This section is an addendum to the Stepping Stone Manuals, and contains information which is more easily accessed when separated from the general manuals.
The Working Superplasticizer Solution
Melamine Superplasticizer powder must be dissolved before use. The essential step in doing this is to agitate the liquid continually as the powder is very gradually sprinkled in. It’s helpful to have some sort of mechanical mixer like an old electric cake mixer, a blender or a small drill-attachment mixer. Use 1 ounce of water for every tablespoonful of superplasticizer. This allows for the substitution of 1 ounce of solution for each tablespoon of superplasticizer required in a formula. The solution will last for several weeks, but I don’t recommend that you make more than you plan to use in about a 2 week span. Calculate the amount you will probably need. Example: to make a 14″ stone you will need 4 tablespoons of “Superplasticizer”, which equals 4 ounces of the solution (4 oz water + 4 TBS superplasticizer). If you plan to make 4 stones this size, you will need 16 ounces of solution (16 OZ water + 16 TBS superplasticizer).
Measure the amount of water into a plastic container. Start the agitation before adding the powder. Sprinkle powder in very slowly while agitating constantly. Continue mixing after it is all added until the solution clears and turns a slightly pinkish color. There should be no lumps if the procedure is followed properly. If lumps are present, remove and discard them (these will NOT dissolve again in your concrete mix). Use is easy if you keep the solution in a plastic pouring bottle or container. Keep tightly covered during storage and at room temp. The superplasticizer will not re-solidify once it is well dissolved.
Pre-dissolved Calcium Chloride Solution
It’s very convenient to make a Calcium Chloride solution in larger batches in advance. You won’t need to wait while it dissolves or cools. The only trick will be to control the concentration of your solution so you’ll know how much to use. That’s very easy. For every cup of water, add 1 cup of dry CaCl. This yields a 100% solution in which 1 cup of the liquid equals 1 cup of the dry. If you need less, just add liquid to match the dry cup measurement as stated in the formula. The batches can be made for several stones or saved for later use. CaCl is an inorganic compound and is fairly stable in solution. I’d try to use it within a few weeks, so it isn’t wise to make it by the GALLON. Don’t use a metal container for mixing. Mix and store in plastic, tightly covered, at room temp. MIX well or shake just before use.
If you fill stone molds completely by over-filling and screeding the surface, you’re in danger of producing lips on the edges of the finished stone. Lips are those annoying little flanges of concrete that remain on the bottom of an unmolded stone. There are ways to prevent them and ways to get rid of them. I’ll give you some advice from a great stone-guy who wrote in response to my question about these.
Method #1 – Conc. Man’s Solution
“After you pour the piece and screed off the excess, take a thin plastic spatula and run it vertically around the edge about 1/2″ deep into the piece. This action pushes the aggregate away from the edge and allows the cement cream to fill that space. After the initial set and surface appears dry, run the spatula flat around the perimeter, along the edge of the mold, pressing the concrete down from the screeded surface about 1/8″ to 1/4″ and by doing so, creating a slight bevel. Run it around several times to bring up the cream in the concrete, effectively filling the edge and compacting the surface. This may be all you need to do. Use the spatula or a trowel to flatten the ribbon of cream generated by the tooling of the edge. As the concrete gets firmer the tooling will be easier and look cleaner.”
Method #2 – Angel’s Solution
I’ve tried Conc. Man’s technique. It’s tricky. First time I did it I was left with a trough all around the edge of the stone…but no lips. Next time I just screed and wiped all the concrete off the mold edges. I used a spatula to push the concrete mix back toward the center of the mold, bringing up a little cream as it was moved. That worked and it’s what I still use. I believe you have a right to both techniques and use the one that works. With experience we all seem to do something instinctive, because the lips problem disappears with time and a few people never see it.
Method #3 – Under Filling
I don’t like under-filling molds. A thinner stone is a weaker stone, but this is another method used to prevent lips. I do notice in glass studios where they’re done that none of the stones seem to be the same thickness. It’s no doubt the result of under-pouring by the “seat of your pants”.
As for the existing pieces with lips, you can grind these smooth or even put a slight bevel on them. Use a coarse, hand-held grinding stone or lacking that, a coarse concrete or clay brick would do a decent job. Wait a day or two after they are poured so that you don’t grind too much or chip out aggregate.
Unmolding With Heat
The Heat Trick
If, for any reason, you have trouble unmolding a stone because the mold was under-lubricated, or the gods forbid, you forgot to use a mold release, here’s a trick to help. Invert the stone onto 2 dowels as usual. Wring out a couple of kitchen towels in HOT WATER and lay them across (and down the sides) of the mold bottom. Use your hands to work the edges of the mold until the stone drops free. Heat makes the plastic mold softer and more flexible. You can get the same effect by using a hair dryer to warm the mold.