It doesn't matter if you use a slotted base, coin or Renedra base, they all work the same. Using any craft glue, apply a liberal amount to your base and sprinkle on the coarse material. Then place one or two chunks of the sprue.
Once thoroughly dry, paint it all with a coat of black.
Add heavy coat of dark grey...
and then a coat of medium grey.
For variety we glued on some grey medium ballast...
then applied a final drybrush of light grey.
There you have it, nice and easy. The same technique works for basing any terrain piece you might build.
Have a Great Battle
The Old Crow