outboard primer - zinc chromate vs epoxy

[powerabout]

The awlgrip story ( which is all epoxy below the top coat)
but you could get away with
alodine ( or whatever chemical is legal) to wash it clean after you have a sanded or blasted it
545 - you can keep coating this as thick as you want just put your pot in the fridge and keep using it
filler if needed ( requires 545 over the filler)
topcoat

You got the standard answer from the guy

[aussiebushman]

Thanks

Alan

You cannot leave the Al unpainted in any underwater application, thats a nonsense!

Blast the surface as mentioned above (soda is my choice), don´t needle, it drives the salts deeper into the surface.
Use (any) etch primer
Apply two layers of (any) thick film epoxy. (if need be, have a microballoons thickened layer of neat EP between them for fairing)
Apply two layers of UV resistant Ep paint or:
just one and antifouling.


Regards
Richard

Anti-fouling on an aluminum lower unit? Please.... not a copper based anti fouling!

Who said copper?

[Frosty]

If its an outboard it would only be submersed when in use!! It can be washed hosed with fresh water after. No?

If its a trailered boat even the hull does'nt need anti fouling it can be sprayed with a bit of WD.

[swade]

This isn't about anti fouling, it's about aluminum corrosion protection. zinc chromate is for aluminum, doesn't have copper...generally what's used though other variants zinc phosphate,etc as epoxy additives are around and used now.

[swade]

heh nevermind me, i did not see the subject had changed to underwater protection doh!

Alan look around sanding blasting my lower unit was pretty cheap (it's not small either off a 130hp), i paid 20 bucks (usd). Unfortunately
they don't normally do it so i didn't take everything down there and of course mid section would have to be removed or done outside.
Lower unit was very pitted from previous owner, sand blasted faired filled with epoxy...looks great. Other parts were just surface corrosion here and there.

Richard are you saying go right over the zinc chromate self etching primer is ok with epoxy primer?

thanks,
shannon

Originally Posted by swade

Richard are you saying go right over the zinc chromate self etching primer is ok with epoxy primer?

Yes!

And Frosty is right. When the boat sits on the trailer most of his life you don´t even need antifouling on the hull.

[swade]

I decided to go with existing zinc chromate primer, going to cover that with epoxy primer, then follow with a single stage urethane. I have another 50hp to repair and paint on my pontoon, so i went ahead and picked up a used supplied air pump and full mask. Given the cost of full mask and replacing organic cartridges when working with these solvents/ iso paints and that it has residual resale value the supplied air seems a better safer investment.

Next time i'd probably sand blast everything,much quicker to drop it off for a few bucks with better results i'd think. Though the areas that I didn't have blasted and abrasive / wire wheeled should be ok. Better would be to remove powerhead from the upper case for a 100% job but removing 10 year old bolts from a salt water engine is challenging i've found to say the least.

[J3]

I think I'll prime with the zinc Chromate, bog with epoxy, then coat with hi-build epoxy primer and finish with polyurethane. If it falls off after a year or two, so be it

25 years ago I started with acid wash, then zinc chromate primer. I was using interlux - the acid had a yellow color and the zinc chromate had a metallic pink hue - I don't think interlux had more than one at that time. Then (don't laugh) for a spectacular failure... I thought I could use some black 2-part VC-tar over the primer. It looked great the month it went on. However the heat from the outdrive made the thick coating "tear" off the bullet and crack on the upper when heat built up. Primer held fine. Had to start over the following year with a thinner top cote of trilux II - that stayed clean looking and defect-free for 5 years before it needed repainting.