Question on cleaning grout in corner of shower, without damaging tub...

What's the best way to clean the darkened, damaged grout in the corner of my shower without damaging the tub at the bottom? Any ideas on what to use (and how to use it?) Swore we wouldn't let this happen when we redid the bathroom, but here we are. And I haven't got a clue. I want to redo the corners with new grout and sealant, but she fears I'll screw it up. And I keep thinking that if I screw it up, I back up and do it again. Right now nothing is happening, and it's getting worse. Am tempted to take an old toothbruth and some general purpose cleaner (called Method, in a pump spray bottle) and see what that leaves me with. Have some toilet cleaner that is 20 percent hydrogen chloride which I know will probably damage the tub (enamal over steel, or cast iron, looks like), but is there nothing in between these two extremes?
Thanks for any replies. Haven't been here in a while, and would appreciate a measure or two of the home repair wisdom and experience that is know is out there.
Dave
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Dave wrote:

Rinse very well then try white vinegar for hard water issues. Also try google for more ideas.
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There was recently a discussion about this, and someone said you have to use a product containing phosphoric acid to first remove soap scum completely. Otherwise, the soap acts as a barrier which keeps mildew remover from working effectively. I don't recall, but one product mentioned MIGHT HAVE BEEN called "Kaboom", which I've seen in several supermarkets. Stay tuned. Someone will wander in here with more info.
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Chlorox or any mildew cleaner. If it's permanently stained and not too deep you can abrade the grout with a tile cutter and then seal. If it's really deep you can cut the grout out (there are several methods) and re-grout. I doubt anything you're likely to use will damage the tub or tile, but I would stick with things designed to work on mildew. Even though they say not to, I've even used them on painted surfaces without damage.
After you get it cleaned you're going to have to do something to keep the bathroom dry or you'll make a career out of this.

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On Dec 28, 10:52 am, " snipped-for-privacy@att.bizzzzzzzzzzzz"

Pure out of the bottle Chlorox or similar bleach applied with a toothbrush and great care to avoid getting any on your body or clothes as it will bleach them too. Rinse several times, and then apply sealer of your choice.
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On Tue, 28 Dec 2010 09:46:38 -0800 (PST), "hr(bob) snipped-for-privacy@att.net"

It's not all that bad to get on the skin, just promptly rinse it off. Watch the *EYES*, though. A face shield is highly recommended. Forget saving the clothes. Wear expendables.
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On 12/28/2010 11:15 AM, Dave wrote:

Corners should properly be caulked, not grouted. I would use a utility knife to scrape out the surface grout - no reason that I know of to completely remove the grout unless it is loose and crumbly - you will be covering it and sealing it up. Then clean the joint immaculately, beginning with a good household cleaner to remove grease and soap film. Wipe/brush with full strength laundry bleach, let dry, then grout with good silicone caulk. Done. If you haven't done caulking, practice on something else - might be tricky to get a smooth line going across the other grout lines - can use masking tape and take care to smoosh it down into the other grout lines so caulk doesn't ooze under the tape. Remove the tape right away. I've done it with good results and I'm not an expert.
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On Tue, 28 Dec 2010 12:53:11 -0500, " snipped-for-privacy@earthlink.net"

Yes, excellent point.

Let dry == 48 hours. An alternative is to rinse the area down with alcohol, being sure to get it into any cracks (to displace any water). It'll dry much faster.

If the grout is a color other than white, grout tinted caulk is available at tile stores. You can often get very close. Use a wet finger to smooth the caulk. There are also cheap grout forming tools at &bigboxstore.
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Hey all, thank you very much for the input. I cleaned the area with isopropyl alcohol and a somewhat stiff nylon bristle brush, and will do it up right this weekend. Cleaning was all the wife was after for the moment, so she is happy. I am happy cause I now have some idea as to how to proceed from this point forward. Many thanks.
Dave
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