Styrofoam is used by many cement & concrete sculptors as a base for their work. Start by building up a few layers of plaster wrap...the same stuff doctors use to build up casts. Most large hobby stores carry it these days. Then apply about an inch of a 50/50 cement/sand mix over the whole thing. Once that sets, you can use standard or latex modified grout to adhere your mosaic. I've seen similar pieces scaled up to several feet in diameter and they hold up very well. I've even seen a concrete "sofa" made using the same technique.

Ringo and the Beatles...."I would like to be, under the sea, in an octopus garden" Great! Here is a link that might be useful: Ringo of the Beatles song Octopus Garden

Yes, you can add paint or even concrete stains to add color to grout. The key is to make enough grout in the first place, because if you run out, it will be nearly impossible to make more to match. To get around this, I buy pre-colored grout in the most popular colors that I tend to use most often, like black, grey, or terra cotta. I've also painted the grout afterwards. Depending on the color you choose, it may take two coats. Just wipe off the excess that may get on your glass globs or tile as you go along. Use an acrylic water based paint. I like Patio Paints because they are especially made for the outdoors, but regular craft paints work well too. I always seal my grout afterwards, no matter if I paint it or not. Prevents algae and stains from forming.

What an amazing collection of people make up this group, curious, witty, and thoughtful. Thank you all for your friendship. cnm1 - I first drilled eight new 1/2" diameter holes in the ball, bent and fitted the rebar, mixed about a Tablespoon size dollop of Bondoî, and attached two legs at a go. (By fitting two legs at a time it kept the ball balanced). The insulator was done in a similar fashion: I drilled a pilot hole for a 3" lag bolt, fitted the insulator, filled with a small quantity of Bondoî, and it was basically complete.