Runoff From Acid Wash Rinse Water

[ehsvp]

I'm interested in preparing the interior of my alloy boat for painting by using the acid wash, Allodyne, primer, paint method. I've read the methods used by Kevin and others on the forum. My question is about the rinse water runoff used for the acid wash-Allodyne portion of the preparation. This is a home build and I'd like to paint it at my house as well. Can the acid wash-allodyne water come in contact with concrete? Will it harm plants,trees or grass? I'd be curious to find out how the commercial alloy builders deal with this issue. Thanks in advance,

Bob

[kmorin]

ehsvp , several questions here and the regulatory agencies figure in my reply.

First acid's negative environmental impact is solely a matter of concentration of molecules. If you have lots and lots of acid molecules concentrated together they can dissolve glass, a foot of steel and a lot of other seemingly solid items. BUttttt (and that is one big round one) for the sake of discussion, if you add some water to dilute NOT NEUTRALIZE.... the effect and affect of acids is seriously reduced.

Let's take some serious high acidic (ph number) Zep-a-lume which contains a mixture of Hydrofluoric, Hydrochloric and Sulfuric acids (!) and put it on the aluminum hot (cranks the reactivity of the acid), and full concentrate (also more reactive) and do that on a hot day, with a sun-warmed boat? Now that stuff should remove the scale, the oxide and any other surface contaminants- and do it quickly!

Buttt... if you put one teaspoon of that same acid in a cold gallon of water, on a cold day, on a boat sitting outside... what happens? The acid won't do much to clean the surface. Reactivity is proportional to temperature, concentration and the substrate (boat temp.).

So, concentration or dilution is what you're asking about but may not be using those terms? If you take a film of pure ONE MOLAR acid concentrate- say a couple of micron's thick (? sprayed on) and wait 'til it reacts and rinse it off? The volume of rinse water to acid is from 100 to 1000 to one: all depending on the rinse volume which governs the resulting dilution of the previously strong ph (acid solution).

What happens in the rinse is that the water used to flush the acid so dilutes the original ph that you end up with a solution less than vinegar in ph!

Yes, the acid rinsed off the boat can come in contact with your lawn and not really have an impact- dilution renders the acid to less pollution than a typical parking lot runoff in toxicity!

Now to the problem for builders. Hopefully some full-time, large scale builder will respond? Absent that; I'll paint the regulatory picture so you're tuned. Anything, any compound, any scent, any doggone compound that COULD in anyone's system potentiality cause some problem..... to ANY person--- is regulated. So acid etching aluminum, which if sprayed on 2nd grade children; raw.... might harm them (not that any builder of welded metal boats would do that.. ) is regulated in some manner or another. Therefore: commercial builders who may- and there are too few who do so [I've sniveled about this for years] would be regulated in their handling, use, and disposal of etching acids.

But what is the chemical reality of acid? If you add enough water all acid becomes "water".

Now let's address allodyne. This is 10000000000% not the same issue because of the chemical reality of this compound. Allodyne is a solution of chromium and even diluted is a big deal. So I'm trying to ask you to consider the two compounds as desperate and NOT in any way equal- please do not consider the two chemical groups as "the same".

Turning chromium salts loose in rinse water is not remotely related to diluting even a strong acid- don't do it.

When you use Allodyne the main chromium component would combine with the bare (etched and stripped of oxide) aluminum and form the layer that primer will adhere too, and that reaction bonds the chromium to the aluminum. This is done when the acid has removed the aluminum oxide and the rinse water has shielded the underlying aluminum from oxygen so the chromium, which works "underwater" is the primary reactive 'salt'.

Therefore, there is little chromium to rinse off. If the allodyne is not reacted to the etched (oxide stripped) aluminum, that material is way too toxic to release to the environment.

Hope I'm makin' sense? Please let me know if we need to go over this in more detail?

cheer,
Kevin Morin
Kenai, AK

[ehsvp]

Thanks for the reply Kevin. So, if I understand your response correctly, the acid used for etching will be diluted so extensively with the rinse water that it will not be a problem. And with the Allodyne, if you are using it correctly, very little of the chromium will be released into the rinse water. If you don't mind me asking, do you perform this process at your boat building shop? Have you had any other problems with it?

Finally one other question, instead of using the Allodyne, could an etching primer be substituted?

Bob

[kmorin]

Bob, that is correct, the acid dilution usually renders it almost neutral ph, but the MSDS for allodyne and similar chromium solutions shows that is not a very good item to release.

I've etched and allodyne coated in many circumstances, outdoors on pavement with municipal drains, on gravel where I'm pretty sure the chromium is still in the ground, and in shops where there were just floor drains. I'm not building full time and the last few boats I built were etched by others, but not painted that I'm aware.

I usually get into all the PPE I own except flotation and fall restraint; after heating the acid in warm dilution water (50:50 depending on outdoor temp) and many times I have someone heat the boat hull with a propane torch ahead of spraying the acid on. I typically work bottom up, spray on (have used weed sprayers and paint sprayers both) and a swath about an arm's reach wide, then allow the mix to foam up (etching action) and then rinse. So a couple people helping is my typical method. Heating, apply acid, rinsing, but that is all based on temp. If the acid and metal are cold the etching action can take repeated applications to get a nice white metal etch... that's expensive so heating is a variable based on the spot tests with the acid.

If the boat has decks where you will have an overboard or freeing port (?) that area can become very white, as the deck and cabin rinse water flows over one place for a longer time than the rest of the boat.... in that case I usually try get it etched first, from chine to deck, and then the 'extra white' flow lines aren't as contrasting to the rest of the hull.

I've used Zep-a-Lume directly out of the bottle, and seen others dilute it two or three to one, and again, temp seems the biggest factor next to concentration. Spraying acid means you could inhale it, and that is not acceptable- it could in fact be lethal due to complications of pneumonia. I wear knee high boots, rain suit (oil skins full suit) a painters' hood, a half face APR w/ charcoal cartridges and dust filters too, safety splash type goggles, face shield, disposable gloves under elbow length 'parts washer gloves'.

My main problems have been getting allodyne onto the wet aluminum before the air got to the metal. That area will show a color change (bluish) in the allodyne film. This implies that you've got to re-etch that area, and re-rinse and allodyne while its wet to get the green to gold colors indicating the chromium oxide film. Trying to go too far and too fast seems to be the slowest method here- at least for me- I ended up with more rework than working at a slower and methodical pace of rinsing and adding allodyne to the wet aluminum.

I've not used self etching primer because of the mixed results I've seen here in our area. One builder has had very good luck, but another several have had some paint lift too. So, not being experienced with self etching primer, I'm just don't have the knowledge to reply on that. If the self-etching primer were not effective I think it would be widely known? and I don't know the level of skill or knowledge in painting of those who's boats' paint jobs failed.

Maybe Chaps, who is the resident expert on coating aluminum, will drop by an give a report on his methods, handling, chemicals and results? Tap, Tap, Tap, Chaps, is this thing on? Bob, if he doesn't see the thread don't hesitate to PM his user name to get his take, he's done more in this area of work than all of us combined; times a large number. And in Chaps' case- he's done this work "ala-Michaelangelo" - overhead!

hope all this helps in some way as part of your planning or the actual work of etching you boat?

cheers,
Kevin Morin
Kenai, AK

[Chaps]

When it comes to successfully painting aluminum used in marine applications I advocate profiling the metal by sandblasting and applying an epoxy primer then followup with whatever top coat is desired. It works well, is relatively fast, doesn't involve any nasty acids or other chemicals and long term adhesion is excellent. That said I'm only doing hull bottoms so my blasting mess ends up on the floor where it is easy to sweep up. To sandblast topsides and cabin interiors as a prep process would pump so much grit into the boat that the clean-up would take longer than the blasting and painting processes combined so for the op's intended project it wouldn't be ideal. I'll suggest you consider a primer system like Pettit 6455/044 but go over all the surfaces first with a scotch pad and strong detergent to make sure the metal is spotlessly clean as the etch won't work on spots contaminated with dirt, grease, etc. Simply sanding is also an option that should be considered. Anything you can do to provide your primer with a roughened surface to grab onto is a plus.

[ehsvp]

Dear Chaps,
Thanks for your painting advice. You discussed several problems that I was going to ask about which were bothering me regarding the paint job. I'm going to use Zolatone 20 on the inside of the cabin, the bridge and the inside of the back deck walls. The rest of the exterior of the boat is going to be painted with Alexseal paint. Alexseal specifically recommends sand blasting before paint and as you mentioned, I couldn't see trying to remove all the grit from inside, especially inside the cuddy. Unfortunately, I did not remove the mill scale from the bilge area before building and would like to before the final install of the gas tank, pumps etc. Do you think I should use the etching acid in this area and wash it out of the bilge with rinse water? The boat is going to be used in fresh water only. How do you protect any aluminum surface inside the cabin which is going to be covered with foam for insulation? Thanks,


Bob