What are the best methods for grouting (and other grout issues)?
Do you thing there is something I could add to the grout to make it stronger on the edges? I've heard that adding acrylic paint can strengthen it (??)
No, not paint. That's just for color. There are acrylic or latex additives, called admix, which one can mix into dry grout instead of water for enhanced strength. It's sold on the shelves right by the grout. But don't add it to Polyblend brand. It already has polymer additives in it.
If your grout dries too fast, it's probably for three reasons. One, the base absorbed some water. Two, the ambient temperature was too warm, or you were working in the sun. Three, too much or too little water was added to the grout, or it was not mixed well.
I use Polyblend sanded grout with water. I've never done the misting bit, and unless you live in the desert, I'm still not sure why one would. I've never had a single crack or problem, so somehow, I'm doing something right. The last time I grouted, I made mental note of the steps. I call my technique "waterless" grouting, because the only water I use is that contained in a plastic Solo cup, so there is little to throw out, and nothing to hose down. I hope this will be helpful for someone, because it's as frustrating to me as it is to you that you are having problems.
I work at my kitchen table, over plastic garbage liners spread out flat, a big one for the table, and a smaller one for the project to sit on. Wearing a mask, I measure out the dry grout first, about two cups or a bit more. This is a great amount for a birdhouse, a bowl or a medium sized frame with some left over. Into a plastic Cool Whip container, I place about 1/4 of the grout, and spill in a good amount of water from my cup. I stir this very well with a painter's stick. It is very runny and very wet, but absolutely smooth. Now I start slowly adding more dry grout, stirring constantly. As soon as it starts to clump, I know it's time to add more water, a teaspoon or so at a time. This gets it smooth again, and still stirring, I add more grout. I keep slowly balancing water and grout, both in small amounts, until all the grout has been added. I work hard to get this completely mixed, concentrating on the bottom "corners" of the container. My grout is now mixed, and so thick, the paint stick stands straight up in it without support. But it is not dry anywhere, it is thoroughly and evenly mixed with no clumping.
I remove my mask, wait a few minutes, and lift a handful of the grout out of the container and apply it to my mosaic and start rubbing it in. This is the fun part! I lift up my mosaic to get sides, bottom edges of tiles, etc., spreading and rubbing as I go. I lift my mosaic with my left hand, and grout with my right hand only. I am thorough. When satisfied, I wipe grout from my hands with paper towels (those "shop" towels from HD are great!), wipe off the paint stick, pop the cover on the Cool Whip container, shake the fallen grout off the smaller liner, and go outside for a few...