There are a few ways to to seal
Regular spackle or joint compound, like that used in repairing walls and
drywall can be spread on top of the foam and textured.
A product called Durham's Water Putty, a
plumbing material can be used with great success. It is sold in most
hardware and home improvement stores and is relatively affordable. A 5 lb.
can can be purchased for about $5-6 and will last quite a while. It is a
yellow powder that should be mixed in 3 to 1 ratio with tapwater. It
should be mixed in small amounts as it dries rather quickly and will dry
or cure to a rockhard finish in 24 hours. It can be applied with a putty
knife, plastic picnic type knives and spoons and wooden stir sticks also
available at paint supply shops. It can then be drilled, carved, cut as
DO NOT DUMP IN SINK. This material will
damage your home plumbing by blocking your pipes. The best way to dispose
of unused Durham's is to allow it to dry in the mixing container and then
be discarded as you would any household trash or garbage. This is why the
best mixing containers are plastic drinking cups or old plastic tubs like
you get with yogurt or butter.
This also is an extremely dusty material and should be worked with in a
well ventilated area, outdoors and optimum safety can be assured with the
use of a dust mask also available at most aforementioned stores for an
inexpensive cost. Remember that you can't put a price on your health.