RUBBER MOLD CARE AND POURING TECHNIQUES
continued
Line up your molds in a convenient spot for pouring. Place molds without legs (shells or bird bath tops) on wooden or cardboard pads rather
than directly on a concrete floor. Many different types of cement are available and you should experiment to find out what suits you best. Stone
is important for a good concrete mix, therefore if you are using sand without stone it should be added to your mix. Three parts crushed stone to
two parts sand works good.
Your concrete mix should be three parts stone, two parts sand, to one part cement. Mix dry items together first if you are using a wheelbarrow.
Add water and mix alternately.
When using a cement mixer put items in, in this order: Water, chloride, sand/stone, then cement. If you are adding chloride, we suggest a
handful of calcium chloride per mixer load of cement.
The consistency of your mix should be such that the cement mixture just pours easily from a gallon can into your mold.
Extra vibration of a few seconds is okay, but longer is not necessary and may cause the stones to settle to the bottom.
If large quantities of water come to the top of the mold after vibration, you may be using to much water in your mix. If air holes are apparent in
the finished product, try adding more water to your mix or pour your mix into the mold a little slower allowing vibration to remove air bubbles as
the mold is filled. Leave the cement heaped up in the center as this will allow the excess water to run off and allow for settling. If your mold has
vents (straw like projections) gently prod them with a blunt wire to encourage water and air to come out. On very large molds you may want to
clamp off the vent before pouring as the cement may leak out. Long reinforcing rods should be jiggled to remove air pockets. Reinforcing can
be put in simpler molds at this time, this way you can be sure wires stay centered instead of being vibrated over to the side.
After cement has set for about an hour or thickened up some, scrape off the bottom with a trowel. Bird bath plugs can be put into cement at this
time. If bird baths have a thin bowl bottom you may want to pull some of the cement to the middle for extra thickness where the plug goes,
rather than scrape it off flat. Molds should be allowed to set undisturbed for 24 hours after being filled. In cold weather it will take longer, up to
48 hours.
MOLD REMOVAL, CLEAN UP AND CONCRETE CARE PROCEDURE
When concrete has hardened the appropriate length of time, turn molds over and remove bolts with a reversible drill or hand wrench. Pull the
fiberglass pieces off, then strip the rubber off. If the rubber does not fall away from the concrete easily, you have left the concrete in the mold
too long. If the fiberglass pieces come off easily, but the product breaks, the concrete should have been left in the mold longer. If a fiberglass
piece comes off with difficulty, use mold release on the OUTSIDE of the rubber next time you pour. If that doesn't solve the problem you may
have to sand the spot on the fiberglass that is catching, these are called undercuts. Your new molds need a breaking in period, don't expect
the first one to be perfect!
After stripping your molds the rubber part should be spread out over the fiberglass pieces to dry, but not in the sun. The rubber should be dried
several hours when new, after aging a few weeks the drying time can be cut down. After drying, spray the rubber with mold release, forcing
mold release into the cement clogged vents also.
Wipe out any dirty spots with an old cloth, although rubber needn't be spotless. Now push a wire through the vents, pushing out the cement
plug. Previous spraying with mold release will have loosened it up.
Your molds will now be ready to put back together. Reassemble the pieces with the rubber inside, lining up the seams carefully. Put the wing
nut assemblies back on with your reversible drill or hand wrench.
Most rubber molds leave practically no seam lines, but you will want to remove any ridges of cement that you can find. Use a file and do the
work while the concrete is still green so that it removes easily. If the concrete is allowed to harden, seam removal will be more difficult.
Any patching that is necessary should be done at this time. If you wait until the concrete has dried out you will have to dampen the piece and
keep it damp for several hours while your patching material dries slowly.
A suggested patching material is Acryl 60 and cement powder, mixed to a toothpaste like consistency and apply with a damp brush or fingers.
Allow the concrete to cure in a damp spot out of direct sunlight. Covering with plastic to keep in moisture works very well.
Your concrete product should dry 7-1 0 days before you paint. This time may vary depending on the type of paint you use.
