Clean and prep cast aluminum for epoxy?

V8 trike

New Member
I’m getting ready to epoxy an assembled transmission. I can blast or pressure wash it. How would y’all prep this before epoxy?
 

Chris_Hamilton

Trying to be the best me, I can be
I'd be leery of traditional abrasive blasting on an assembled (motorcylcle?) transmission. Grit gets everywhere, possibly even inside your tranny. If it's filthy pressure wash it , then hand wash it with lots of Dawn or Dawn Ultra and a red/maroon scotchbrite pad. Only use Dawn or Dawn Ultra or Dawn Platimum. Any other product has unwanted ingredients that could affect the surface.

Then use an aluminum prep wash being sure to rinse it throughly while the product is wet (with itself). Then epoxy immediately. Do not wait longer than 12 hours as aluminum starts to form an oxidation film as soon as the process ends.

 

V8 trike

New Member
Thanks. It’s a car transmission and the rebuilder didn’t get it very clean and I knew I could not blast it. Would vinegar work as a good prep or should I use an aluminum brightener like they use on big truck tanks as long as I don’t let it dry and rinse it real good?
 

Chris_Hamilton

Trying to be the best me, I can be
Thanks. It’s a car transmission and the rebuilder didn’t get it very clean and I knew I could not blast it. Would vinegar work as a good prep or should I use an aluminum brightener like they use on big truck tanks as long as I don’t let it dry and rinse it real good?
Vinegar IMO no. A phosphoric acid based product is what you want to use. Ospho would be a good choice. Cheaper than the dedicated aluminum prep wash's. Most of the marketed aluminum prep wash's are phosphoric acid based as is Ospho.
Wet it with the product, let it work. If it dries re-wet it with more product (scrubbing with a maroon scotchbrite of necessary) and rinse throughly with water while it is still wet. That is very important. If you fail to rinse it off and then epoxy, the epoxy will not adhere.
 

Barry

Paint Fanatic
Staff member
Planes acid treat every day before spraying alodine.
No harm done.
Personally, all I have ever done on new or used transmissions is clean a couple of times with 700, no sanding, and epoxy.
Two of them I see after about 20 years are still outstanding.
 

Jim C

Oldtimer
i use the zep purple industrial cleaner from home depot on aluminum. its a base, not acid so its actually quite a bit more reactive to bare aluminum. not only will the stuff melt away the dirt, oil, grease, etc it will also etch the aluminum surface. spray on and if its heavy grease then scrub with a scrub brush to break it up, hose it off real good, blow it dry and epoxy it. will last years. no blasting, sanding necessary.
 

Chris_Hamilton

Trying to be the best me, I can be
i use the zep purple industrial cleaner from home depot on aluminum. its a base, not acid so its actually quite a bit more reactive to bare aluminum. not only will the stuff melt away the dirt, oil, grease, etc it will also etch the aluminum surface. spray on and if its heavy grease then scrub with a scrub brush to break it up, hose it off real good, blow it dry and epoxy it. will last years. no blasting, sanding necessary.
Ask me what happens when you leave a timing cover for a Honda in a tub of Purple Stuff overnight.:eek:
:D
 

Jim C

Oldtimer
lmao, it turns white and foamy then it pretty much dissolves away. that stuff is sodium hydroxide which is lye, drain or oven cleaner. i use that stuff for everything. its great for cleaning pots and pans and even your shower. haha. probably go through 25-30 gal a year.
 
I’m assuming zep purple, etc is the same as purple power? I used that stuff forever on everything reconditioning wholesale cars. But found when I was cleaning engine bays it was leaving all the aluminum parts white and flakey. Like it was causing corrosion. Obviously it was attacking the aluminum. I rinsed everything very well didn’t seem to matter. So I switched to purple power HD it doesn’t corrode the aluminum.
 

Lostmy65

New Member
For aluminum, I would have thought white vinegar would be strong enough.
But whatever you do use, definitely need to rinse it off and get the epoxy on there within a few hours - that is with aluminum.
 
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