I started over on the rock wall. Using contact cement I glued all the boards together creating three large blocks that I then carved. I took my time on this one and let it set for a day.
Once everything was carved up I mixed a sloppy batch of cement to do a scratch coat over the surface of all the pieces. Tools are handy... on larger projects, I just wore gloves and applied it all with my hands.
Next up, I'll mix a heavier batch and probably color it and add some sparkle for a heavier coat. Once it sets a little i'll carve it out and shape it. I have masonry sealant for when it's all done and dry.
Oh, I painted the back wall of the 55 gallon also.