He is right. Regular spray bomb primer works and looks OK, but it will allow moisture to pass through. If you do not have the ability (compressor - spray gun - etc.) to spray epoxy primer, I highly recommend the Eastwood Epoxy spray cans. They cost about $20 each, but they are a good alternative. Then have a vial inside the can that releases the hardener when you strike the bottom of the can. No mess, no fuss, and no cleaning the spray gun when you are done.
