It sounds like it might be too wet (too thin). If the grout lines are too sunken in, and you're not causing it by wiping off too much at the wrong angle, then the liquid in the grout may be getting absorbed into the substrate, causing the grout to sink. When you wipe off the excess grout, you try to go at an angle across the grout line, not along the grout line. But I know you know all this already. Try mixing the grout thicker (less water) and try again. You can grout right over an already grouted piece once the first try has set up. Come back and let us know what you figure out.

I KNEW you would answer !! LOL That must be the problem ... grout too wet. I imagine when the damp sponge goes over it again & again , it'll pick the grout right back up and Plus,it's being absorbed from underneath. Such a simple solution & I never thought of it !
That goes to show you --- NEVER STOP LEARNING .

**** I'll regrout tomorrow , I bet it will turn out perfect.

THANK YOU !!!!!!!!!!!!

In addition to what Silvamae said, I don't do much wet sponging. I grout rather thick and always smoosh it on by hand. I let that dry for a good 20 minutes then I go over that with a wet sponge squeezed as dry as I can get it. I only use grout sponges--I've tried others and they don't work well. When I go over the grout with the sponge, I'm actually filling in those little imperfections, the dips and holes if there are any. But at this point, I'm not trying to get the tiles clean. I'm just smoothing it all over more than I was able to do by hand. I let that dry for another 20 minutes or so and from that point on, I use painters towels (the torn rags you buy in the paint section for a buck a bag). I found if I try to do the whole thing with a wet sponge, I start taking too much grout off. The towels will clean the tiles without affecting the grout lines too much.

Don't know if any of that helps, but that's what I do!

Loribee -- That helps alot ! Thank you ! I think that's another thing I'm doing wrong -- I don't wait long enough to wipe it off. I'm using a rubber float to wipe my grout off , it should take the grout off at the glass level .
Now I see !!!!!!!!!! You've both taught an old dog new tricks :) LOL

I never used Mapei. I have some but too chicken to try to use it. I do know when I used non sanded grout I got air bubles in my grout lines.

I cheat on cleaning my grout and just wipe with dry paper towels. Then buff with old bath towels cut to rag sizes.

I usually wipe it all on with my hands in a thick consistency.I let it set a short time and do a gentle wipe off. Then let it set longer and wipe again testing how well set up the grout joints are. I have never tried a grout float. Maybe I should.

Silva,
Really, I can go over grout that's set? I was always told I couldn't do that, so I've never tried. Does it matter how long the grout's been set? You've inspired me to try it, because I have a piece where there's some imperfections in the grout and it makes me absolutely crazy. This is music to my ears! I'll let you know how it goes.
Thanks,
Becky

No, it doesn't matter how long it's been set.

Here's another thing or two you can do with grout. Let's say it is dished out or there are pinprick bubbles, or hairline cracks. You can mix up another little batch, grout over the problem areas, and then, after carefully wiping the grout, you can gently pat the grout. Yes, using a damp sponge, you can softly pound the grout into submission. This gets rid of bubbles and fills in cracks.

Also, at the end of the process, before the grout sets up, if you have a little area that just isn't right for whatever reason, you can brush the grout with a wet cosmetic brush. For instance, the grout around the base of a flat marble; you want it flat, not mounded up. You can dig out the excess, then take your makeup brush, dip in water and shake out, and carefully smooth around the marble. When I go to a garage sale, I look for those little Estee Lauder makeup brushes and that's what I use for final touches on grout. One more thing, after the grout has completely set up, but before you seal it, you can sand it - like on the edge of a picture frame or table, where it's a little lumpy, just sand it smooth with a sanding pad.

The one thing I've never been able to correct is if I colored the grout and then need to do a touchup and try and match the color. It's always off. So I never color my grout; I use it as it comes from the bag and then I sometimes paint it. When I paint grout, I never use a brush; it doesn't look good. I use a cosmetic sponge and I dip into the paint, then pat onto the grouted piece. Then I wipe the tess off while trying not to wipe off the painted grout.

Silva,
You are a font of information! Thanks so much for sharing.

I tried your methods in my last grouting session and they worked beautifully. I thought I had to get the grout off the tess right away.

I didn't realize there was so much time to deal with imperfections.

The 20 minute interval between wipings made it so much easier because of the firming up.

Many thanks for the information. Susan

We never stop learning. Mosaics is an on-going learning process.

And you've all just answered all my questions!
Thank you