BGordon

BGordon

Well Known Member
Howdy everybody,
I potentially could have made a big mistake and would like to get the forum's input. I was pepping my HS skins yesterday and used a PPG DX533 3:1 ratio to clean along the rivet lines in order to prime them. During this some of the cleaner ran through the holes and discolored the outer surfaces, and some even felt as if the cleaner had "eaten away" at the aluminum. I am not worried about the skins being unsightly (paint will eventually cover it) but I am worried about this chemical reaction. Any idea if it will stop, or has it weakend the aluminum enough that it will continue to erode?
I am going to swing by English Color (where I bought it) and ask them at lunch. Just hoping the forum can fill me with warm fuzzies unti then
Thanks,
Brandon
 
Spoke to English Color

Hi again everyone,
I just got back from English Color and the response I got from them was that they had never heard of PPG DX533 etching the aluminum. The lady helping me then did some research on her computer gave me the standard "it shouldn't erode the metal anymore." So I will continue building, but I will watch the skins closely for further degradation.
If this has happened to anyone else out there, I would love your opinion and feedback about what you did.

Brandon
 
If you haven't already done so, I recommend you wash off any alumnaprep off the damaged areas at once.

This material is corrosive, see the MSDS

You state "and some even felt as if the cleaner had "eaten away" at the aluminum."

You are correct, it has eaten the alum.

Maybe stop where you are at, and get a tech consular to take a look at it??

Personally, I would replace any part like you described.
 
Back when I was painting cars, the proper procedure for application was spray on wet, rinse off right away with water. Dry (towel, compressed air) and topcoat (primer) ASAP. If you have any alumaprep that was allowed to dry without rinsing, you may well have issues: paint adhesion, persistent corrosion, etc. I'd call PPG.

ff
 
It is corroded

Brandon,
I concur with Mike. I've been using DX533 for over 10 years. You MUST completely rinse the DX533 off of the part. Corrosion will appear as a darkening of the aluminum. When properly etched, the aluminum will appear dull, but not darker.
The best way to etch your RV parts is by immersing them in the etch for 1 to 3 minutes [depending on dilution level]. I have found that for immersion etching, it's best to dilute the DX533 5 to 1 or 6 to 1. This will require longer soak time in the solution, but makes it less likely that you will "over" etch the parts. Over etching [corrosion] shows up as the non Alclad areas [edges and rivet holes] turning dark gray or black.
If this happens, it's not a big deal, IF you correct it before the rinse water dries off. I correct it by submerging the affected part in a bucket [or other container] of rinse water. Using Nitrile or Latex gloves, rub the affected area with your gloved [never bare] hand until the dark gray comes off. Remove the part and allow to dry or Alodine [depending on IF you are Alodining].
Failure to remove the dark corrosion immediately will require that you mechanically [sand paper or ScotchBrite] remove the darkened, discolored area. If you don't, it's not IF but WHEN the corrosion will come back.
Contact me off list for more detailed info on this.
Charlie Kuss
 
Not necessarily "over-etched"

The dark or black areas is, I believe, the copper in the alloy reacting with the etchant. This will show up on edges of the alclad parts and all over the part on the solid, un-clad, parts. A commerical chromate conversion coating system follows the etching bath with an acid dip to neutralize the etchant (a basic solution). This acid dip will immediately remove the black "smut" and leaves a clean matte finish. The acid is then neutralized with water. The smut does need to be removed before priming or conversion coating (alodine). Phosphoric acid ? Vinegar ?
 
?

minute2 said:
The dark or black areas is, I believe, the copper in the alloy reacting with the etchant. This will show up on edges of the alclad parts and all over the part on the solid, un-clad, parts. A commercial chromate conversion coating system follows the etching bath with an acid dip to neutralize the etchant (a basic solution). This acid dip will immediately remove the black "smut" and leaves a clean matte finish. The acid is then neutralized with water. The smut does need to be removed before priming or conversion coating (alodine). Phosphoric acid ? Vinegar ?
Click to expand...

Kerry,
The discolored film on the non Alclad areas will prevent the Alodine [or primer] from properly adhering if it is not removed in some manner. I am unclear as to what you are trying to state here. Are you saying that the chromate conversion process [aka Alodine, Iridite, etc] will remove this dark film?
It has been my experience that it will not. For Proper chromate conversion, the aluminum surface MUST be completely clean and free of any film or coating.
Perhaps you are referring to an intermediate step which I am unfamiliar with. If so, please expand on this, as I'd like to know more. I fail to see how dipping the contaminated part into phosphoric acid solution would have any positive effect, as the DX533 [and AlumiPrep] ARE phosphoric acid solutions.
I have always simply cleaned off the etching solution [AlumiPrep 33, PPG DX533 and others] by simply submerging the still wet parts in a water rinse tank. This has worked very well for me.
Charlie Kuss
 
minute2 said:
The dark or black areas is, I believe, the copper in the alloy reacting with the etchant. This will show up on edges of the alclad parts and all over the part on the solid, un-clad, parts. snipped
Click to expand...

Any dark area is an oxide layer. It will prevent Alodine or primer from properly adhering to the base metal.
Charlie
 
backwards

I have mixed up my alkalinities. The etchant is acid and the neutralizer is a hydroxide. Water rinses between. Sorry for the confusion. I have not had luck removing the black smut using just water.

Kerry
 
Charlie you are an expert in this field:D Glad to see you back here on VAF.

Do you plan to volunteer with Alodine Dept again at S-n-F 2010? Here is a picture of you from last year explaining how to do things right:D

charlievolunteers.jpg
 
minute2 said:
I have mixed up my alkalinities. The etchant is acid and the neutralizer is a hydroxide. Water rinses between. Sorry for the confusion. I have not had luck removing the black smut using just water.

Kerry
Click to expand...

Kerry,
OK, that makes more sense. As I stated in an earlier post on this thread, if you get the "black smut" as you call it [great name], I submerge the still wet part in rinse water and mechanically remove the smut with a gloved hand. What base solution would you recommend if a builder chose to use that to remove the black smut?
Charlie
PS You only get this black residue [smut] if you leave the part in the etch tank to long [submersion method] or don't apply the rinse water soon enough or apply enough rinse water to the part [sponge or wipe on method].
 
Vladyspassky said:
Charlie you are an expert in this field:D Glad to see you back here on VAF.

Do you plan to volunteer with Alodine Dept again at S-n-F 2010? snipped
Click to expand...

Vlad,
I plan to be there for the Alodining forum from the 16th to the 18th [Friday thru Sunday] Hope to see you there.

Charlie
 
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