Para-dichloro-benzene (urinal deodorant cakes) only requires about one
tablespoon
of ground-up PDB for each super; and gaseous PDB is HEAVIER than air, so it
is best
to put 3-4 tablespoons in the TOP super if they are stacked.

The normal use is stack supers about 10 supers high placing one tablespoon of
PDB
on top of the frames of each super, with more on the top super.  Seal all the
gaps
between supers with masking tape.  Check monthly during warm weather for
presence of solid PDB, and renew when necessary.

I have used ground up urinal cakes for years and have never had any wax moth
damage.  Just make SURE that the urinal cakes you select are made with PDB
and not
naphthalene moth balls are some other chemical.

I hope that I have helped.

George Imirie
EAS Certified Master Beekeeper
Beginning my 70th year of Maryland beekeeping
Author of George's PINK PAGES