Grouting Help

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Old 02-05-13, 05:59 PM
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Grouting Help

My shower wall has a couple of small sections (2-3" long) where the grout has fallen out. It seems like the installer was a little sloppy in these spots and didn't fill in the gap completely, but the rest of the grout is fine. So now I'm trying to mix a little bit of grout to fill in these gaps, but I'm having trouble.

The tiles are all less than 1/8" apart so I'm using unsanded grout with a polymer additive from Lowe's. I used just enough water to make a peanut butter like paste, waited 10 mins for the grout to slake, then remixed and applied the grout to the wall. After letting it dry for 15 mins I used a slightly damp sponge to clean up the lines and remove excess grout. I then waited 48 hours before touching it again.

After all that the grout is chalky to the touch and if you wet it it becomes putty-like and can easily be removed from the wall with a toothpick. Originally I thought my mixture must be wrong, but all the leftover grout in my plastic cup became solid as a rock and has none of these problems.

Does anyone have any idea what I could be doing wrong? My only thought is that maybe it's drying too fast on the wall. It's winter and I'm sure my forced air heat has driven the humidity down. I've never worked with grout before but it seems to dry up really quickly on the wall (10-15 min) while the grout in the cup takes at least 6 hours to dry out. I guess it's also possible that I'm using too much water on the sponge, but I've tried to be very careful about that.

I've failed at this 3 times now so any advice you could give me would be appreciated.
 
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Old 02-06-13, 03:38 AM
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This is from the Tile Council of North America:

Grout packed after cement hydration started. All cement based materials have a pot life. Iif water is added to the mix after the grout begins curing in the bucket, the grout will be sufficiently plastic to pack but will not cure into a hard homogeneous block - rather it will be crumbly and weak.

Try decreasing the amount of time the grout sets in the bucket before applying to wall. I mix mine as dry as possible and I usually immediately start sponging the joints working in small 4' x 4' areas. The immediate sponging provides additional moisture as I go. Usually unsanded grout, while messy, is fairly easy to work with. If unsuccessful, try another brand of grout. The grout may have sat on the shelves a the box store too long.
 
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Old 02-06-13, 06:40 AM
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If this shower has been in use with grout missing it's possible the sides of the tile have become covered with mineral deposits or soap scum.

And a bit to what czizzi posted. Grout is a cement product. It hardens it does not dry out like paint. It's a chemical process that is activated and needs water to happen. The grout needs to stay moist until the hardening process is complete. If the grout mix is too dry and put onto a dry porous surface it can loose it's moisture before it has a chance to bond or develop sufficient strength. If tiles or stone are unglazed & porous I will sometimes wet the tile before applying. You don't want puddles or a sheen of water but you do want the tile or backer to have the darker look of being wet. So I sometimes mist or spray with water about 5 minutes before applying.
 
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