Why Won't Grout Seal?

I recently re-grouted my bathroom shower and am having problems getting the grout completely sealed. It seems no matter what I try, the grout still absorbs water. Not only does it look bad when wet (color darkens) but I am sure the re-grout job will not last long with it constantly being wet. Here are some particulars that may or may not be important:
- The problem is worse on the floor, where there are 2 1/2" square tiles. The walls, with 4" spuare tiles, have the problem in some areas but parts of the walls are also perfectly fine. Parts of the floor are fine, for that matter.
- I have tried about every type of sealer I can find. The first type I used was TileLab SurfaceGuard, which I think is a penetrating type. This appears to have been the least waterproof any all the types I used.
- The old grout was white. I re-grouted with an off-white sandless.
- I only removed the old grout as deep as needed. Where the grout was in relatively good shape, I only remove a little depth with a grout saw - just enough so the new color would be uniform.
Did I do something wrong?
Thanks!
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Yes , patching grout has never worked for me. Removal and complete reinstall is the only thing I have found that works. I use a cordless saw and a diamond blade. I use a dremel with diamond blades for the corners and small spots..
Makes one hell of a mess.
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If the grout is hard and wont scrape off the job is good, dont worry unless it falls out or is soft.
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Personally I don't do re-grouts because they are always questionable at best. Grout is made to go in- between the tiles and lock in underneath them. When you re-grout, you're only trusting in a thin surface bond. A complete removal as SQLit mentions would be acceptable because the grout could get deeply into the joint to grab.
I don't know why the tilelab stuff didn't work. For floors I use the darker, expensive ($15 pint) bottle of Tilelab and it seals polymer grout in one heavy coat. You can dump water on it when dry and it beads and will not soak into (or darken when wet) the grout.
I've also never sealed shower tile. For one, it's hard to get the sealer to lay on it long enough to dry, because it's a vertical surface. Secondly, I have a personal problem with all that moisture and running water getting into the grout, yet not being able to dry out because the sealer is holding the moisture in. I know sealers are supposed to be "breathable" but by the way they make water bead on the surface, I question how much moisture can get out of damp grout. I don't use darker colored grout in showers for the reason you mentioned. Pure white (sanded or unsanded) will not darken when wet and looks great with any tile in a shower. At the most I use a light-to-medium color that won't darken so bad, and warn customers in advance that it WILL darken. I like to just do a good job grouting, and leave it unsealed in wet areas. Moisture and water are not bad for grout.
I sealed a floor area real well (20 x20 porcelain). Later it flooded for a day and the people told me it took weeks for the grout to dry out. My opinion is that the water got under the sealer and into the grout, and took a l-o-n-g time to dry out.
All this is my opinion of course...
thetiler
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