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A:
It depends on 1) the type of mold rubber you
are using as your mold material and 2) the make up of your
concrete ad mixture.
1. What mold rubber are you using?
Silicone rubber has the best release properties, but will
succumb to the abrasive effects of the high-aggregate
content of the concrete and lose detail over time. It’s
best to use a concrete release agent like Smooth-On’s In &
Out to protect the mold.
Urethane rubber does not have great release properties to
begin with, so a release agent is recommended from the
start. Note; Our customers find that, even without a
release agent, high aggregate castings will release from
VytaFlex molds after the mold is "seasoned" - used to cast
concrete 10 - 12 times with In & Out Release Agent.
2. Ad mixtures:
High sand content ad mixtures generally release easily and
do not require mold release from either silicone or urethane
molds.
High aggregate ad mixtures will not release easily and will
even bond to a urethane mold.
In & Out Concrete Mold release offers the following
advantages; a) it will release concrete castings from the
mold, b) it will not harm the mold, c) it will not stain
your concrete castings and d) will not interfere with
concrete pigment.
Do Not Use: Concrete casters try different release
concoctions such as vegetable oil or petroleum jelly, but
these materials will destroy the rubber mold over time and
may stain your concrete.
What If I Don’t Have In & Out Concrete Release Agent? Until
you can get some In & Out, you can try dishwashing soap and
water mixed at 10 parts water to 1 part soap. Rinse the
mold with soap solution and immediately cast your concrete.
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Smooth-On