Phosphoric Acid part 2

General Discussion. Make yourself at home...read, ask and answer!



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PostPosted: Mon Jun 29, 2015 7:22 pm
I don't use phosphoric acid that much but when I do I will saturate a rag or wash cloth and lay it on the rusted panel. then cover it with visqueen and masking tape and let it set for as long as needed. this way it doesn't dry out making clean up easy and it works much better.
Jay D.
they say my name is Jay



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PostPosted: Wed Jul 01, 2015 6:32 am
timmm wrote:hows this plan sound :

1) sand the surface rust/treated areas with 80grit
2) REACTIVATE the treated areas with phosphoric acid and steel wool, and try and remove as much rust as possible from the pitted areas. when i finally get everything nice and shiny, proceed to wash the treated areas with dish soap and plenty of water.
3) dry the treated areas with blow drier
4) apply primer
5) fill pitted areas with body filler/glaze

one more question regarding the Primer:
the local paint-supplies-guy sold me an Acrylic primer, should i use it? or is an epoxy-based primer a must?
tom


I was hoping someone familiar with your products would answer your question on primer, but here in the US, we like to use epoxy primer on bare metal.

Your plan looks good, except after step 3.
The acid will smooth out (to some degree) the 80 grit scratches you put on before the acid, so I would go over it again with 80 grit on a DA, then clean and dry again before applying epoxy primer.

ScottB wrote:No, I did not have the coarser steel wool saturated long enough to dissolve it, why would or could I? This is not complicated. Urinate on metal long enough and it will eventually dissolve. Pick your acid. Sub out your labor intensive processes and have cars blasted to save time for all your restoration jobs. If you have a commercial blasting system then you are better off yet.


Derusting the roof in the link you posted took 3 hours, and it was a very good example for phosphoric acid use, and that is time enough to go through a few wads of steel wool. Red scotch pads are usually on hand, and I seldom have a need for steel wool any more and don't even keep it around.



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PostPosted: Wed Jul 01, 2015 6:37 am
timmm wrote:hows this plan sound :

1) sand the surface rust/treated areas with 80grit
2) REACTIVATE the treated areas with phosphoric acid and steel wool, and try and remove as much rust as possible from the pitted areas. when i finally get everything nice and shiny, proceed to wash the treated areas with dish soap and plenty of water.
3) dry the treated areas with blow drier
4) apply primer
5) fill pitted areas with body filler/glaze

one more question regarding the Primer:
the local paint-supplies-guy sold me an Acrylic primer, should i use it? or is an epoxy-based primer a must?
tom


I was hoping someone familiar with your products would answer your question on primer, but here in the US, we like to use epoxy primer on bare metal.

Your plan looks good, except after step 3.
The acid will smooth out (to some degree) the 80 grit scratches you put on before the acid, so I would go over it again with 80 grit on a DA, then clean and dry again before applying epoxy primer.

ScottB wrote:No, I did not have the coarser steel wool saturated long enough to dissolve it, why would or could I? This is not complicated. Urinate on metal long enough and it will eventually dissolve. Pick your acid. Sub out your labor intensive processes and have cars blasted to save time for all your restoration jobs. If you have a commercial blasting system then you are better off yet.


Derusting the roof in the link you posted took 3 hours, and it was a very good example for phosphoric acid use, and 3 hours is enough time to go through a few wads of steel wool.
It makes a mess and is frustrating using it for this purpose, red scotch pads are usually on hand, and I seldom have a need for steel wool any more and don't even keep it around.

But results are the important thing, and there are a number of products to do the things we do, so there are many different ways to get to the same place.



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PostPosted: Sat Jul 04, 2015 8:29 am
thanks chevman, bobby and badsix for the suggestions.

picked up a can of epoxy primer the other day, along with a pretty big scotch bright pad(green, but seems way more coarse than the green ones found on dish sponges.)

at the moment am busy with other stuff, but hope to pull the fenders and try doing the repair within the next 10days.

chevman: i think that i'm going to have to try an pull it off without the ZEP, because it isnt available out here. i guess i can try a local brand engine degreaser if you think its necessary? But like i mentioned in an earlier post, i've got about 1L of isopropyl and a can of W&G Remover. i plan on using the W&G(good scrub with nylon brush) , followed by the isoproply(apply via small brush thoroughly and then wipe down with a clean rag) prior to applying the primer. since i can get ahold of ZEP, any other tricks for preventing flash-rust?


thanks to all
tom



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PostPosted: Sat Jul 04, 2015 7:02 pm
They say that after rinsing, if you put alcohol on it that will help get it dry quicker. I never tried it, but it makes sense to me. Then after you towel dry it off, use plenty of compressed air.



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PostPosted: Fri Jul 10, 2015 5:41 pm
Hey guys.
Tried the phosphoric acid steel wool/ scoth brite pad today, and was pleasantly surprised with the results. I did the job by hand(my thumbs r killing me), but was able to convert the surface rust into nice shiny metal, however the pitted areas are not turning shiny, but rather, they've turned black. i was thinking about picking up a wire-wheel brush attachment for my drill, and then reapplying the phosphoric acid and then try and clean out the pitted areas with the wire wheel. Should i give this a try? Or can i leave the pitted areas as they are(black) and move on to the next step? Are the black pitted areaS rust or has the phosphoric acid converted the rust?

If need be, i can upload a pic a little later.

Any advice would be appreciated.
Thanks
Tom



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PostPosted: Fri Jul 10, 2015 7:39 pm
timmm wrote:Hey guys.
Or can i leave the pitted areas as they are(black) and move on to the next step? Are the black pitted areaS rust or has the phosphoric acid converted the rust?


Tom

If you use something like this

Image


to scratch the pits, the black will quickly turn to rusty brown, and that is why I always get rid of all the rust. If you are not blasting, then just keep scratching the rust in the pitted areas with the pick, and rewetting, the wire wheel will have a hard time getting in there.



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Joined: Tue May 19, 2009 7:10 pm
Location: OREGON COAST
PostPosted: Sat Jul 11, 2015 10:28 am
^^^^ Yes apply more acid and pick and wire brush until CLEAN.
Jay D.
they say my name is Jay



No Turning Back
Posts: 977
Joined: Mon Jun 20, 2011 3:58 pm
PostPosted: Sun Jul 12, 2015 6:43 am
double post
Last edited by chevman on Sun Jul 12, 2015 7:29 am, edited 2 times in total.



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Joined: Mon Jun 20, 2011 3:58 pm
PostPosted: Sun Jul 12, 2015 6:46 am
timmm wrote: was able to convert the surface rust into nice shiny metal, however the pitted areas are not turning shiny, but rather, they've turned black.
If need be, i can upload a pic a little later.

You should not forget Scott's advice about the rust being more than surface, and that has proven to be true.

ScottB wrote:
I have a feeling the surface rust on that Mercedes is deeper than you think. It is probably corroded between or behind the panels/pinchwelds and is now coming through. No amount of topical treatments will stop it, it has to be cut out and repaired correctly.


I checked that Mercedes model, and it doesn't look like they have a wheel opening molding, so the rust is probably worse on the inside and the seam.

Even when the rust is just on the outside, it may not look like it to someone new to this, but if one of those rust pits have even a very small hole all the way through, or if there is rust at the seam, then your efforts will be in vain, because you can not get to the back side to clean all the rust and treat the metal.

When the rust pits are kind of deep, its hard to tell about holes without a light shinning on the back side. If the rust pits are indeed minor, then a course wire wheel at slow speed with plenty of pressure on it may work, but a finer wire wheel will only polish the rust and make you think its all gone. After using a wire wheel, apply more phosphoric acid and that will tell you if it is shiny metal or just polished.
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