Topic: How long is too long for Phosphoric acid?

[leaderbean]

So I am stripping a spare 550 tank of its old kreem coat / underlying rust. 

I used MEK followed by "Must For Rust".  Both have worked great but tonight I neutralized the acid and dumped it out, only to see the interior of the tank rust up almost immediately.  I wasn't really watching, but I bet you could have actually watched it rust in real time.  I was bummed. 

I was going to get some acetone in there followed with a shake of diesel to prevent this rust, but I didn't even have time.

So now I have to start the de-rusting all over again tomorrow.

Also, I want to por15 it but I don't have the kit yet.  Should I let the acid sit in there till I get the por15, occasionally shaking it around to prevent rusting?  Or should I continue with the Acetone followed by Diesel?  Then go back to the acid again when I get the por15 kit? 

I don't want the whole kit seeing as I already have the same acid prep.  I might do some calling around the Twin Cities here tomorrow trying to find a Por15 seller/distributor or something.

[TwoTired]

Phosphoric acid is supposed to convert the inner surface with a phosphate coating.  It is sort of self limiting as the coating block further contact with the acid.  No way it should flash rust afterward.

You sure you have phosphoric acid?  Or, is it another acid type?

[BeSeeingYou]

What did you use to neutralize the acid?  A couple of tablespoons of baking soda in a quart of water has always worked for me.  I have not used phosphoric acid but others here have and it is supposed to leave a zinc phosphate coating that prevents flash rust.  I have had very good luck using CLR to remove surface/flash rust followed by the baking soda rinse and then an alcohol rinse to remove the water followed by transmission fluid to coat and protect the tank till use.  I know you had to use the MEK/acetone to get the liner out but I would stop using that stuff now, it's just too nasty.  Don't let the acid sit in there long and when you neutralize it swish it all around the tank top and bottom even if the acid only sat in the bottom of the tank.  The fumes alone will leave an acid residue that must be neutralized.  IMO the liners are more trouble than they are worth.  Unless the tank has been weakened by corrosion I would not use one but if you do follow the instructions to the letter and no shortcuts.

[Bob Wessner]

This suggests 20% phosphoric acid. I used phosphoric acid on mine 4-5 years ago and it created the protective coat, did not flash rust, so not sure what the problem might be.

http://www.krudkutter.com/msds_sheets/MR_msds.pdf

[leaderbean]

Man I do not know what to do.  I used "The Must For Rust" from Home Depot.  Which says on the spray bottle: warning, contains phosphoric acid.  I poured the whole bottle in and swished it around for a couple hours, rotating the tank occasionally to let it sit upside down/on the sides.  I then poured in several gallons of warm water mixed with a couple tablespoons of baking soda.  It fizzed when I put it in and created a gas.  I then dumped it out figuring it was neutralized.  That is when the rust came. 

I have attached a picture of what I am calling rust.  Please tell me it is something else, like that protective coating you guys are talking about.  Is this Zinc Phosphate?  What SHOULD that look like?

Also I took a picture of my chemicals.  I am off to Home Depot to get more acid. 

And man I was freaked to use a gallon of MEK!  I went to school for industrial design and used MEK a few times to glue plastics together.  In school they kept it in this tiny little bottle with a tiny syringe like tip to apply the SMALLEST amount of the stuff.  Our professor made it very clear that MEK is like straight from hell and will instantly destroy your liver if you get it on your skin.  So I had some reservations when buying a whole gallon of the stuff!  Plus it comes in one of those rectangular chemical bottles that sucks to start pouring.  Guaranteed spilling for the first 15 seconds of pouring.  Stupid design.  I also spilled a bunch on my hand the one time I wasn't using gloves.  Who knows what that means.  My liver feels okay and I had a couple beers last night and felt fine. 

Thank you for all the help.

[Bob Wessner]

Certainly looks like rust. What I used was the POR-15 three step kit, first part Marine Clean (degreaser/cleaner) followed by the next step, phosphoric acid. I had planned to go on and use the sealer, step 3, but decided not to since after step 2 it looked like a brand new tank. Still does. I don't know what the difference could be between what you and I used for the acid step. Dilution maybe??

[BeSeeingYou]

I wonder about leaving the acid in for a few hours.  I have never had it sit in my tank for more than 10 minutes.  Is it possible that that stuff is just too weak?  I am just not familiar with it.  The flash rust looks pretty heavy.  Muriatic acid works very well for heavy corrosion (diluted 50%).  Use it outside as the fumes are very irritating.  Gloves and goggles please. As I said before CLR worked very well for me and it does not irritate the hands or lungs if you spill a bit on your hands or get a whiff of it.  One tank I used both muriatic and CLR.  I did not neutralize the muriatic very well and so used the CLR to get out the light flash rust.  One thing I did not mention before was after the acid I rinsed out the tank quickly with just water then used the baking soda.  Less fizzy reaction this way.

[MikeDeB]

With phosphoric acid you don't need to neutralize it.  By neutralizing it you eliminated the acid's ability to create the phosphate coating on the remaining light rust and caused the interior of the tank to flash rust.

Pour the must for rust back in and swirl it around like you did before; for the same amount of time or a little more.  After you have poured the must for rust out of the tank, just rinse it with warm water.  The tank should be ready for the POR-15 coating.

[leaderbean]

Hmmm.  I switched over to the "Phosphoric Prep & Etch" product made by Klean Strip.  More expensive at $14 for the gallon, but maybe it will work better.  It says right on the front that it prevents flash rusting.  I am now documenting everything with pics and will probably make a good "how to" thread if it works.  If it doesn't, I won't make the thread!  

I plan on swishing some diesel around to seal it off because I have read on here that that works.  Correct me if I am wrong.  I never really knew why that would work.  I've read that you can seal the inside from air with WD40, Diesel, Transmission Fluid, the list probably goes on.  I chose diesel cuz I had quick access to it.

Maybe the acid soak time was too long on my last attempt.  I will check on it periodically this time and stop it at 10 or 15 minutes.  The flash rust is completely covering the interior, but it isn't deep.  Just light surface rust.... all over.  

I saw a gallon of Muriatic acid at the hardware store for 8 bucks.  Tempting, but I avoided it because of all the positive stuff I have read on here about Phosphoric acid.  I want that Zinc Phosphate seal.

[leaderbean]

Thank you MikeDeb.  I will NOT neutralize this time around in the tank.  I will return the acid to its original bottle and leave it at that.  If it flash rusts, than I still have the acid. 

[Bob Wessner]

I wonder about leaving the acid in for a few hours.

Good point on the time, I doubt I had mine in there more than 15-20 min. tops, plus no neutralizing, I just flushed it for an extended period of time with water then dried it as quickly as possible with a hair drier and them some paper towel to sop-up the little bit of water that hangs around the filler neck when you invert the tank.

[leaderbean]

It is done.  Success!!  Keeping in mind that I DO NOT CARE ABOUT MY PAINT JOB, My process this time around was:

-Pour in a full gallon of "Phosphoric Prep & Etch" made by Klean Strip and available at Home Depot in the paint section.
-Plug petcock outlet and fuel cap with rubber stoppers.
-Swish acid around periodically for 15 minutes.  Checking inside of tank occasionally to monitor progress.
-Drain acid directly from tank, back into original "Prep & Etch" bottle.
-Set tank in appropriate area and run garden hose into fuel cap opening.  Crank on hi for a couple minutes, letting water flow both out of the top and bottom.
-Add 3/4 a quart of Acetone into tank to absorb remaining water.
-Plug up tank and swish Acetone around.
-Drain Acetone out
-Add a quart of Diesel fuel
-Plug up tank and swish Diesel fuel around
-Drain diesel fuel
-Plug up and let it set till I can paint!!

Here is a picture of the inside before adding the diesel.

[myhondas]

Well,
That looks nice & clean..... I may just do that to my K4 flake orange tank.....

[Bob Wessner]

Looks good and as it is supposed to. Nice job, bet you're happy.

[BeSeeingYou]

Looks great.  I have read posts of people having good luck with this method but this is the first good photo I have seen of the results. I will have to give it a try on my 75 XS650 tank.

[the_saint]

Hmmm.  I switched over to the "Phosphoric Prep & Etch" product made by Klean Strip.  More expensive at $14 for the gallon, but maybe it will work better.  It says right on the front that it prevents flash rusting.  I am now documenting everything with pics and will probably make a good "how to" thread if it works.  If it doesn't, I won't make the thread!  

I plan on swishing some diesel around to seal it off because I have read on here that that works.  Correct me if I am wrong.  I never really knew why that would work.  I've read that you can seal the inside from air with WD40, Diesel, Transmission Fluid, the list probably goes on.  I chose diesel cuz I had quick access to it.

Maybe the acid soak time was too long on my last attempt.  I will check on it periodically this time and stop it at 10 or 15 minutes.  The flash rust is completely covering the interior, but it isn't deep.  Just light surface rust.... all over.  

I saw a gallon of Muriatic acid at the hardware store for 8 bucks.  Tempting, but I avoided it because of all the positive stuff I have read on here about Phosphoric acid.  I want that Zinc Phosphate seal.

i used the same thing on my thank works great. even found a pin hole leak in the tank that was covered with rust.

[fasturd]

Great thread and nice to know how easy it is for the general public to get their hands on chemicals the greenies don't want us to have!



You gota love vintage motorcycles. A total excuse to waste, burn and dribble gas, oil and anything else we can get our hands on!( Not that ANY of us would be irresponsible.)

I have a couple of tanks that are going to get the treatment this week!

[Mille44]

It is done.  Success!!  Keeping in mind that I DO NOT CARE ABOUT MY PAINT JOB, My process this time around was:

-Pour in a full gallon of "Phosphoric Prep & Etch" made by Klean Strip and available at Home Depot in the paint section.
-Plug petcock outlet and fuel cap with rubber stoppers.
-Swish acid around periodically for 15 minutes.  Checking inside of tank occasionally to monitor progress.
-Drain acid directly from tank, back into original "Prep & Etch" bottle.
-Set tank in appropriate area and run garden hose into fuel cap opening.  Crank on hi for a couple minutes, letting water flow both out of the top and bottom.
-Add 3/4 a quart of Acetone into tank to absorb remaining water.
-Plug up tank and swish Acetone around.
-Drain Acetone out
-Add a quart of Diesel fuel
-Plug up tank and swish Diesel fuel around
-Drain diesel fuel
-Plug up and let it set till I can paint!!

Here is a picture of the inside before adding the diesel.

With this method, do you do the POR15 treatment right after the Acetone step if you wnat to finish right away? I have a decent (minimal rust) CB350F tank that isnt going to see service (exept paint/ polish) for 6 months or so and dont want to see a rusty tank when Im ready to reinstall.

[mrbreeze]

I'm doing 2 tanks as I type this. My red one was rusty inside and has been sitting totally dry for years. My blue one was OK but I decided to put prep & etch in both of them. I read somewhere here in the forum that after you drain out the prep & etch you're supposed to mop up whats left in the tank with a towel on a wire hanger. So what do you do after that? Hose it out with water? Flush with something? I was surprised that my red tank turned out so well. I was wondering if it might develop some pin holes but it looks fine. So they are both sitting in the garage...the blue one mopped out and the red one up on end to let the prep & etch pool so I can mop it up. Both tanks look good and I want to make sure I don't screw anything up at this point and have to start over. I am going to run my red tank now that it is rust free so I can do whatever/whenever to it but I got the blue one sold to a member here from Texas so I don't think I should put anything in it that would be bad to ship (gasoline comes to mind!!) It was also mentioned not to put baking soda into the tank to neutralize anything because it stops the transfer of the coating to the metal. Any words of advice for a first time tank derust?

[TwoTired]

As I understand it, and my experience. The phosphoric acid treatment is self limiting.  You apply it and leave it overnight in a humid environment.  It makes a zinc phosphate coating, that itself blocks further metal reaction.  It needs to be rinsed sometime the next day with water, (I use distilled).

It can then be left to dry out.  Or, that can be expedited with an acetone or alcohol rinse.  Last time I did this, I coated with Kreeme after a total dry out.  But now with E10 being prevalent, I'm not sure this coating would hold up, unless you gave it a month to thoroughly and completely dry under a forced air process.

The zinc phosphate coating is sacrificial, in that it is supposed to sacrifice itself to any corrosive attack before the steel can get involved.  Normally such a surface wetted with gasoline would block corrosion of either metals.  However, I just recently learned that Zinc is incompatible/reactive with ethanol.   But, I don't have experience how long the zinc will last with constant exposure to E10.

Knowing that our carburetor bodies have zinc in the metal casting alloy, gives me one more reason to hate being forced to use E10.  One can only hope the blended fuel foisted upon us has another component to delay corroding the carb bodies.

Ethanol is non- reactive to uncoated steel, FYI.

[mrbreeze]

It is done.  Success!!  Keeping in mind that I DO NOT CARE ABOUT MY PAINT JOB, My process this time around was:

-Pour in a full gallon of "Phosphoric Prep & Etch" made by Klean Strip and available at Home Depot in the paint section.
-Plug petcock outlet and fuel cap with rubber stoppers.
-Swish acid around periodically for 15 minutes.  Checking inside of tank occasionally to monitor progress.
-Drain acid directly from tank, back into original "Prep & Etch" bottle.
-Set tank in appropriate area and run garden hose into fuel cap opening.  Crank on hi for a couple minutes, letting water flow both out of the top and bottom.
-Add 3/4 a quart of Acetone into tank to absorb remaining water.
-Plug up tank and swish Acetone around.
-Drain Acetone out
-Add a quart of Diesel fuel
-Plug up tank and swish Diesel fuel around
-Drain diesel fuel
-Plug up and let it set till I can paint!!

Here is a picture of the inside before adding the diesel.

My tanks looked like this last night but wet with the prep & etch. Should I have rinsed it out with water immediately after draining the prep & etch? The way I've heard is not use the baking soda but what about the left over water? Some say acetone, alcohol, and then blow dry or hit with compressed air. I'm thinking I should have rinsed it with water quicker. Here they are after I got back to em today. Should I run the prep & etch through again or what about running a clean gallon of vinegar through real quick?

[2strokeTrush]

little 2stroke oil and heat with a heat gun untill dry.  Worked for me

[TwoTired]

What was the humidity during the drying process?

Prep & Etch says to apply/wet the surface and allow to dry overnight.  Is that what you did?
If you want totally visual rust free, you'll have to retreat?

But if your finger can wipe the rust that you see off the surface, it will also fall off as light powder during use and flow right through the system, maybe even with a rinse with acetone or alcohol.

I didn't get that with my treatment process.  But, I also used forced air (3" fan blowing into the filler neck) to dry out the tank.

[flybox1]

My tank kept its gray phos coating, but after the prepnetch treatment, I thorougly flushed with water, then with a pint of acetone, shop vac hose (flow reversed) put into the filler cap to air dry, then in went 8 oz of MMO, sloshed it around, and then shelved the tank for 4 mos.  Still as gray as it was the day I treated it.  Rinsed out most of the MMO w mower gas and filled it up.
I really suggest a good rinse/dry, and then coating it with something if you're not going to fill it right away.

[mrbreeze]

Yeah it turned out good. I thought you just drained out the prep & etch and let it dry. You have to rinse it out with water and then get the water out. The prep & etch just keeps the rust at bay long enough to remove all of the water and get a protective coating in the tank. I used compressed air followed by a good sloshing with alcohol and another good sloshing with ATF. It looks great now. The directions don't show using it to clean a tank. Just brushing it on to metal. I will use this method again if the need ever arises again. Thanks Lloyd and everyone else that responded to this post.