Suggestions Please..........

Using blue or pink foam, you can adhere it to the tables edge with about a half inch of it extending over the top of the table height. Score it, paint it and detail it to simulate a block wall. the ballast is trapped against the base of the wall and you have a nice effect at the table edge.

Jim has carved score lines into the foam and gotten a really nice effect. You can probably find some photos of this at my house, which is code for not providing a link to outside this forum.

If you are willing to put a few bucks into it, buy a couple of lengths of Woodland Scenics "Pennsy Stone" wall. Cut it into strips four or six block lengths high.

Park a green Jaguar E-Type nearby for added realism.  

Since your base color is black I would suggest black silicone down the crack cutting a very small opening in the tube. Dip your finger in water then run it over the top of the silicon bead to smooth it out even with the rest of the area. If your intention is to run the ballast out to the very edge of the board I would use 2in masking tape on the outside of the board sticking up slightly on top to act as a dam. When pulling the tape away pull it on a downward angle from the top. Do this before the glue sets.

Either the silicone or the Durhams will work fine. Some people even simply masking tape the cracks with success. It only has to be for the relatively short drying time and then it's no longer important as the glued ballast becomes the visable finish.

Bob

As a additional insurance, you might wish to put down a baking tray.. something a foot wide by two feet on the floor with a plastic hefty 30 gallon bag over it to protect the general area. It's only just for this spot and should ensure no messies.