Regrouting bath tiles

The tiles on the wall for the bathtub are getting old looking and some of the grout has black stains, likely from mold. Scrubbing lasts a week or so before the aged condition reasserts itself. Its a long time (25 years) since I last put them on and cannot remember the tricks to the trade. I'd like to do as little work as possible since there are so much more other "renovation" stuff I have to do too.
First do I need to remove the grout and regrout? Or can I just apply fresh grout over the old? Only a few spots here and there have lost a little surface grout of flake thickness. This flake thick loss is not visible after I clean them.
Can I scrub clean the whole wall and apply some form of polish then a sealer to restore the tiles? If so what brands should I get? My water supply is very hard and I think the dullness is from the film of soap-mineral deposits.
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I should let someone more experienced answer but Im going to venture and say its best to remove the grout and regrout it. Possibly you could avoid doing it all and instead only where you deem it necessary.
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When my grout starts getting dark from mildew, etc, I clean it as best I can with bleach and tsp, using a firm brush. Then I make a watery grout mix and spread it on like normal with a grout float. I let it dry, then wipe with a damp sponge, then a dry towel to polish. Not only does the grout look like new from the thin new layer, but the tiles shine like new as well.
k

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k wrote:

That's an excellent method of 'freshening' up the grout..
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PaPaPeng wrote:

I had a similar problem, & thought I would need to regrout. However, in my case the grout was only a few years old, which would have made regrouting more difficult. I'd sealed the grout, but a small water leak caused surface rust stains from water coming up from under the grout.
It turns out there are a number of products for "refreshing" grout that put the color back in. The cleaning products didn't work for me at all, although I used them to hopefully provide a better surface to work with.
I just did it this weekend, & it looks wonderful. I have no idea how long it will last. However, the grout was white, & I bought a white pigmenting product. If I did it over, I think I would use a coloring agent to darken the grout, not make it light again.
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