The easiest way to pour into uneven and round-bottom molds is to place them into a bed of level, moist sand. This technique will support the sides and hold the mold level until it sets. You should still cover the poured molds with plastic to aid the hydration process. And don't forget to use mold release in the mold itself to aid in stone release.
Or, as the photo above illustrates, you can use a sheet of plywood and make a "Die Cut" of the set of molds being used. You can do this with a jig saw after penciling the design on the plywood. This method is best for production work, or if you will be making a lot of the same stones from the molds.
If you want to get varied coloration, you can sprinkler in some powdered colorant, shake it around a bit, and dump out any excess. Experiment with some different color combinations and techniques until you get the results you are looking for. Sprinkle colorant on top of your concrete
mix prior to scooping up the mix to fill the molds, as well.
Be sure to visit our "
TECHNIQUES" article for more detailed instructions on coloring.
Filling Your Rounded Concrete Molds Using the Sand or Die Cut Methods.
EITHER TECHNIQUE WORKS WELL. IT'S USUALLY A MATTER OF PERSONAL PREFERENCE.
USING THE SANDBOX TECHNIQUE FOR FILLING ROUND BOTTOM MOLDS:
I suggest you start by building a "sandbox" out of 2"x4"s. Fill it with fine sand and level it off as much as possible. What I do is use the level edge of another 2x4 to screed the top of your box. Basically, you over-fill the sandbox with sand, and then run the 2x4 along the top edge of the box to smooth and level the sand within. You will then have a nice level sand base to start with once you do this procedure. Note the handles on the sides of the sand box. These are to make moving the filled boxes around easier.
For just a couple of mold pours, you may want to consider using a small "pile" of sand. You can put a level across the top of the mold after setting it in the sand to be sure it is level. Using a sandbox makes the leveling almost automatic though.
Before you begin your pouring session, dampen the sand slightly to give it a bit more body. You may want to push the molds gently into the sand to create a cavity before filling the molds with concrete. This will facilitate a faster and easier insertion of the mold once it is filled with concrete and vibrated.
Push the mold into the moist sand. Pour the concrete mix into the mold. Lift it out of the sand so you can vibrate it a bit to release any bubbles, and to compact the solids to the face of the stone. Re-insert the mold into the sand cavity, and level. Cover all of the poured molds with plastic sheeting once filled to aid hydration and the curing process. Leave them undisturbed for at least twelve hours, depending on the temperature. If you are not in a hurry, leave them undisturbed for a minimum of 24 hours or more. The longer you leave them in the mold and covered with plastic%u2026 the stronger they will be, and the easier they will be to demold. Leaving the stone in the mold for a few days does not present a problem either, and is actually beneficial. Visit our Squidoo Lens on "MAKING CUSTOM STONE" for more in-depth information about making concrete stone and tile.
If you have a number of molds, and are doing a number of pours, you may gently lift the molds out of the sand once they are hard, (a few hours), and you can then pour additional molds using the same sand cavities. Be sure the concrete has hardened sufficiently though. Stack the filled molds (gently) and cover the stack or pile with plastic to aid the curing.
MAKING A DIE CUT-OUT FOR FILLING ROUND BOTTOM MOLDS:
Another option is to build a frame out of 1"x3"or 1"x4" lumber to hold each of the various size molds. Basically, you build a "box" that the mold will fit into, but which allows the mold edge to lay on top of the frame to help support the mold. I like the sand system better, and it is actually much easier once you get used to it.
One big advantage to the frame system though is that you can stack the molds on top of each other as they are being filled. You can also vibrate all of the molds in one rack together. A piece of plastic between each layer seals the heat and moisture in, and aids in the hydration and curing. Obviously, it is your choice though.
When the stone is ready to extract from the mold, lay it face up on a flat surface. Apply slight pressure to the mold edges, and the top of the mold. Do not push in too hard, or you may crack the mold edge. The stone will usually drop right out of the mold as you lift the mold off.
, or demolding, be sure to cover the stone with plastic again. This will aid in the curing process. You DO NOT want to "dry" your stone quickly. Keep it wet for as long as possible, as this procedure will give you a much stronger stone.
After installation of your stone, you may want to apply a penetrating sealer such as our Olde World StoneKote Sealer. This will help protect it, waterproof it, and help in freeze-thaw environments. You may also use a matte or gloss sealer if you desire, in lieu of the recommended "flat", or "non-sheen", natural stone finish.