acid washing your Alloy...

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acid washing your Alloy...

#1

Post by welder »

Just wondering here about home builds and repairs, do you guys acid wash your alloy to remove the mill scale and if not do you see any white patches appearing after the build or repair and if I choose to acid wash what solution should I use. Not trying to start anything just looking for info.
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Re: acid washing your Alloy...

#2

Post by welder »

Oh, if I acid wash my boat what is the best way to neutralize it to stop the etching process?
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Re: acid washing your Alloy...

#3

Post by gandrfab »

welder wrote: Not trying to start anything.
You started this web forum :thumbsup:
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Re: acid washing your Alloy...

#4

Post by goatram »

Kevin answered this awhile ago. You tried to correct me on BD a couple of weeks ago Les.
Aluminum Brightener and lots of water to neutralize the acid.
NAPA or any Truck supply should have it.
http://www.nueratrailerparts.com/p-5015 ... allon.aspx
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Re: acid washing your Alloy...

#5

Post by goatram »

Here is the post by Kevin
"goatram,
when aluminum is 'milled' into sheet that is the 50 series alloy plates and sheet material (generally the industry calls 3/16" or 0.187" thick material the break between plate 1/4" and thinner 0.160" a sheet some folks make that call at 0.125" 1/8") they are surface treated by the rolls with a coating that is shiny in the form of an oxide film

Now all aluminum will form an oxide in a few second by combining with oxygen to form a 0.002 thick layer or film we can't see well, and that is not the 'mill scale' or shiny sheet coating I'm discussing although chemically they are similar. The chrome looking coating on the mill sheet goods is heavier and helps the surface release from the rolling mills and stay clean and smooth.

But - this stuff holds water, is porous, is galvanically different from the underlying parent alloys and will foster corrosion of two types, one type is electrical/galvanic and the other type is to promote poultice corrosion cells.

To etch is to wash this surface film off with acid. Most common products for this use are Zep-a-Lume or Alum-a-Brite both are solutions of phosphoric and hydrofluoric acids; not casual dish washing compounds. Both of these products and many more including the main acids in more concentrated forms are used to spray on and wash off the mill scale film, and any other oxides that have formed.

This process is known as etching.

To paint aluminum effectively, you'd need to etch the oxide films off using an acid then while the acid is still coating the metal flood or heavily rinse the surface with water and keep the water flowing. While the water is flowing then begin to flood the surface with Allodyne (Zinc Chromium Solution) which is a commercial name for a zinc and chromium solution that will bond with the aluminum at a molecular level while the water keeps the oxygen away from the aluminum. This material will form a Chromium Oxide film instead of the weaker and less adhesive Aluminum Oxide film if air were allowed to the metal.

Now, a primer paint or base coat paint can adhere to the aluminum. Primers also can be purchased that are alleged to 'etch' the metal without an acid wash, but the really serious large scale boat and airplane painting operations seem to use the acid then the allodyne then the primer.

Primer's job is not to look good but to be a bonding agent to the Chromium oxide layer and the paint to come as a top or finish film. I'm not discussing the Nyalec coatings in this.

If the finished boat is just etched and left 'raw' it will form an oxide film that will protect the boat from any atmospheric corrosion. That is not a protection against, acidic bilge water or poultice corrosion or galvanic corrosion, or stray current corrosion. All of these types or corrosion can be defended by correct installations on the welded aluminum boat but at the very minimum a finished boat should be etched or mechanically 'buffed' or surface treated to get rid of the 'mill scale' layer so it doesn't bring about premature corrosion sites.

Welding can be done 'too cold' and end up with a surface weld that looks OK, but has inadequate penetration. But, in most cases a weldor who has taken time to 'get his hand in' (phrase to describe a weldor with a consistent bead) has also gained the knowledge of what it takes to make a good weld and the most often want to do good welds AND have them look good too.

I do understand the lure of a higher paying job, with benefits, for the tradesman who is planning to work within the trades for his entire career. I have friends that got out of high school with me, went to union work, not welding mind you, and are already retired and I'm still building skiffs and doing odd jobs while they spend time driving their welded aluminum boats!

Hope this helps to clear up any use of terms not made clear?

Cheers,
Kevin Morin"
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Re: acid washing your Alloy...

#6

Post by kmorin »

welder, goatram, I would add to my (novel length?) post on etching or acid cleaning aluminum that the acids will all dilute to such minute/low/miniscule concentrations they're less active than vinegar down the sink. So neutralizing (using a base to counter the ph until neutral) them is not important. In concentrations out of the bottle they're hazardous (a) waste but once they're diluted (not neutralized) with hundreds of gallons of water they're almost neutral ph. Surely no longer hazardous.

welder, the white flowers are usually an early indication that the metal is forming a poultice corrosion site and this can happen inside or outside the hull. The white flower is often, but not always, the result of a galvanic difference in metals- or with the alloy mill scale that holds water since its porous. The mill scale, if not removed, will form these 'flowers' and if you were to wipe one clean there is most often no (obvious) sign of a pit but there is a few mills of pitting otherwise there is no 'flower making material'.

In other words, the little white bit of chalk or dust is the dry result of the galvanic residue and if you see these indicators it may be time for a little acid rinse to get that mill scale off?

If you look at the main quality builders-they (almost) all deal with this in one way or another- mechanical abrasion works (buffing wheels), chemical abrasion works (acid) but getting mill scale off aluminum is as important as it is in the "magnetic metal".

I know that Jettywolf is going to label me the "millscalenazi" but I have found hundreds of cases of corrosion due to mill scale and none of the same type where is has been properly cleaned off- inside and out. I sound like a broken record- but only to the tune I know so well.

just my dime :deadhorse:

Cheers,
Kevin Morin
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Re: acid washing your Alloy...

#7

Post by JETTYWOLF »

WELDER....

I hope ya got all that :?: :idea:
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Re: acid washing your Alloy...

#8

Post by Katoh »

Kevin
Must ask can you use high pressure washer to remove mill scale from the sheets?
Once you start seeing the problem can you halt it? maybe with cleaning and pressure water or is it all too late?
My questions are also relevant to my rebuild.

I can not see why you gentlemen in the US do not paint your hulls? Here in Aus we tend to paint everything, and I'm sure, but it must help with corrosion. Or maybe just the prep of having it painted helps :?:
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Re: acid washing your Alloy...

#9

Post by kmorin »

Katoh, its really never to late for the marine alloys regarding surface clean up to prevent corrosion. You can acid wash an old boat so it looks 'new'; that is the dull silver gray of the underlying parent metal is always under the oxides on the surface.

If the 'little flowers' or white spots start, you can stop them, usually, by acid washing but just pressure is not going to get the oxides or surface contaminants. Pressure washing will get the marine growth or some of it if you've "grown grass" and it will lift some of the barnacles (not all!) but the layer of mill scale that holds moisture even on a trailer, won't come off with just a pressure washer.

Once the mill scale is removed, then the boat will remain free of the pitting in open, freely drained areas- for a "hundred years" as far as we know?

I think the reason people, here, don't paint as often is the issue of paint maintenance . I think most guys like bare aluminum boats to skip that part of boat ownership? I have both painted and unpainted hulls and the bare boats are less work, even if I may like the looks of the painted boats more. The cost is the second factor, a full paint job sure does add to the cost of an new welded aluminum boat.

The first step in painting is to acid etch (not counting 'self etching primers') so I agree that the paint prep goes along way to helping a new hull get properly prepared for its working life.

Cheers,
Kevin Morin
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Re: acid washing your Alloy...

#10

Post by BeachDweller »

kmorin,

I understand the low maintenance issue with not painting alloy but what about resale? Any impact on one's ability to resale the boat down the road?
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Re: acid washing your Alloy...

#11

Post by jrogers »

I think a bare aluminum boat will look and sell better after 10 years of real use than a painted boat. With painted boats you always have to worry about crevice corrosion anywhere you get a scratch or crack in the paint.
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paint and resale values

#12

Post by kmorin »

Beach,
I've read lots of industry magazine articles, (pro boat builder mag, fab magazines, welding ... ) and over the years I think I've come to accept that the different markets want different looking boats. I think it was a production builder's manager or paint supervisor who made the remark, in one of those articles, that their company paints (side panels only) in order to participate in the market where paint is needed to be accepted.

I guess it makes a difference where the boat will be used, in the old country paint seems more important, I'm here with jrogers & spoiled one, where paint is not common. If there's spare bucks for the boat budget (?) those 'spare $' tend to go into more equipment, horsepower or get burned up in the fuel budget.

A paint job on a 25'er in our area (fully covered, full prep and finish with bottom paint) will run the cost of a new 150hp outboard, and it takes some maintenance; lots of people don't want to spend money for looks they don't 'need'** that only means they have to maintain the 'looks'.

** "Beauty is in the eye of the beholder"

Cheers,
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Re: acid washing your Alloy...

#13

Post by Sculpin »

Lump me in with the Alaskans. I love unpainted aluminum. I like Chaps's blasting of the deck for traction as well then there is zero paint needed except bottom paint if moored.
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Re: acid washing your Alloy...

#14

Post by jrogers »

I don't even have bottom paint and I am in a slip most of the summer. Maybe it is unique to our cold waters, but I just pull the boat a couple of times a year and spray bleach on it. You don't even have to power wash it, just drop it back in the water and all growth is gone.
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Re: acid washing your Alloy...

#15

Post by BeachDweller »

So if I'm reading this correctly acid washing to remove mill scale is a good thing even if the boat is being left unpainted.
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Re: acid washing your Alloy...

#16

Post by kmorin »

Yes, BeachDweller, you are reading this correctly.

Cheers,
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Re: acid washing your Alloy...

#17

Post by johncar »

OK I admit I am a bit confused, My boat a couple of years old for the main part is unpainted and I assume untreated or acid washed at all after it was all welded up and it appears to be Ok with no major corrosion other than areas of small whitish spots, not raised or powdery, they appear to be more like etched silvery spots if anything. A few shiny streaks down the sides where water hits the welds under the deck line and dribbles down.

I didn't want to ever paint it but I would like it to keep a reasonable natural appearance. Should I be concerned or do anything other than just washing down with detergent and fresh water?

In the second pic below there is a discolouration like a tea stain around and just above the water line I think from the previous owner spending many days in estuary systems, It seems very stubborn to any regular cleaners and I would like to clean this off but not game to touch it with anything too severe, any suggestions most welcome. I think it may have faded a little since I have owned it.

Image


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Re: acid washing your Alloy...

#18

Post by johncar »

Must have been a silly question??
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Re: acid washing your Alloy...

#19

Post by kmorin »

johncar, sorry to have missed this post, I don't know if your boat needs to be etched based on your comparison of the exiting corrosion. I use the "rule of thumb" that all mill scale should be removed, and I either do it myself or leave it to the owner, if they prefer to leave it on.... ?

I have seen the interior of hundreds of aluminum boats, those not etched; suffered: those that did etch; did not suffer.

The boat you show seems to have mill scale, so if it were my boat, I'd etch that boat, but since its your boat, you have to inform yourself of the effort, effects, efficiency of the results versus leaving her as she sits. The etch will take off the stain but it may lift some of the paint patches if the edges weren't taped super well.

Windows, molding, trim, carpet, finish work... it all may take a hit from acid etching. I do this process before the boat is finished so I'm not saying your boat will suffer irreparable harm without this process, what I am saying is that the metal will last longer if the mill scale is removed, if that was not done at the time of the build, you have to make the decision if that is worth the effort now?

I'm not sure of the alloy of your hull or its origin 5083? my remarks are about boats I've worked on in Alaska and seen hundreds of examples of production boats from the Puget Sound area coming here with this problem.

Hope this helps, instead of hinders your decision cycle?

Cheers,
Kevin Morin
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Re: acid washing your Alloy...

#20

Post by Sculpin »

Hello Kevin,
Yourself and Pacific Boats are the only ones that I know of that acid wash there boats before launching. Is there more out there? Just asking as I find all this very interesting. You can definately tell if a boat has been acid washed or not. Most aluminum boats I have seen are not. I would just like to rack up a list of builders that do this procedure. My vessel is definately not acid washed as I can still see mill scale and even mill lettering on the inside of the hull. This is all very educational for sure.

Cheers,
John
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Re: acid washing your Alloy...

#21

Post by johncar »

Hello Kevin, Thanks very much for your valued advice. Yes it would definitely seem a difficult job after the boat is all fitted up. It doesn't seem to be a common practice over here although it makes sense if the metal is better off for it.
I guess I will just have to try and stay on top of the maintenance for now.
Not sure what grade of Alloy was used in the hull but I will try and find out.
Regards John
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Re: acid washing your Alloy...

#22

Post by kmorin »

sculpin, I don't have any contact with the name shops, as I'm not in their class just a skiff builder, but I do know the results I've seen in the last four decades working on alloy boats. I have seen several skiffs from different Puget Sound builders, I think one was Workboats Northwest? and it was etched. I've seen plenty of others that were not, and they are group in which I've seen the most corrosion problems of the type we're discussing.

One large and well known builder/manufacturer told their new owner the corrosion in his bilge in less than 6 months was 'normal' and not to be concerned! He was concerned having given nearly a 100k US for the boat. I was asked to look at the boat and found its entire interior was not etched, when he washed the bilge with acid and rinsed the boat, the corrosion was arrested and has not returned. This was a name everyone would recognize- so ignorance on this subject does not seem to be confined to the size of the boat yard or the number of hulls built?

The only method I can think of to explore this is to write/email/call/visit anyone close to you and see what 's being done? It also may help to look at all the aluminum alloy boats you can find to see their surface quality over time?

I have been involved with a few friends whose skiffs were old and they wanted to sell them. Sitting on a trailer with sign didn't draw any interest. I suggested they take time to white metal etch the hulls- and when that was complete both skiffs (years apart) sold in a few days. Appearance is enhanced when the old surface oxide and mill scale are removed.

johncar, acid etching is still questioned (not practiced) here by many builders, so its not like the practice is as common place as it will become as the current crop of boats age and the impact of the mill scale oxide is shown over time.

Image
these young men are fishing in a skiff that was built in 1979 and acid etched and has been fished all summer, then beached and left for the next 8 months and fished again. There has never been a day of "maintenance" of any type related to the surface treatment except to slosh her out of fish blood and gurey (sp?) and the surface is a dull silver without one pit, no flowers, and no corrosion of any kind or type.

Image

This old skiff has been around since the 80's hauling hundreds of tons of fish on to a gravel beach and is the same color and surface as the day she left the shop plus countless bangs and impact into the trailers, tractors, rocks and other immovable objects on the home beach. She was etched when she was built, and the results are that without the slightest maintenance except to wash the bilge and drain and roll her in the winter- she's not shown any corrosion.

My experience with hundreds of skiffs and repair of countless dozens more, and modifications to a third group of hulls shows me a clear pattern of survival of these boats related to the surface of the alloy used to build them.

I'm glad that Jettywolf is off fishing and has a Pacific or I'd be getting the :soap: raz from our resident site 'nazilablermoderator'. But my experience in aluminum boats shows me they're better in the long haul than plastic, cellulose or the rusting metal. Just as that is true that same experience shows me that there are poor means of welding, trailering, and bolting equipment to the boats. And along those same lines within my experience I have found that failing to remove mill scale is an error too.

Cheers,
Kevin Morin
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Re: acid washing your Alloy...

#23

Post by Sculpin »

The more I read into it the more it makes sense. Thanks again for such a great explanation Kevin. I am just trying to figure out how to do some of my inside of hull area's in the near future. I want to make this a project for next winter. You are a great member to have on board this site.

Cheers,
John
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Re: acid washing your Alloy...

#24

Post by BeachDweller »

Kevin,

The build on my new Silver Streak is starting soon so should I be insisting on having the boat acid washed as part of the build? I haven't discussed this yet with the builder so I'm not aware of their policy. I do know they paint most of the boats so one assumes they and other builders use this step but it sounds like we should not assume this to be true at all.


David
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Re: acid washing your Alloy...

#25

Post by kmorin »

beachdweller,
If they paint you may question if they use a self etching primer? (1) or if they use the older and more cumbersome acid etch/rinse/allodyne method before the primer?(2)

Also will the entire bilge be painted,(3) that is will the hull be painted (and therefore prepped) inside and out or just outside and if so only a topsides panel or color band or is the entire hull coated. (4)

once these discussions are opened you should get the 'rest of the story', as old Paul used to say.

If they're only painting areas for graphics and highlights, then you may ask what effort would be added to get the entire boat etched clean to white metal (without streaks regardless of the company name!) if that is not planned.

If the deck will be welded tight, that is an airtight deck I'd definitely discuss the provisions to deal with mill scale- below that surface as you could always etch the boat externally yourself new or at some future point. Etching below decks is important because like the inside of a fuel tank you don't get back in there very often!

I use a 50" wide drum sander to sand off the mill scale on most sheets if I can. This means when the boat is done the mill scale is largely gone, including below deck, and the acid makes a nice white finish that slowly grays to a dull silver color. Below decks mechanical abrasion (sanding, buffing with 3M pads) may the most effective way to clean but I'm not saying that a builder would welcome that added labor or tooling to their already tough job of making money in a competitive market using high cost materials......

In my area, depending on the season I have etched the below deck spaces after they were ready to deck and then let the boat dry out before continuing with the build; its a pain in the build but it works great to accomplish the cleaning.

But, like mechanized TIG welding, I know most builders will tell you I'm full of useless opinions, (well that may not be the terminology used- but you get the drift) and they've "never had any problems". IF so...why not ask if they've remodeled, repaired or any 1959-1962 Shore, Marco or Matsumoto hulls? IF not(?) then I'll stick with my "opinions" and they can stick theirs. I'll consider they're just standing on a lower flying bridge to see 'their' horizon if they won't help you get the boat etched clean of mill scale. I'm not saying it won't cost something but my perspective shows the effort is worth the cost(s).

Lets ask ourselves a rhetorical question? Why do you suppose Pacific considers this important? Its not like they're doing something in their beautifully immaculate building process for superstition- is it? I'd ask (myself) why others don't automatically take these steps???? given someone as high quality as Pacific considers this important?

Cheers,
Kevin Morin
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