Here goes:
1) buy the polystyrene at lowes or home depot. It comes in a package of 5 or 6 sheets. Usually in the insulation dept. Only costs about $5 & will make A LOT of fake rock! So you only need one package.
2) Pick up the cheapest grout you can find. I use the big 50 lb bag because it is only $10. I also get the kind with sand in it, although you could add more if you wanted. There is a lot of different colors to pick from, pick what ever floats your boat.
3) Get some grout sealer. I buy the kind in the yellow bottle. About $8- $12. Only need 1 bottle, follow the instructions on the bottle.
4) Get 1 tube of liquid nails the kind for projects.
5) break or cut the styrofoam into shapes you like, make adjustments before you liquid nail them together or grout!
6) Liquid nail the pieces together, let dry for 30 minutes or so.
7) Mix the grout according to instructions, make the 1st layer runny & paint it on to get all the cracks filled in. Make the 2nd layer thicker & paint it again after the first coat has dried. If you want you could go thicker or add even more layers.
8) seal the grout with grout sealant per the instructions on the bottle.
This is what the fake stuff looks like while coat one is drying.
