Can you post a picture of your retaining walls? I'm interested too. I've thought about trying a veneer of 'tufa over blue styrofoam cut in a variety of squares and rectangles to face a section of (ugh) vinyl fence. Weight would be a big problem there. You might look up patterns like "Random Asher" which would allow you to make multiples of a variety of shapes in dimensions that would fit both together and leave no waste if you can figure a way to make thin "stones" for veneer. I'm thinking a mixture of Portland, sand and vermiculte with a larger proportion of vermiculite than one might typically use would be light weight. It wouldn't be as strong, but for a veneer that might be ok. You could experiment with adding colors and maybe even doing some layers of two colors (or tones or shades of one color) to make some striated "rocks". The FAQ section has various recipes. Vermiculite has some natural silica stone reflective qualities in some of the pieces. Hope you get lots of suggestions and work something out. David

Thanks everyone for the information, and Tommyc & Simon, I have saved your instructions for a future project. I have been using solar panels with AA batteries to power my LED projects and it seems to be working wonderfully. I really like not having to hard wire stuff. It took me a few tries before I clued into just how bright different LEDs are. The first ones I got were pathetic, and I ended up using some 'mid-range' LEDs. They produce enough light to satisfy the look I'm trying to achieve. Still working on diffusing them somewhat to produce the most pleasing glow, apparently a small amount of silicon over the LED will do that. I also learned that 'yellow' LEDs don't necessarily produce 'yellow' light, but more amber. And that 'yellow' LEDS are actually clear. All very confusing, but once you figure it out it's like having insider information! LOL Must try David's trick of the mylar. Is it clear mylar or silver? Thanks again all! Most helpful bunch here.

S_dreamer, that's the smart approach...I learn everything the hard way :) I'm making a new one that is a lot bigger and rigged with lights. Mark, I was new when I did this, but it's still holding water and in one piece. Someone else may have a better strategy for filling the voids. I tried some of that stryofoam spray, but it's pretty expensive and very messy. The paper inside the mesh was used to keep too much tufa from filling all the hollow spaces (to keep the weight down). The paper around the reservoir was wadded into balls and wired onto the outside of the mesh to make the surface uneven. In either case, the paper is still in there. Good luck with your project!

I've thought about that - does anyone know if it would be considered "to code" by bldg inspectors? That said, it still wouldn't be inherently insulated. Of course, I could add insulation, but then I'm sort of back to the same "non-waterproof" problem. Thx!