You want sanded dry grout. premixed is too runny or whatever and more expensive than hetting dry and mixing your own, and there are very few applications for unsanded grout and its nasty to work with.

I use Mapei sanded grout with polymer on everything. I buy it at Lowes. One caution: the wrong color grout can ruin the look of your piece so take care in choosing the right one. It's hard to say what rules to follow ... It seems to me that an off-white looks good only with delicate colors and styles such as flowered plate pieces, whereas black and charcoal look best with stronger colors, and I like the pale sand color with just about everything. If you already have several colors of grout on hand, you can drop in some dry grout among your tess and get an idea of what the grouted piece will look like.

Azcactusflower: Do you live in a town where they have a specialty flooring store? There is such a thing as "outdoor" grout, used for the application of outdoors, but as to where you live, it may not be as needed as here where I am(rain/freeze/crack) but def sanded, def dry, and you can't go wrong with grey, then add your own color with acrylic paint, I'm saying this cuz you will only need about 2 cups of grout for a bowling ball.> Slow and I buy grout in the 25lb bags now...heh heh!(addicts!). You may or may not wish to seal this, therefore there is grout sealer(also I use outdoor sealer)

CALAM - I buy 50-lb bags of mortar, and as large a bag as possible in grout.... I just got back from Lowes - bought four sheets of diamond lath - gonna begin work on the animal bench/planter similar to the one I worked on in PV that Riana made, and RATS - this reminds me - I forgot to buy mortar - out of gray and only have white. Think I can add some black grout to it to make it gray.