Aluma bright

General boating discussion
Kevind
Posts: 4
Joined: Mon Apr 04, 2016 8:29 pm
7

Aluma bright

#1

Post by Kevind »

Hi all new member here and have a couple of question. First a little back ground. I own a 22' searunner and I have removed the foam from the floor and sanded it using 120 grit where I could and a vinyl wheel to get to other areas I couldn't with a palm sander and the weld joints. The hull looked good not much corrosion but the box beam and the deck supports have some pitting where the wood was touching the aluminum and around the screw holes when there was water. i think I will sand down the tops of the box beams with some 80 grit paper to get to more of the smaller pitted areas. I will use some aluma bright after to acid etch but have a couple of questions. I have the fuel tank (plastic) will the acid damage the tank? Also do I have to worry about any electrical wires be affected by the aluma bright if it gets on them? Will it effect the bilge pump? Final question for now the box beam has foam in it that I can't remove unless I cut it open and get it welded which I don't want to do but the acid will be in contact with it as the box beam isn't fully welded along the bottom. Should I put some marine calk along the joint to stop the acid from getting into the bottom of the box beam or will flushing it with water be enough to get rid of the aluma bright?

Thanks all
Kevind
Posts: 4
Joined: Mon Apr 04, 2016 8:29 pm
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Re: Aluma bright

#2

Post by Kevind »

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Chaps
Donator '09
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Re: Aluma bright

#3

Post by Chaps »

I wouldn't be sloshing a bunch of acid around below decks. You've done good work cleaning things up manually. Apply acid on your pitted areas sparingly with a small paintbrush and as you get areas cleaned up and etched out sprinkle dry baking soda on those spots to neutralize. When you get all the areas etched and neutralized then flush out entire bilge with the water hose. Are you going to treat or coat the corroded areas?
1987 24' LaConner pilothouse workboat, 225 Suzuki
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Kevind
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Joined: Mon Apr 04, 2016 8:29 pm
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Re: Aluma bright

#4

Post by Kevind »

Hi Chaps,

Thanks for the reply. I was going to just acid wash it and when i put the deck back use some type of spacer so the wood doesnt touch the aluminum. I'll probably seal the wood with a epoxy sealer. i was guessing that the sanding and wheel grinding plus the acid would kill any corrosion. What type of treatment are you thinking? i dont want to paint it as its hard to see if its getting worse as a lot of the corrosion was hidden under the original paint.
Chaps
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Re: Aluma bright

#5

Post by Chaps »

I'd suggest painting all of the pitted areas (and other areas needing protection) with Pettit Alumaprotect epoxy. Its an anti-corrosion formula that is thin so it soaks into rough areas well and it gets hard and is tough. The corrosion fighter in it is strontium chromate.
1987 24' LaConner pilothouse workboat, 225 Suzuki
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Kevind
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Joined: Mon Apr 04, 2016 8:29 pm
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Re: Aluma bright

#6

Post by Kevind »

I got back to working on the boat last weekend and finished up the sanding, nylon wheel brushing and sand blasting with glass grit. I will take a few pics to post. before i start the acid etching with aluma bright should i wipe down the aluminum with acetone or some other product?

I'm also thinking i might do the back deck in aluminum instead of putting back the plywood. I'm not putting back foam so what you put some type of rubber gasket between the aluminum deck and the aluminum structure for noise? the deck will be screwed down like the plywood was with stainless screws and i will be using the anti corrosion gel that i have. I will also be using 1/8" thick aluminum plate as it seems like what most people go with.
kmorin
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Re: Aluma bright

#7

Post by kmorin »

kevind, the reason to use a solvent like acetone is to remove greases, oils, non-water solubles that won't usually come off with acid etching as easily. So if you've been working dry, cleaning and abrading with fiber brushes wire brushes or nylon wheels, then there's no reason to use acetone, but if you have paint residue, or any hydrocarbons- then it can't hurt.

Plate deck over flat rib tops that are not welded sealed shut of water, even rain, will become a probelem again. The issue is creating an unsealed space that is flat plate to flat bar or box rib frame. The flat allows a thin film of water to stay, that de-aerates and that results in acid which usually promotes the crevice cell- all due to the lack of excluding moisture from the joint.

Like Chaps mentioned, if the rib tops, deck beams and any other flat deck-supporting surfaces were to be painted- that is etched, primer chromate painted - maybe through in some high build coal tar or some other well anchored to the rib tops paint- then the moisture can't get to the lower surface of metal to corrode? Also the screws being SS will build in a galvanic potential- If possible to find?? (don't know that they are) a hot dipped galvanized screw would have less galvanic potential (zinc to Alum. vs SS to Alum.) so the corrosion of the hot dipped zinc is less than SS .

Using thread goops does help to reduce by insulating but it too often not a real long term solution to aluminum and non-aluminum fastener joints. Using 5200 (requires heating the fasteners to get them out) works as well as other goops. Since it won't be sealed and may need to be removed again, I'd suggest you consider large size, aluminum wall/barrel/body, rivets with some goop in a slightly over sized hole for the rivet body. The idea is to reduce galvanic corrosion, you're not sealing the deck anyway, and to make the rivets removable by drilling out- AS long AS you can recover any parts of the rivet that will be dropped into the bilge!!!! (!!!!!!) otherwise that won't work- and will likely be harm to your boat.

if you fit the deck panels, and put some bedding/calking/sealant ontop of the painted deck support areas, then riveted down the deck while the calk was wet enough to flatten- that would reduce water from the interface- that's good. The rivet, bedded in sealant or tefgel, will be the least active site IF you can get the blind side rivets' compression element to grasp under your deck beams or supports and the rivets don't leave anything in your bilge that can react with the hull. There are some very large size, blind install rivets used in the inside of highway trailers for both aluminum and ply wood paneling, not sure of the cost or tooling required but its worth a look to see if you can skip screws?

Just another few cents to consider in the discussion.

Cheers,
Kevin Morin
Kenai, AK
kmorin
John@Ironwood
Posts: 21
Joined: Wed Aug 01, 2012 11:19 am
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Re: Aluma bright

#8

Post by John@Ironwood »

FYI...Hydrogen is a byproduct of aluminum cleaner/brighter.
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