Phosphoric or Oxalic Acid for Bathtub

Hi,
My bathtub is cast iron and 62 years old. The previous owner was elderly and wasn't able to clean very well. It has quite a bit of calcium, lime, soap scum and rust deposits. From reading this group and various other sources I know I need to clean it with acid I'm just not sure which would be better - phophoric or oxalic acid (aka wood bleach). I know oxalic is poisonous and phosphoric is little easier to deal with but I want the best results possible. Refinishers do an acid cleaning before they refinish a tub. Anyone know what they use? I would appreciate any info you may have regarding acid use for cleaning a tub with these kinds of stains.
Also, after cleaning does it make any sense to use a polishing compound to buff out the tub? I'd like to restore whatever luster or life it has left in it and I don't want to resurface. I was thinking of a buffing compound such as what is used on cars after they are newly painted. I believe this has a componenet similar to a very very fine grit wet/dry sand paper. Aren't tub paints similar to what are or used to be used on cars?
Any thoughts would be greatly appreciated.
Please e-mail direct to snipped-for-privacy@sbcglobal.net
Thanks very much.
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Check label on Bar Keepers Friend, Oxalic Acid. You DON'T want to sand it or inhale dust.
On 25 Feb 2004 11:06:47 -0800, snipped-for-privacy@sbcglobal.net (Jen) wrote:

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snipped-for-privacy@sbcglobal.net (Jen) wrote:

Phosphoric acid is the ingredient in naval jelly, and would be good for derusting.

Oxalic acid is a bleacher and would be good for organic stains.

They would use a really strong acid to etch the surface, so the new finish sticks. You wouldn't want that.

Hydrochloric acid, available at the hardware store as muriatic acid, in quarts or gallon jugs, does a good job of cleaning calcium, lime and soap scum. It can be diluted down (do as you ought to, add acid to water) to make your own cleaning solution(s).
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John Hines wrote:

acid is that it converts insoluble iron salts (stains) into soluble oxalic acid salts of iron, oxalates. Iron is about as inorganic as it gets.
RB

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I was incorrect about oxalic acid.
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Oxalic acid works. Barkeepers Friend is one form. Stainless Steel Cleaner is another spray product. But I think dishwasher detergent brushed on and left for an hour works even better.
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Jen wrote:

Phosphoric acid doesn't do a very good job of dissolving lime scale. Citric acid does much better. If you can find someplace that sells it in bulk, it's not very expensive -- I think I paid $5 for a pound of it recently. You can use it with Dawn Power-something dish washing soap and dissolve the lime and soap scum at the same time.
Citric acid will be a lot easier on your lungs than any more powerful alternatives I know of. Sprinkle a little on, rub it in with a wet rag or brush, add a little dish detergent, rub a little more, and let it soak in for a while. Scrub with a brush. Rinse. Repeat.
Best regards, Bob
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I'd consider it more of a scale preventative, intended for long term contact (ie: a dehumidifier).
For scale/rust removal, I'm partial to "Zep" brand "Calcium Lime and Rust" remover, available from HD. Prolly around $5 US per gallon. A small fraction of the cost of CLR, and somewhat stronger.
Active ingredient is hydrochloric acid, but a lower concentration (more in my comfort zone) than hardware store style "muriatic acid" - last time I opened one of those, we had to evacuate the house. [container was prolly >15 years old, and the amount of HCL gas that escaped was phenomenal...]
--
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Jen wrote:

For soap scum, try a razor blade scraper first (at least on the flat areas) to get the major crud off. Then scrub with 3M pad and full strength Dawn dish detergent to get the rest of the soap scum. Then use CLR (calcium lime rust) on the lime. If the glaze is eroded away and the iron exposed, go easy in those spots.
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Jen wrote:

True. Oxalic acid is poisonous but you'll find it in spinach and coffee, to mention a couple of foods that have reasonable amounts. Just be careful working with it. Remember the DOSE is the poison.
and phosphoric is little easier to
For removing calcium build up I'd favor phosphoric acid (which can also be a nasty acid). Gloves and eye protection are in order.

I'd imagine that they use hydrofluoric acid to etch the porcelain. Of the three acids this is highest on my list of dangerous acids. You can get some nasty burns with HF.
I

Be very careful that you don't abrade the porcelain.
I'd like to restore whatever luster or

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Jen wrote:

Cast iron isn't painted (normally). It is porcelanized which means it is heated and small glass particles are applied; they fuse (melt) and coat the surface.
None of the chemicals you mention will attack a porcelain surface so once you get the crud off it should be in good shape. If you *do* need to use an abrasive, try it on a small, inconspicuous place first because many are hard enough to scratch the porcelain surface...you don't want that.
-- dadiOH _____________________________
dadiOH's dandies v3.0... ...a help file of info about MP3s, recording from LP/cassette and tips & tricks on this and that. Get it at http://mysite.verizon.net/xico ____________________________
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In article < hi Jen
Have you thought about using a pumice stone. Takes a little elbow grease, but it works and is non toxic.
linda
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You might try an automotive rubbing compound, or polishing compound (finer texture).

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