Finishing Aluminum

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kmorin
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Finishing Aluminum

#1

Post by kmorin »

Lots of owners have boats that may have been painted in the past, some may have boats that were left to weather but have formed different colors and patterns especially on the topsides.

If you're energetic, like Capt'n Dave of the Jettywolf fame, you'll get out the ScotchBrite(tm) buffing pad and some acid and clean the entire hull to a nice mechanical AND chemical finish. But what's involved? Let's take a look at the overall process and some variations that anyone might decide to explore for their own welded aluminum boat.

First, we've all got to agree that there are two ways to finish bare marine alloy aluminum plate. One it to use an acid like Zep-a-Lume (from the Zep Chemical Co.) which is hard to get in some locations where its a controlled substance. Here in rural Alaska, nobody seems to care much so I can buy it easily from retailers but Jettywolf found it to be like asking to buy dynamite in Florida?

Next, you can scratch, sand, buff, rub, and otherwise mechanically work on the surface of aluminum. I constantly mention Scotchbrite(tm) because it calls up a familiar product but there are lots of companies who sell copies of this material for different power abrasive machines. http://www.ahabrasives.com/ here's a link to one of the best suppliers I know about, they're in the West generally but I'm sure they'd ship wherever the customer wanted. They supply a 4" wide belt sander belt AND I've bought larger, 50" drum sander spiral refills from them too. And they have more stuff than in either their catalog or online so call them for great service.

Lets follow the two types of surface treatments a little bit. If your boat has a dock rash, then those are scratches and wont' clean up with simply an acid etch, they'll require some 'sanding' and the term here means one or more types of actually cutting thin layers of the scratched surface way. But, if you hull is smooth and has no scratches, then you may choose to simply chemically clean up the metal.

What is often missed and I'll hope that Capt'n Dave's articles are on your review list to see that I'm not presenting new ideas but simply reviewing the old facts already given; the stronger the acid the more uniform the coloration of a smooth surface will be. A weak acid or a cool or cold metal surface will reduce the acid's de-oxidation power significantly. In fact, I tell people to use a propane torch on the hull and mix their acid with hot water! (and I always whine about using a full BIO-Hazard suit to apply this stuff)

So if you have an older boat and want to make it 'new' you're going to have to get out the sander disk or belt, and sand the entire hull; then etch. The reason for the first method is to take out scratches, deep and shallow, big and small and to leave a series of UNIFORM scratches. NOW...... there are those who can't accept the round sanders' patterns and I'm not finding fault with that or saying they should. But if they won't accept the round sanded/buffed/(3M'd) look those folks will have to get out the belt sander and some rigging to handle the tool and get a long smooth parallel buffer look

Image

The sheer and topsides of this skiff were buffed in a 50" drum sander leaving a long, uniform and fairly finished surface and the deck in the background was buffed by hand with a 7" 3M pad to create a random pattern on wider sheets that would not fit in the drum, AND that would covered by deck paint. The two mechanical methods are shown here for clarity in comparison.

Image
here the hull which is not etched but is buffed, can (I hope?) be compared to the cabin which is both buffed AND white metal etched where the whiteness of the cabin is from the acid being used to remove the oxide, but the hull has not had that process in this photo.

Sand blasting is another alternative to buffing and really cuts so deep and is so uniform that etching is not really needed unless you want the 'white' that comes from etching? When you consider method to recover the bare aluminum look, first is to consider abrasions that need removing and then consider if washing with acid and leaving a uniform white metal finish are the looks your boat needs?

Acid etching to a white metal finish will begin to color in a year, above the waterline, and deepen for several years. If your area's dust has miscellaneous chemicals in it, your boat may color differently than another boat a few states away. IF the water in your area has some minerals in it (?) salt or fresh, then expect some rainbow effects below the waterline if you don't have bottom paint.

I hope this helps anyone considering a refinish of their welded aluminum boat consider some of the implications of different methods and finishes to their boat.

Cheers,
Kevin Morin
Kenai, AK
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Chaps
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Re: Finishing Aluminum

#2

Post by Chaps »

I too have played around with various methods to restore an attractive finish to oxidized hull plating. Probably the fastest and most effective tool I've tried that utilizes coated abrasives on a power machine was with a device called a burnisher that was basically a hand held drum sander. It has a wide variety of sanding and scotchbrite drums available to enable as fine and polished surface as one could desire. It provides a straight line abrasion pattern instead of circular pattern like an orbital sander.

Image

On this boat the bare hull below the lower rub rail was so oxidized and rough that my sandblast masking tape wouldn't properly stick so I had to smooth the surface with a burnisher (like the one pictured above). You can compare the burnished surface above the tape to the oxidized surface above the rub rail. The surface below the tape is is profiled (sandblasted) in prep for application of epoxy primers and bottom paint.
burnished hull.jpg
I've also had good results with sanding plate with an orbital sander to remove oxidation and scratches and then going over that result with glass bead blasting. The glass bead grains are spherical and the process creates a smooth satin finish (instead of a rough sandblast type finish) which gives a pleasing appearance and cause the circular sanding pattern from the orbital sander to disappear. I have not done an entire hull this way but am planning to do a boat this winter utilizing the method.
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goatram
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Re: Finishing Aluminum

#3

Post by goatram »

Bob I have said Machine in hand that you used and posted above. I need to redo my bottom paint next year as well. I need to first add on to my reverse chine to stop the water coming up the bow. AT had a spray rail added on a few years ago to his Pacific to stop the WET BOAT Issues.

Almost ready to bring my girl home for the winter Clean Up, Maintenance, and Mod Cycle to commence.

Kevin does heating the Aluminum Help open the Aluminum up when etching/cleaning? and Why?
John Risser aka goatram
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Re: Finishing Aluminum

#4

Post by Chaps »

goatram wrote:Bob I have said Machine in hand that you used and posted above. I need to redo my bottom paint next year as well. I need to first add on to my reverse chine to stop the water coming up the bow.
Bottom re-coat after only one season? What happened?
1987 24' LaConner pilothouse workboat, 225 Suzuki
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goatram
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Re: Finishing Aluminum

#5

Post by goatram »

Two Seasons Remember.

Got to raise the water line up a little plus there will be some new metal added to the old up in the front area. This boat is wet when running. Bow drops and the water comes right up in the front hits the gunnel and blows back. Nothing to stop it. Last year at LaPush about sunk the boat because it came right up and into my Anchor Locker for three days. I since covered up the Scuppers.
the reverse chine on a duckworth on your sling. Mine is smooth
the reverse chine on a duckworth on your sling. Mine is smooth
the reverse chine on a duckworth on your sling. Mine is smooth
the reverse chine on a duckworth on your sling. Mine is smooth
My Bow on your stand. I am wanting to carry the reverse chine forward to the fron to force water down and away.
My Bow on your stand. I am wanting to carry the reverse chine forward to the fron to force water down and away.
My Bow on your stand. I am wanting to carry the reverse chine forward to the fron to force water down and away.
My Bow on your stand. I am wanting to carry the reverse chine forward to the fron to force water down and away.
John Risser aka goatram
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Re: Finishing Aluminum

#6

Post by Chaps »

Oh yeah, 2 seasons now on that paint. Anyway, so some mods coming and since you've added about a ton of gear she sits a little lower in the water . . . funny how that happens :beer:
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goatram
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Re: Finishing Aluminum

#7

Post by goatram »

yup that me and the boat's story
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kmorin
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Re: Finishing Aluminum

#8

Post by kmorin »

goatram, heating the metal has nothing to do with the metal's surface properties except to pass heat to the acid. Warmer (hot) acid reacts more with the oxides, and does so longer thereby cleaning more. I you warm the acid with hot water/warm water mix dilution, and then heat the metal the reaction is stronger for any given volume of acid.

I spray the acid on if possible, so that cools the liquid in the process but if sprayed onto warmed metal the acids' cleaning is greater. Using less acid, saving some dollars and getting as clean as one coat will etch. Sometimes in patches that have lots of grime ground into the surface of the metal, like a buoy pressing against the dock for months leaving a large dark stain of grey and black, these areas will not fully clean as the acid cools and stops reacting (partially neutralizing or reducing ph) before the entire stain is gone. So heating is one method to use to help get a white metal etch.

Adding a reverse chine to the flush chine on your boat looks like a good way to help knock down spray, an unequal leg angle (6061-T6) cut to a V aft to fair into the existing angle, and then tapered slightly (not fully) in the run forward would allow the new chine to fit to the old, changing the original taper into a longer, more gradual taper. When the after overlapping V (4-6'long) was final welded, I'd sand the entire aft surfaces and its likely you'll not notice the chine is an adder?

I like to run spray rails all the way forward, to the bow stem or the sheer, if I the skipper allows me? Not everyone likes the looks of the side rails run as far forward, preferring to have them stop at the Master Station and this is especially true if the side rail(s) are hull stiffener extrusion as it appears your boat has?

I like the unequal legged angles, where the upper leg is taller by some than the lower more horizontal leg, forming a good spray deflection away from the boat, and I use this to stiffen the hull's topsides panel as well. Typically I'll run a 1/2" radius, carbide, round-over bit on outer edge of these angles so the factory extrusion is softened that small amount.

Image

This side rail is 4" x 2" x 1/4" and tapered for about 8' at the bow, it does take some tooling to put these on but by following the sheer the look seems to make them less obtrusive to most owners than straight line runs? But then, I've had owners who wouldn't accept the rail line all the way to the stem, even knowing it sure does help dry out the boat. (This boat has a reverse chine plate from stem to stern, so its not as much and issue down low as it spray would be higher on the hull.)

Cheers,
Kevin Morin
Kenai, AK
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Re: Finishing Aluminum

#9

Post by Chaps »

Kevin that's a burly looking boat, is it a recent build? How will it be powered?
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Re: Finishing Aluminum

#10

Post by Derekm »

Kevin documented the build in this thread

http://aluminumalloyboats.com/viewtopic.php?f=49&t=4143
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