[aphocks]

Hello all, I am slowly building a CNC Mill about 12x10x5" in size. I would like to use aluminum extrusions as they offer me the most flexibility because I intend to modify the build as I go, and change out linear rails, spindle, and ball screws later. I want more rigidity though so I would like to fill the frame with concrete where I can. I don't want o fork over the money for epoxy/sand/granite that's why I'd like to use concrete. Problem is that concrete reacts with aluminum, so I was wondering if anyone has tried coating their extrusions in clearcoat spray, thin epoxy layer, or something else to protect the concrete from the extrusions? Here's the rough sketch I have, but I am working on a more professional drawing as I get in parts and measure them correctly.

The blue is concrete and the gray is aluminum, I used 4" PVC pipe as a filler to reduce the concrete needed without reducing damping/strength much.