Originally Posted by vtdiy
And if the rails are aluminum extrusions then steel (and copper plating) and aluminum "don't mix" either if you're worried about corrosion. On the other hand since it would be internal to the rails, mortar wouldn't cause any more problems that BB's, unless you like to work under water.
Mortar and (presumably) wall plugs for things to screw into on a machine tool?
The epoxy would isolate the steel from the alloy, no corrosion issues. Mortar etches alloy on contact, and chances are it will end up on an external face no matter how careful you are, as well as shedding aggregate through any mounting holes.