rv

I would like to know what should be done to painted aluminum that has some corrosion. What is the best way to get rid of the corrosion in the pitted area on aluminum so the paint will stick and not fail after being in the water.

Thanks,
Rick

James

Rick,

There are no tricks, just hard work - First you must remove embedded salts, look for salt away or Chlorrid at the local boat store - use this on corroded areas - scrub or use a wire brush or power washer to remove corrosion. Repeat this process several time or spend the extra $ 20.00 and get the Chloride test kit. Once the salts are gone, blast clean affected areas using a medium grit 70- 100 size @ 120 psi - then rewash with salt remover. Best paint job in the world will not help if you have a wet chlorride ion imbedded. Pretreat with alodine 5700, prime polyamide epoxy and top coat based on service condition. If you need to fill corrosion pits do that after the first coat of epoxy. Brand of paint is not important as long as you use the same brand from start to finish.

* If you can not find alodine 5700 you may use "Vinyl Wash Primer ". Apply vinyl wash VERY thin just enough to change the color.

rv

James,
Thanks for all the detailed info. I have a followup question. I am a novice at this but I thought I heard someone say that filler (for pits that need it) should be applied to bare metal. You indicated to use filler after applying the epoxy primer. Will the filler hold as well over primer comparied to bare metal. Also, what type of filler to use. Again I was told to use MarineTex (hard to sand but will stay put). Regular body filler will not stick in marine environment? Is this true?

Thanks again,
Rick

James

Rick,
It is never simple - If you put the filler on after priming with epoxy you will limit the exposure time of the raw cleaned aluminum to the elements. The fillers are not smart enough to know if they are being applied to epoxy paint or bare metal. If you use MarineTex as an example you can apply direct to metal, I would still rather see this applied over primer. If you use a polyester based filler (like used for autobodies) these materials will often absorb moisture, if you happen to have a stray chloride cell and it is dry then you just compromised your hard work. Apply polyester fillers over primer and then prime again with epoxy to sandwhich the material.

A great looking job is not worth a sh$^& if you have the base metal contaminated.

As a rule of thumb - do not let epoxy primer stand for more than 7 days @ 77 degrees before you top coat or it will become too hard for good adhesion. ( keep in mind there are 1,000 tyeps and brands of epoxy - read the directions)

* Marine tex is a pain in the ass to feather the edge once it get hard -

IHTFP

James,

Where do I find a chloride test kit?

Thanks

James

Chloride test kits -

www.chlor-rid.com look up test kits -

The kit has a condom in it - break the vial of solution into the condom - place the condom on a verticle or horizontal surface - rub the outside of the condom so the liquid inside the condome touches the surface to be tested - look for the color of the test solution and this will tell you chloride % in ppm's - It sounds like a pain in the ass - but it is worth the trouble and you will learn a lot on "invisable contamination" -

I think a kit is $ 15 - 20.00 each - get 2 or 3

To remove the salts -" Chlor-rid Company" has solutions and a company "salt away" . Be careful of the "clean water" you use to clean the surface. Tap water is ususally clean enough - Well water may have high ppm's. If you are doing small areas couple of gallons of De-mineralized water form the grocery store will set you back $ 2.00 - 3.00

Gmoney52

Have you used Evercoats' "Metal-2-Metal" catalized alumium filler? It is water-proof and bonds good with properly prepared alumium. You have taught me something; I only used PPGs' alumium metal prep before Variprime(or Zinc Chromate) then K36. Have I been fumbling on the 99 yard line?G$

James

Any material used per data sheet is a good material to use - I'm not familar with that product however. Stick to a single product line - many time primers designed for aluminum for instance are Ph adjusted to be aggresively acidic - when you stack other coatings that may also be acidic - if the coatings are exposed to and retain atmospheric moisture before or while being painted this can re-initiate the acididity and actually cause corrosion - Keep the same mfger product from start to finish do not apply too much of each ( paint thickness is measured in mils, not number of coats) and the project will work well -

* Coatings like zinc chromate may be an "alkyd" based material and in fact do more harm than good - Alkyds top coated with epoxy will have an intercoat delamination because the alkyds may not be tolerant to the solvents in the epoxy -

IHTFP

James,

Thanks for the help. I am refinishing an Arneson Drive and want to get the best finish possible.

James

You will find that older arneson casting can corrode quickly and with deep pits - for sure use a "salt removing solution" wash - blast clean and wash again - I suggest that you will have agressive pitting - I suggest that the cleaned casting is primed first ( epoxy) then apply fillers for this application. The idea is that if the fillers ever move or hydrate then the substraight is still protected - I know you said that the filler can be applied direct to metal - but with Immersion use don' t take any chances -