Over the past few weeks Esther and I have been working on the 1:12 Tudor house she's building. She wanted a stone floor in her kitchen, and I suggested we try egg carton stones, as I'd been saving egg cartons for about a year :)
We had three different colours of egg cartons, and cut a variety of rectangular pieces from them. Esther started laying stones in the middle of the floor and worked outwards. This meant a lot of cutting and fitting around the sides, but it wasn't terribly difficult. ''
When all the stones were glued in place, then we added weak washes of three different colours -- dark slate grey, light grey and raw umber. The egg cartons are VERY absorbent, of course, so there's no open time for this layer. If you want to be able to work your glazes at this point, I'd suggest sealing the stones before you do your colour washes.
Then Esther sealed the floor with three coats of satin acrylic medium -- you could use varnish. She'll play with the stones a bit more (maybe adding grout lines) but I think it looks pretty darned good!