I have mosaiced a styrofoam ball a few months ago. I covered it with thinset first. Then mosaiced it. Its still holding up fine. I'll post a picture as soon as I get my camera back from daughter.
Bianchi.

i was going to ask what kind of glue for gluing sm.tiles on styofoam.

I'm interested in hearing the answer to this question, too. I've never glued directly to the styrofoam - have covered it with a thin layer of concrete. But I thought some had mosaicked directly onto the styrofoam. Also wonder if the size of the object might make a difference - and whether it is indoors or outdoors? Good question, D3bbi!

I had no problem gluing to my swap ball. Prior to that I had seen this at Maryland mosaics

Here is a link that might be useful: polystyrene bases

I have glued directly on styrofoam with silicone, no problems here.

I did a couple this summer. Silicone straight on the styrofoam..no problems

Thanks Nice I wondered where those little forms came from..never worked on styrofoam before myself ,but want to.

I am going to chime in and ask a question too.
I always think of Styrofoam as the coarse "holy" stuff and polystyrene as the compact shiny stuff.
I would think the latter would take substrate, but can the coarse stuff take it also without a layer of thinset,etc?
( I melted it with paint once!)

I've made stuff on all kinds of styrofoam and just use my silicone right to to it! Here is a cake I did using 3 layers of styrofoam, it was fast and fun!!!

Here is a link that might be useful: {{gwi:129659}}

The buoys I just finished were made on polystyrene and I simply used GE II. Worked great.

Meadel, i'm not sure if she was talking specifically about that "fuzzy" one, but Crystal said that she melted an egg she was doing and learned that if she coated it in a weldbond wash first, then she could use silicone (I hope I got that right) with no problem.

Thanks you, everyone, for sharing your experiences. I didn't have time today to check on it. Might have to wait a few days before I get to play glass.