Last Revised 06/21/2004
Ingredients and where to get them. If you’re unable to get the fumed silica and superplasticizer, just try your stones with the remaining ingredients only. You’ll still have a better product than the powdered commercial product or builder’s pre-mixes. If you use white Cement, you’ll be able to get glorious colors in your stones. Cement, Sand and Acrylic liquid are best obtained locally. Shipping would be very expensive.
This manual is designed to answer the queries from people who wanted to learn about Sonafrank’s formula. Knowing ingredients is good. FINDING some of them is another story. Included are my personal formulations for 3 sizes of stones, which will allow you to interpolate and extract the proportions for any size (refer to the “Other Methods” for a technique to measure the amount of mix needed for any stone). Also included are some of what we call the “Hard Knock” hints for learning concrete/glass construction. Mistakes are the best teacher.
Aggregate for stones is sand or crushed marble (pool mix) (WE don’t use gravel in single step, poured or indirect stones). Sand should be very fine (ideally #70 grade), white or light in color and most importantly, washed (clean). PLAY SAND is not the best product. It’s usually brownish and coarse. Cole has recently added pea gravel to his list of ingredients. I don’t use it, but we trust that he sees some use for it. I consider it non-critical and optional. Aggregates are usually sold in 80 to 100 lb bags.
Cement in a pure form comes in gray and white. The white form is harder to find locally. I spent about a month looking for it until I found a builders’ supply that serviced stucco and swimming pool contractors. Buy it in 100 lb bags. Store it in airtight Rubbermaid (or the equivalent) tubs. At $9 per 80 or 100 lbs, it’s cheap enough to discard it if there’s ever any evidence of clumping. Don’t use cement once it’s become damp or lumpy. This means that there has already been some chemical reaction with moisture in the air. Your stones will probably be crumbly or will not set. If you don’t feel a warmth from the reaction when cement is mixed with the liquid ingredient, you probably have bad cement. Turn your cement over with a shovel or trowel in the storage bin. Don’t always use the top layer. If you can feel tiny lumps… DISCARD IT! Store it in a large Rubbermaid tub with a plastic tarp between the lid and the cement. It will keep in a good container for a year or more, even in a non-climate conditioned space.
Acrylic Admixture is best used in the liquid form. It can be the plain acrylic or a mix of Acrylic and Latex. Home Depot and Lowes or other home building suppliers all sell it as Acrylic Liquid Mortar Additive. Home Depot has a 5 gallon can for around $30. This may not be available in all areas, but try these places first. The mixture form is much less expensive and works quite well. Almost all of the liquids contain about 25% acrylic solids.
Calcium Chloride … I got it from a local building supply that sells to concrete fabricators. It came in a 25# bag and wasn’t all that expensive. If you buy it online, either dry or in solution, it would be kind of high cost for such a grossly cheap substance. Look for it locally or try specco.com online. Some Stoners have good success using the “Closet Dri” product. Remember that CaCl is an OPTIONAL ingredient in stones. You can omit it and simply wait a bit longer for a set.
Fumed Silica is also known as Aerosil or Cabosil. I get it online from fiberlay.com. Costs about $15 a pound, fills up this HUGE box and is hilariously lightweight (duh….one lb). I get people to HELP me by moving that box, pretending that I can’t manage it, then stand there and laugh when they nearly throw it into the air. I know, cruel.
It’s used in Fiberglass fabrication (like boats) and in mold making, (Burman mold making supplier online also sells it). It’s used as a filler and thickening thixotropic) agent which is essentially the way we use it in concrete. If you have any of these industries locally, you might want to beg them to sell you some. If not, call Fiberlay. They sell in it that small amount where many people only sell large amounts. The most I ever use is 1/12 to 2 cups and it goes a long way. BE CAREFUL not to breathe it in. Wear a mask before you open the bag because it’s so light that it sort of floats up at you.
Since it’s made of silicon dioxide, you DON’T want to get it into your respiratory system. It adds tremendous strength and density to your stones. For every piece of aggregate, you’re adding 100 particles of fumed silica. WEAR A MASK until it’s well mixed into the dry ingredients and you add some liquid to dampen the whole thing.
Superplasticizer … Get ONLY white, melamine-based (high range water reducer)
There is also a dark form (often liquid) of this that’s made from naphthalene… You don’t want that. Superplasticizer is expensive to buy, but not to use since we only need a small amount. Acrylic liquid, considering the volume used, is THE most expensive ingredient. I have been asked to give you my terminology for the bad stones people have obtained with the Naphthalene form of Superplasticizer. They take forever (usually not ever) to set and wind up soft like “GUMMY BEARS” instead of concrete. I’ve had maybe 100 sad reports of this phenomenon in the past years. I can only tell you NOT to buy Superplasticizer in the liquid form (which is the only form sold by concrete suppliers locally). I don’t want people to be so frustrated and disappointed. When I got my Superplasticizer, I just bought a 20lb tub for $85 + shipping from specco.com (they call it W30-M). You might want to get together with some other stone artists and share the cost. To be honest, I found one other place that would sell it to me retail but only in a 55lb bag. It only cost about $98 but the shipping price just about made up the difference. If you got about 5 people together the price would be worth it and at a use rate of only 6 to 8 Tablespoons in an 18″ stone, 5 lbs will probably last longer than your stamina in making them. If you plan to go commercial, the cost is well worth the results.
I consider this ingredient to be most important for strength and smoothness. You wind up using less liquid and you NEVER see any water or liquid rising to the top as your stone sets. That adds greatly to the strength. It lets you make a smooth, pancake batter consistency mix which requires no “topping” mix. Just pour it into the mold over your glass. There are one or 2 places online that sell it in small amounts. Find them with a search engine or ask about this on the Stone Forum here.
Nylon Fibers are definitely better than other types (polypropylene) and don’t cause a “hairy” problem in the finished product. I get the ConTrol type of 1/2″ fibers from nycon.com. They come in little 3oz bags and you might need to buy a minimum # of them. I think I got 10. Price is around $5 a bag.
Pigments in hardware stores tend to be dark and boring. Delphi Stained Glass has a beautiful assortment of blues, greens and all colors in 3oz or 1lb sizes. Blue, green and yellow cost more, but are well worth it. I got some of the plum color and have used it over and over in the past months until my family is beginning to think I’m color-blind. Love that color! Be sure to make your concrete mix about 2 shades DARKER than you want it to finally be.
It fades during the curing period. I find this especially true of Terra Cotta. Then, again, if you’re making a full-surface cut glass and only have the edges, sides and grout lines showing, it won’t be as much of a problem.
If you want a mold release agent that lets your stones literally drop out when they’re inverted, get 20-VOC (Crete-Lease) from cresset.com. I hear that they now sell it by the 2 lb can. Probable price is around $6.
Now, most of these companies don’t sell direct online. You need to find what you want on their sites and CALL them on the phone (Ph#’s are listed on the home page). Even if you don’t see the product, call anyway and ask. All had 800 numbers. Browse through Cole Sonafrank’s Mortar Materials section. All of these are listed there with direct links.
I’ll give you my formulations. It’s a good place to start. You will notice that there is about a 2 cup cement + 4 cup sand difference between stone sizes. I usually add an extra 2 cups of sand for the pot, as Mom used to say. The amounts of Acrylic Liquid are only ESTIMATES. You should start with a couple of cups and add more gradually to the desired consistency. Remember to go slowly if you’re using Superplasticizer since it takes about 5 min to “kick in” and you’ll wind up with a mix that is too thin if you add a lot of liquid before that happens. I get perfect results with these formulations, but if you find that your set times are vastly prolonged, try cutting down on the Superplasticizer.
REMEMBER that the strength of concrete is DIRECTLY proportionate to the ratio of cement and water. Too thin mixes produce weak stones. Too thick produces crumbly, rough stones. THIS is why Superplasticizer is so vital to the high-end results we want. It lets you get a smooth, thinner mix using less water. Hence, you get a very smooth stone that is still very strong.
It helps if you make some “cheat” cards with your formulations for all the sizes so math isn’t necessary every time.
14″ ROUND STONE
- Cement: 5 CUPS
- Sand: 10 – 12 CUPS
- Fiber: 4 TABLESPOONS
- Fumed Silica: 1 CUP
- Superplasticizer: 4 TABLESPOONS
- Calcium Chloride: ½ – 2/3 CUPS
- Acrylic Admix (liquid): 5 – 7 CUPS
16″ HEXAGON STONE
- Cement: 7 CUPS
- Sand: 14 – 16 CUPS
- Fiber: 6 – 8 TABLESPOONS
- Fumed Silica: 1½ CUPS
- Superplasticizer: 6 TABLESPOONS
- Calcium Chloride: 2/3 to 1 CUP (less is better)
- Acrylic Admix (liquid): approximately 7 – 8 CUPS
Here’s the formula for an 18″ stone. It’s only 1 cup larger than the hex because the stone is actually 18″ at the points. Beautiful for tabletops.
- Cement: 8 CUPS
- Sand: 16 – 18 CUPS
- Fiber: 8 TABLESPOONS
- Fumed Silica: 2 CUPS
- Superplasticizer: 8 TABLESPOONS
- Calcium Chloride: ¾ to 1 CUP (less is better)
- Acrylic Admix (liquid): approximately 8 – 10 CUPS
OK, now for the helpful hints born of hard experience (otherwise known as mistakes) some of which have also been covered in Part 1. They are repeated for context and emphasis.
1) ALWAYS dissolve the CaCl in water. If you add it dry, you’ll wind up with mottled, spotted colored concrete as it cures. That and the superplasticizer diluent is the the only plain water I use. Let it cool before use. It gets pretty warm during dissolution.
2) The Acrylic liquid will make the stone more “flexible” (if you can say that concrete is flexible) and it bonds better with the glass. I don’t measure it exactly because in the humidity in this area it’s always different. The amounts I gave you are approximations, so start with part of that and add more as your mix comes together. It’s like making biscuits. You could make cheaper stones by using 1/2 water and 1/2 acrylic, but I haven’t tried that. I LOVE acrylic.
3) Nobody really measures Fiber. We just sort of take a BIG pinch and call it a tablespoon.
4) Mix the dry fumed silica into the cement/sand/fiber dry mix. Be prepared, because it’s like nothing you’ve ever worked with…sort of like it’s alien matter.. Just be persistent until it seems to hide in the dry stuff. Wear that painter’s mask when you work with this ingredient OR with cement, at least until it’s wet. When you open that bag it sort of wants to float up… looking for the Mother Ship. Put that mask on before you open the container!
5) Superplasticizer needs to be agitated constantly till it’s dissolved or you’ll wind up with a plastic ball. You can make a large batch in advance and it’s stable for weeks. See the “Tips and Tricks” addendum for this method. I use an old kitchen hand-mixer. Some people claim that you can just let it sit in water and eventually it will dissolve. I haven’t got the patience to do that.
Hand mixing yields fewer bubbles and helps work out the normal bubbling caused by the concrete reaction. Mixing with a drill/mixer causes extreme bubbling. Using a mixing container with a lot of surface area (not a 5 gal bucket) also helps to disseminate bubbles. Home Depot has a great plastic pub 4ft x 2+1/2ft. that’s used in making plaster. It has rounded inside corners and is very easy to use.
6) Be careful about adding more liquid until the mix is wet with no dry ingredients on the bottom. That’s when the superplasticizer kicks in and you can easily make the mix too thin. It should be about the consistency of medium oatmeal or thick pancake batter. Best to err on the side of too dry rather than too wet. Use the rule of being able to hold the mix in 2 cupped hands without it running out.
7) Don’t use more CaCl than necessary. It will set faster, but it weakens the stone. With all the work we put into these things, you really don’t need to unmold it in 2 hours. I like mine sort of “green” because it’s easier to grout the invariable little pin holes they all have around the glass pieces or to remove any concrete that may have seeped under the contact paper. If it’s not well set it will develop cracks…bummer. Don’t unmold until you hear or feel a CLICK when the stone is tapped with a fingernail or metal object. If it THUMPS, let it sit for a few more hours.
I never use more than ONE cup of CaCl… EVER. Most of mine are unmolded in 8 to 12 hrs depending on the time of day they get poured and the temperature. I do them in a detached garage, but since we only have about 2 days of winter down here in the Gulf South, temperature wasn’t a problem.
If you color your mix (I put the dry pigment into the dry mix) remember to SAVE about a cup of it, before adding liquid, to use for grouting later. It will match the stone grout lines perfectly. Make your colors about 2 shades darker than you want them … stone colors fade as they cure and that takes up to 2 weeks before the color is stable. Test for a color intensity by putting a big pinch of the colored dry mix in a cup with a few drops of water. If it’s not dark enough, add more pigment and re-test. I usually wind up with 3 to 4 tablespoons of pure pigment in a 14″ stone.
9) Do yourself a favor and get a good mold release agent. Vaseline, Pam and WD40 are minimally useful. I use Crete-lease 20VOC. Get it from cresset.com. Maybe you can even find some locally … just be sure that the product won’t harm your vinyl molds. Along with being a superior concrete release agent, it will also help prevent the surface tension that holds tiny bubbles on the stone surface… we call them “bugholes”.
10) Pour concrete starting at the edges (helps hold down the adhesive paper). Cover the bottom with a thin layer and “wiggle” and pat gently to help fill the grout lines and release little bubbles.
Do this twice more … adding a layer and patting to get bubbles to rise. When you’ve finished screeding (leveling) and floating (smoothing the bottom surface with a trowel etc.) wipe all concrete off the mold edges. Tap the table gently all around the stone for about a minute or two. Be gentle, because if the bottom moves too much, concrete will run under the contact paper. You can tap the underside of the table, but that’s more perilous than side agitation. DO NOT tap the edges of the mold itself. Gotta get those bubbles out! You’ll still have a few little spaces around glass pieces, but they are so easily grouted with the dry mix you saved (just add acrylic).
Send me pictures of your Stones for the Stone Gallery. Take pride in your activity and your art. Use the Stone Forum for help and support and fun. It’s there for you.
Be sure to read the “Tips and Tricks” section, which is an addendum to the Manual and contains important information. Also, the “Other Manuals” section has more important info like the cost estimate and measuring the amount of mix for a mold.