|Project by GnarlyErik||posted 10-05-2012 07:46 PM||4219 views||12 times favorited||6 comments|
I like working in my shop and my wife enjoys working in our yard. She recently decided to expand our patio by casting her own concrete pavers. We bought some plastic molds at Lowes, but they seemed a bit limited, so she asked me to make custom ones for fitting in odd places.
Using 2×4 stock to match the thickness of the plastic molds, I’ve made irregularly shaped molds for our pavers. When direct casting into a mold you must allow for getting your piece out of the mold. The usual way is to build ‘draft’ into the mold, and you do this by tapering the sides about 5 degrees or more so the casting comes out the wider side and does not bind to the mold.
In this instance, acrylic caulking was used for filleting material at the join between the sides and the bottom (which becomes the ‘top’ of the finished casting). Then, using a heavy latex paint the bare wood was coated. When that dried, a spray-on bed-liner type rubber coating was applied. Concrete likes to bind and stick to things, so a mold release agent must be used. For concrete, spray on Pam works well, or kitchen vegetable oils, diesel fuel or almost any oily liquid.
If you want to decorate your casting, it is easy to use a quick hardening acrylic caulk to make a design, pattern, or even a name – much as in cake decorating. Modeling clay and many other materials work well too. You must make your design ‘reversed’ or a mirror image for it to come out as intended. Acrylic caulk may be scraped off your mold, and a new design easily applied. Simple molds may be made for casting in many mediums other than concrete such as plaster, thickened epoxy, body filler putty, fiberglass, etc. Many mediums cure through an ‘exothermic reaction’ wherein the mixing of the materials produces its own internal heat. This is why concrete may be poured in cold weather. Some mediums like fiberglass and epoxy can produce lots of heat – and even catch fire.
If you decide to try casting, research your medium well before attempting your casting!
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