RUBBER MOLD CARE AND POURING
TECHNIQUES
from Nunnikhoven Group
PO Box 580
Mediapolis IA52637
1-800-356-4632
Take your molds apart when
you receive them and coat the rubber with mold release inside and out. Use of mold release
on the outside of the rubber will help the fiberglass slip off easily. Use mold release on
the inside of the rubber before each pouring and on the outside once in a while as needed.
Use of mold release makes a much smoother casting, keeps the rubber clean and lengthens
the life of the rubber.
YOUR MOLD RELEASE
MIXTURE SHOULD BE AS FOLLOWS:
One part commercial grade castor oil
to 8 parts methanol or denatured alcohol. We recommend this mixture on your molds, any
other type of mold release may damage the rubber. Never use petroleum products on your
molds.
The rubber part of your mold should fall
away from the concrete easily. If it sticks to the concrete you have left the product in
the mold to long or more castor oil is needed in the mold release mixture. Forty-eight
(48) hours is the maximum amount of time concrete should ever be left in the mold,
especially in warm weather.
Cement build-up on the rubber usually means
too much castor oil in the mold release mixture. This can be removed from the rubber by
soaking it, a SHORT time, in a mixture of one part muratic acid to six parts water.
Muratic acid can be ordered through your local drugstore or swimming pool supply store.
Let the new rubber part of your mold dry
thoroughly between pourings - several hours. The rubber will not dry inside the fiberglass
casing, but should be spread out or hung up in a dry spot. Never dry rubber or pour molds
in direct sunlight. New molds may swell or stretch if not dried well. After the molds have
aged they can be poured continuously without a problem.
A pressure sprayer works perfectly for
applying mold releaser t puts on a fine even coat and is completely portable.
Fiberglass molds without a rubber liner can
be used the same as metal molds. Mold release should be a form oil.
The quickest way to remove and put on the
wing nut assemblies is to use a 3/8" reversible electric drill fitted with a
1/2" nut driver.
The wooden legs on your mold should be
periodically inspected for damage. Legs may sometimes be loosened or cracked during
shipment and may go unnoticed until the mold is filled with cement. Nunnikhoven Group
cannot be responsible for accidents or damage caused by broken mold legs. Fiberglass molds
without legs (bird bath tops, for instance) should be placed on cardboard or plywood
before vibrating, as constant vibration on a concrete floor will wear holes in the
fiberglass.
If you experience stickiness, swelling,
blistering, stretching or tearing of the rubber mold liner, you are improperly caring for
your mold or it is showing signs of extreme age. Complete, step by step instructions on
mold pouring follow. The instructions are aimed primarily at the beginner who has never
poured a mold before. As you gain experience you will develop shortcuts, but don't
sacrifice quality for speed!
CONCRETE POURING
PROCEDURE
Prepare your molds for pouring by following
the directions in the general mold care section.
Reinforcing rods or wires should be placed
in the molds as you put them together after cleaning. Simple molds may have their wire or
rod put in after pouring. Wires should be fairly flexible and about 1/8" thick.
