the airplane. I cannot figure out why this would be. Someone please lemme know why this is or is this just a matter of opinion? Thanks again
 

Dan Thomas

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Thanks for all the replies guys. I really appreciate all the input. I do have a question. I read in one of the posts in here that you use aluminum foil to mask off the airplane. I cannot figure out why this would be. Someone please lemme know why this is or is this just a matter of opinion? Thanks again
You mask off the windows with aluminum foil. The paint stripper won't eat the foil and attack the plastic. Paper will let the stripper through.
 

BBerson

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There is an alternative "wash primer" system. A mix of phosphoric acid and alcohol. Sprays on thin (see through) and left to dry. Sold by Fuller Paint. Not used much. Most use etch and alodine.
 

Scarecrow56

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Thanks Dan, that makes sense now. So, just to be clear, you still use the yellow masking tape typical to auto body? Or are people using frog tape or blue painters tape?
 

BBerson

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Aluminum foil tape is best. We always taped to the window edge. Then ran another tape to cover the gap onto the metal about 1/8" onto the paint. When done stripping the 1/8" strip of paint remaining was scraped off. Can't be too careful. The slightest hole will allow stripper in and damage the window.
Use thick foil.

I owned an aircraft paint shop.
 

Dan Thomas

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Aluminum foil tape is best. We always taped to the window edge. Then ran another tape to cover the gap onto the metal about 1/8" onto the paint. When done stripping the 1/8" strip of paint remaining was scraped off. Can't be too careful. The slightest hole will allow stripper in and damage the window.
Use thick foil.

I owned an aircraft paint shop.
That right there.
 
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