Here you will find instructions on the way I have made silicone caulk molds and 2-part mother molds. I have learned the silicone caulk mold-making method from NOFU on the Hypertufa Forum and thank him as well as Rickharmer for their inspiration and information!
The two-part mother mold part I must have gotten from osmosis. It works for me. Please feel free to alter these methods to suit your particular project. If you have any questions or suggestions that will make things easier, or, if I have omitted any steps, please feel free to contact me at buckyforce@earthlink.com
And now, drumroll please.. How to make a silicone caulk mold from a master (the item you are hoping to cast.) Please forgive me if I repeat myself or give too much information. I plan on creating these instructions for the newest of casters. So, without further ado...
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This is a planter foot which I will call the "master" for the rest of the tutorial. Coat your master with a good paste wax, (car, furniture, Butcher's Wax, a couple of coats. No need to buff in between, we are just creating a barrier or "release" between the master and the silicone we will be applying. This particular master has a lot of grooves (his mane) that we need to make sure are adequately coated so that the silicone will not stick to it, without removing the details. After coating, pick the master up and in a good light, look it over. You will easily see if details have been missed as the wax leaves a dull sheen to this highly glazed master. If your master is dull, i.e. cast concrete, close your eyes and let your fingers do the work. |
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Project needs:
GE Silicone I or II - depending on your budget (clear silicone. I have used white for this tutorial but find the clear more flexible and forgiving - I know not why) Liquid glycerin - check with your pharmacy Acrylic paint - any color A syringe or eyedropper - pharmacy supplied, no needle required - your vet has them too! Flexible putty knife Tub to mix in. A 1 qt. yogurt container is perfect! A caulking gun - not shown - sorry! |
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Cut the caulking tube on a wide setting, about half way down the nozzle and push the entire tube of caulk into the mixing tub. The wider the opening the more caulk you will push out, and faster. |
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Now, add 4-6 drops of glycerin, and one drop of acrylic paint per ounce of caulk. A standard tube of caulk is 10 ounces, so count as you go. A drop or two extra is not going to make a big difference, so don't worry. |
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The addition of acrylic paint in the mix is
to let you see that all elements have been thoroughly mixed when a uniform
color is achieved. That's my guess anyway and it seems to work. Mix and work quickly. Depending on your location (I'm in South Florida) time may well be of the essence! |
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Start applying the mix as soon as possible. Apply the first coat as THIN as possible as the only down-side to this method are the inevitable trapped air bubbles on the surface of the master. If you can mix short batches, i.e. 1/2 tube of caulk/glycerin/paint mix, at a time using the ice-cube treatment, which follows, to force the caulk into every crevice in an effort to eliminate the bubbles - great! Patience IS a virtue! Once your first coat is on and cured you can slather subsequent coats on as these extra coats are for strength. |
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This is AMAZING! Once you have applied the
first layer of caulk mix to the master and while the caulk is still wet,
take an ice cube and rub it over the silicone. You can manipulate the wet
caulk mix in any direction you wish. Force it into crevices, smooth it, push
bubbles out, whatever. The water will in no way affect the cure. You can
also use the ice cube method to make the entire mold nice and smooth on the
outside should you anticipate making a mother mold. The pictures to the left
are of the outside of the mold while it was wet and after I had smoothed it
with an ice cube. Not necessary but... Add more silicone until your mold is 3/8" - 1/2" thick, paying attention to the bottom edges. This bottom edge is what you will grab to remove your cast and may tear if too thin. You can add cheesecloth or gauze to the just applied wet caulk mix anywhere on your mold, corners especially, that may need reinforcement. Cover with more mix. After all layers have cured, gently remove your mold from the master. This is where all your patience and attention to detail while applying the wax will pay off. Once you remove the mold from the master, if you see any thin spots, you can always add more caulk to the outside of the mold straight from the tube. |
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Making a 2 part mother mold
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You will need:
• Plaster of Paris ("POP") • Gauze or cheesecloth & scissors • Mixing bowl & spoon • Water • Saran or any cling wrap |
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Place your cured silicone mold over your
master. and put them both on a flat surface. I have used a piece of
plywood with a heavy duty garbage bag as a wrap. Neither silicone nor the
Plaster of Paris (POP from here on) will stick to this cover. I have drawn a red line down the middle of the master which will be my guide when I apply my pop-laden gauze. This will make sense in a minute...I hope. |
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Cut the gauze or cheesecloth into medium
sized pieces. If you cut them too small, they tend to get distorted when
full of the POP and can be difficult to work with. I only use small pieces
to fill in sparse areas after most of the mold has been covered. These main
pieces are approximately 10" long and just as they come off the roll of
cheesecloth, probably a triple thickness. I am using cheesecloth, but will be calling it gauze from now on. |
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Put about 2 cups of dry POP in the bowl and add water while mixing. The POP should be about the consistency of well-mixed sour cream. Silky and shiny. If it is too thick, the mix will start to set up rapidly and be impossible to work with. |
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Now, pretend you are in the 4th grade and are making papier mache. This is pretty much how you are going to be using the gauze/POP. Completely soak the gauze, both sides, working it to get it saturated. Hold it up, use your fingers to sort of squeegee off any excess and fold over one long edge about one inch. |
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Take this folded edge and apply it along the guide line you have drawn down the mid-section of your mold. Repeat this process until the entire one half of the mold is covered, gently rub, pat or smooth as you you apply to make sure the gauze fits snugly to the mold. Fill in any gaps with smaller pieces and if you like, extend some of the gauze out from the bottom, on to the table, creating a flange. |
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Congratulations! One half of your 2-part mold is finished. Now, go relax, have a cold one and wash your hands while it sets up. This will take anywhere from 20 minutes to an hour, depending on your weather and how many cold ones you have on hand. |
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When the first half has cured, gently remove it from the mold. Sometimes this can be a little difficult but be patient and work the edges little by little all the way around. It WILL come off. Sometimes they pop right off. Take your time. |
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Place the separated first half on the table and cut a piece of Saran or cling wrap at least 2" larger than the inside of the first half and place the saran inside the first half. |
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Place the first half back on your mold and
lay the saran back over the first half as shown. The reason for this is to
create a thin barrier along the centerline. When you apply the POP to the
second half, you will get an almost perfect match to the first half without
the second application adhering to the completed side while curing.
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Now repeat the process for the second half,
placing the folded over POP/gauze tight along the edge of the first,
following the edge of the first and not the line you first drew. We want
these to pieces to meet as tightly as possible. Cover the second half, as you did the first. Almost finished! Go relax while this cures. Once cured, remove the 2nd half as before, and remove the saran wrap and place both halves back on the master mold. |
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In order to keep your two parts together when you cast, and depending on the size of your mother (mold), it may be necessary to attach hardware along the midline. This can be achieved by the use of a nut and bolt and some homemade loops. These can be made out of coat hangers or any stout wire, as shown. |
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I usually apply these using 2-part epoxy.
When you are ready to use the mother mold simply bolt them together as
shown. The bigger your mother, the more you should use. You will see when
you place the two halves on the master mold, where the mother wants to
separate. Place the loops there. Once this is finished, remove the mother, take your master out of the silicone mold, place the silicone mold back in the mother, secure the bolts, place up side down on a bed of sand for support and cast away! Note: If your sand is damp - at all - place a plastic bag down over the sand! Damp sand will soften the POP. If you have made a flange on your mother, you can use this to make sure your mold is plumb by placing a bullet level on all sides and across the middle. This way, your cast will be level. |
Have Fun! I hope these instructions make sense. If you have any questions or if any of the above is not clear, please feel free to email me at buckyforce@earthlink.net