How do I get rid or surface rust on a bathtub?
 

What chemicals should I use? CLR isn't budging it.

What chemicals should I use? Steel wool or an SOS pad or any other pads? "CLR" hasn't done a thing.

Hopefully you didn't strip the shine from the porcelain using CLR.

You need Iron Out
Super Iron Out®

Down here the sell it at Walmart. It's in the laundry/cleaning section. First damp the rust area. Then pour the grains on there and add a little water to make paste. Let is sit there for a while. You might want to use a tooth brush after a bit.

It stinks, but it works in about 5 minutes.

Try Whisk Rust Stain Remover. Works great!

If none of those things work, use a scotch-brite pad. We use the rust colored ones, but they are the most abrasive. Start rubbing lightly, with water, only on the rust spots, then rub harder as necessary. After removing the stain, if it has dulled or scratched that spot, use buffing compound (again, only on the spot). Rub it in, circular motion, then wipe it clean. Should be like new. If the tub is fiberglass or acrylic finish, be very careful, as the dullness and scratches will show much more than on porcelain. (Refinishers secrets)

If you're talking about a reddish brown stain where water drips out of the faucet and onto the tub, then you can use a fairly strong hydrochloric acid as well. The "enamel" on your bathtub is actually quite resistant to harsh chemicals like acids, alkalis and solvents, and hydrochloric acid shouldn't harm the enamel. (Check in an inconspicuous area to be sure, though, if you want.) Any hydrochloric acid based toilet bowl cleaner will dissolve that rust quickly, I'd expect.

However, don't let the acid get on any chrome plated bathtub drain flanges. Hydrochloric acid of toilet bowl cleaner strength will also eat chrome plating.

If you're talking about repairing rusting chips in the bathtub enamel, post again.

I've never tried it, but heard it works - Coca Cola and some tin foil

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