Last Revised 06/21/2004
These instructions are basic and even though they refer to the ingredients formulated by Cole Sonafrank, they are valid for any kind of concrete fabrication. They are designed to produce a better, less expensive and stronger stone than the commercial, studio powdered mixes.
In the Glass arts there’s only one sure thing and it’s that there are dozens of different ways of accomplishing the same result. True, some are easier and some are better, but you’ll hardly ever get 2 glass artists to agree. It’s a very lively scene. I can give some of the lessons I’ve learned in developing the techniques I use. They are not, by any means, the only ones, but if they work for you they’re the best.
1) Full-sized patterns are sold by all suppliers or you can make your own. A pattern can be made from anything. If you’re not good at “cutting” lines in a regular picture, stick to the stained glass and Stepping Stone patterns (there are thousands of them on the internet if you know where to look). A benefit of real Stone patterns is that they come mounted in a circle or Hex form. You can do that too with any stained glass pattern.
2) Sizing patterns is easiest if you have a scanner and a resizer program. I use a simple program that I bought on the internet called the “Rapid Resizer” from sgdesigns.com. There are other, more sophisticated and more expensive utilities that take a bit of computer savvy, but if you have a computer and scanner do get one of them. The Rapid Resizer only does one thing. It makes patterns smaller or bigger and saves them in that form. I usually shrink or enlarge mine to an 8X8 inch picture. Off-line I put an 8″ circle around it. It’s not a necessary move, but I like my enlargements to look exactly like the stone). This is the raw material from which the Rapid Resizer scans and enlarges it to any size you want. It prints out as many pages as it takes to get your final pattern by tiling. Tape the pages together and you’re in business. The 8X8 picture can be scanned to a file, resized and saved. It can be retrieved by the Resizer program any time, but is also saved in the enlarged form in the RR.
Need another copy? Just print it out. Copies match exactly.
When resizing, take into account the 1/2 inch border allowance and make the enlarged copy at least 1 to 1+1/2 inch smaller than the stone mold size (accounting for the fact that ½” all around the edge will be 1″ smaller than the total pattern size).
If you’re not doing computer enlarging, use any method you feel comfortable with…Light box tracing etc. I really am a spaz when it comes to tracing and don’t want to do it more than once for a pattern.
It’s VERY IMPORTANT that you have templates of the molds. Adhesive backed paper must be cut exactly to the inside size of the mold or it will wrinkle at the edges allowing concrete to seep underneath. It will also transfer the wrinkles and lines to the stone surface or edges. You won’t want to pay attention to this detail every time you do a stone.
Using poster board, trace the outside of the mold bottom. Cut it out, just to the INSIDE of that traced line. Fit it inside the mold and trim if it’s still a bit large. Use it and save it for next time. I always mark the 1/2″ edge allowance on the template to be sure the pattern fits inside of that.
An ALTERNATE method of using adhesive paper for patterns that do not cover the entire surface of the stone is to cut the paper to fit ONLY the area where the pattern lies. Some people use this with success. I can’t recommend it because I haven’t used it, so it’s your choice. Remember, this is NOT for full-surfaced patterns that cover the whole stone.
ADHESIVE BACKED PAPER
1) Use a CLEAR adhesive paper. Some years ago, the “Contact” brand paper found in stores was fine for this purpose. Unfortunately, it has been re-formatted into an “acid free” product that tends to leave a heavy residue of the adhesive on the surface of the stone when it’s unmolded. This is undoubtedly a result of the heat of the concrete reaction dissolving the new glue formula. This residue is VERY difficult to remove. I suggest that you totally avoid the “Contact” brand of paper and find another product of the same type by a different manufacturer. Some of the Hobby stores and Hobby Lobby carry other brands. First, avoid any that state “acid free”. Some Stoners are using the “Clear Cover” or “Magic Cover” by the Kittrich Corp. You will need to search online or in your local stores for this one or a good form of adhesive-backed paper.
There is a very expensive form of adhesive backed paper sold by glass suppliers called “Mosaic Mount Tape“. Most adhesive paper comes in 18″ x 108′ rolls. Mosaic Mount is 20” X 10′ making it much more expensive. Many adhesives are 3.3 to 4.1 ml thick. MM is 4.5 ml. Did I try it? You bet I did and if it had been significantly better than ordinary adhesives, I would have paid the price gladly. Fact is, it’s not really better and may be worse in some respects. The ONLY time I have ever had seepage under the adhesive paper was when I used the high priced stuff. It’s possible that the heavier paper didn’t hold the glass as closely. Maybe it just didn’t adhere to the mold release in the bottom. It DID resist wrinkling on the edges better, because it doesn’t stretch as easily.
2) Now to the important part of adhesive film use. You MUST keep your roll of film from being flattened, crimped or wrinkled. Any lines or wrinkles it has will be transferred to the stone. I re-wrap my paper around a 2″ piece of PVC pipe but anything that won’t compress will work. The soft roll in the center of the paper is not enough to protect it. If you wind up with a few lines or creases in your roll, throw it away. It’s cheaper to buy another one and considering the price of the glass and ingredients in a good stone, the cost is insignificant.
3) Trace the template on the paper side of the con-tact and cut it out on the line. Check to be sure it fits EXACTLY inside the mold. You might get away with about a 1/8″ gap between the edges and the mold wall, but more than that is going to show in the finished product.
Make a REVERSE PATTERN: There are several ways to do this. The easiest way is to scan or import your pattern into a program like PaintShop or PhotoShop or GlassEye that will allow you to “flip” it or make a mirror image. I do this with an 8×8″ form of my pattern, then re-size the reverse image using those same programs or by scanning it into the Rapid Resizer and doing it there where I can store the original AND the reverse images to the same exact sizes. You can now lay this underneath the adhesive film while you fit the pieces. Remove it when you take the film out of the mold after all pieces are set.
A more “hands on” method is to put the un-separated, cut film on your light box or whatever you use to trace things (a window etc.) and, (here it comes, the part I hate most), TRACE your final, working pattern on theSMOOTH FILM side of the still unseparated paper (be sure to also trace a line for the 1/2″ allowance edge). Now, when you separate it, you’ll have a reverse pattern (more on that later). Just put it aside for now.
1) Place the base pattern copy on the template to be sure it fits INSIDE of the 1/2″ edge allowance. Now, position the base pattern on the workbench as you do for any glass construction. It’s a good idea to block it off with Morton layout blocks or at least put pins around the outer pieces. This can be built on homasote or ceiling tile. It will be a BIG, freeform construct and will shift around a lot. Know where your edge limits fall. Some patterns deliberately have a few pieces that intrude into the 1/2″ margin and that’s OK, but if your glass runs to the very edge of the stone, it’s likely that some of it will not be surrounded by concrete, and that’s UUUUGLY!
2) Use a Mosaic shears (just like the foil shears, but gives a 1/8″ gap) to cut out the pattern pieces. It will totally EAT the small, delicate pieces, so you might need to use a regular scissors and cut those out on either side of the pattern line. You’ll get the hang of making that 1/8″ gap by the seat of your pants. If it’s not big enough, grinding will adjust it. Lead shears might work, but they don’t produce 1/8″. Cut your glass as usual, (glad I don’t need to get into THAT kettle of fish), being sure that you’re using bright, opalescent colors. Cathedral glass appears dark and dull in stones and shows the concrete underneath. There is a reflective tape designed for use on the back of transparent glass. I don’t use it because I don’t like to put anything between the glass and concrete.
3) Fit the glass to the base pattern, grinding to smooth edges and adjust. Make sure there is a gap between all pieces and NONE of them are touching in any way. Un-ground pieces may have irregular, rough edges that are very obvious in concrete.
I usually begin the fitting by doing the outside pieces…being sure they fall to the inside edge of the 1/2″ allowance margin line or, if your base is pattern only, (without the extra paper making up the margin), that they sit on the very edge line. If you’re not doing a full-surface glass pattern and want the concrete to form a background, just fit your glass to the pattern.
You’ll notice that a lot of ‘nude’ backgrounds have mosaic borders of some kind, or scrolls. The logic here is that they will help hold down the edges of the film and prevent seepage.
Any mosaic border should start with the outside edge ON the 1/2″ border line. These also give a more finished look. It’s easy to do as well.
Don’t underestimate the shock of leaving that big 1/8″ gap in glass. We’re all trained to fit close.
MOLD PLACEMENT … OR, UPSY DAISY
1) The base pattern is done. Now, separate the adhesive paper and lay the film in the mold STICKY SIDE UP (if you’ve made an image reverse pattern on a separate paper pattern, put it under the contact paper in the bottom of the mold). You are now looking at an upside-down pattern. Since you will want the good side of the glass to be UP when the stone is unmolded, it needs to be placed FACE DOWN on the sticky side reverse pattern.
I do this inside of the mold but some people do it on the benchtop and some just try…and I do mean TRY… to cover the base pattern with the sticky film. It’s kind of like coughing and burping at the same time.
2) Transfer the pieces to the film pattern…good side DOWN. I’m not going to tell you that this isn’t tricky, but it works. Try to place them exactly as they were on the base pattern. You can get away with lifting and repositioning if you’re careful and IF the edges don’t stretch and get wavy or wrinkled. Don’t press down on the glass until you’re finished with the transfer.
3) Press down on each piece of glass. Tip the mold and GENTLY slide the Film/glass out onto the workbench (if you’re using a reverse image paper pattern for placement… remove it now). Use a rubber float or a wide piece of wood to push (or use a rubber hammer and tap) the glass down firmly… but GENTLY.
4) Spray the mold sides and bottom with a good CONCRETE MOLD RELEASE. I use “Crete-Lease” from cresset.com. Maybe you can find this locally. Pam and WD-40 do nothing for the smoothness of the surface and don’t inhibit the little pinholes (called bugholes) that are formed by tiny bubbles. After spraying, spread the release evenly in the mold using a paintbrush or paper towel. Be sure all surfaces are coated evenly but do not allow it to “POOL” in the bottom. If you spray the mold before transferring the glass, some of it will get on the film, destroying the adhesive properties. DON’T use Vaseline. It leaves lines and marks in the stone even if you heat it first and brush it on. If you want to simply lift off your mold after inverting, instead of fighting it get a mold release product.
5) Tip the lubricated mold so that the edge meets the benchtop. Gently slide the film/glass back into the mold. The lubricant will allow you to move it around a bit into perfect position.
Push down on each piece of glass again to assure it’s well seated. Check that the edges of the con-tact film are lying flat on the bottom of the mold and not climbing up the sides.
POURING A STONE
1) Mix all the dry ingredients (cement, sand, fumed silica, fibers ) together in whatever you like to use. I like my big plaster-mixing tub from Home Depot. Some people use a 5 gal bucket. I can’t get all the dry stuff off the bottom in a bucket. Also, the more surface area in the mixing container, the better air/bubble release you get during mixing. Mechanical mixers on a drill make BUBBLES! and those are the enemy. Double-glove with latex gloves and mix by hand.
2) Add the dry colorant to the dry mix (I prefer dry pigments and these instructions are for those, but liquid can be used in a wet mix). Start with a couple of tablespoons….mix in thoroughly. Test it for color by adding a bit of mix and some liquid in a cup or bowl that has a light colored bottom. Remember that concrete fades during curing. Make your color about 2 shades darker than you want it to finally be. Once you have the desired shade, save about 1/2 to 1 cup of the dry mix in a sealed plastic container to be used for grouting. All stones will wind up with a few spaces next to glass pieces. These are easily grouted after unmolding, using your “perfect match” saved mix.
3) Mix the dissolved (in 1 C water), cooled, Calcium Chloride and dissolved Superplasticizer with some of the Acrylic liquid (about 2 cups). Refer to the formula ingredients in Part 2 for handling of these additivesor to the “TIPS and TRICKS” method addendum for making a batch. Add to the dry ingredients and mix with your hands or a hoe or anything that moves the stuff. I just double glove with thin latex gloves because I like to feel as I mix and big, chunky kitchen gloves don’t let me do that. WEAR A MASK when working with dry cement and fumed silica. Just a painter’s mask will do. Superplasticizer should be dissolved (refer to the TIPS and TRICKS section for batch-dissolution of Superplasticizer). You need to agitate it constantly or it makes a nasty plastic glob. I use an old kitchen mixer, but a paint stirrer on a drill would do as well or better. You can mix it with some acrylic… separately from the CaCl before adding to the dry mix, or add the 2C acrylic, CaCl and Superplasticizer together before pouring into the dry mix. Keep adding acrylic a little at a time until all the dry mix is wet.
CAUTION… it takes the Superplasticizer a few minutes before it “kicks in”. Remember that it’s a water-reducing agent and if you add the Acrylic too fast, before the ‘Splazer’ reacts, you can wind up with a mix that is too thin.
The rule for mixing is to do it for at least 5 minutes. I KNOW it takes me a lot longer than that to get the right feel… maybe 5-10 min, by which time, I’m practically inside that darn tub. Final consistency should be like THICK Pancake batter or medium oatmeal. Brownie dough concrete is too thick … it’s what they use with chicken wire (buk, buk). You should be able to hold the mix in 2 cupped hands without it running out. Each Artist has his/her own gauge for consistency. In the end it’s a matter of experience.
Allow your mix to rest for about 5 minutes before pouring. This allows bubbles to rise and escape. It sometimes helps to lightly bump the mixing container during the rest period. Be Gentle. Vigorous bumping can cause more bubbles than it releases.
1) Start adding concrete at the EDGES of the mold. This helps hold down the adhesive paper. Place a thin layer to cover the bottom. Pat and wiggle between the glass pieces with your hands to help it flow into the grout spaces. Pat … pat … pat the surface to make bubbles rise. Do this gently so you don’t disturb any of the glass pieces. Add another layer and pat the surface to make more bubbles rise. Do it once more after the mold is full, or as full as you want. It’s OK to slightly under-fill the mold to the 1 +1/4″ mark instead of the 1 + 1/2″. This avoids the little flaring “lips” that sometimes form on the stone edges. However, a thinner stone is a weaker stone. Wiping the mold rim also helps avoid “lips” (see the discussion of Lips in the Tips and Tricks addendum).
2) Screed the surface (scrape off the excess with a piece of wood…or whatever will span the whole mold bottom). Float the surface (smooth it out with a wooden or rubber float, a trowel … or anything that works). Wipe the edge of the mold until it’s free of concrete. Tap the surface of the bench on the sides of the mold with a hammer or trowel, (or whatever is handy where you work) for a minute or so. This gets out the small bubbles that are still trapped even after all that patting. Don’t over-do it or you’ll disturb the glass. Tapping the bottom of the bench is more likely to disturb the glass, but it’s a technique that many “stoners” use. DO NOT tap the edges of the mold. This makes more bubbles than it releases.
3) Be sure your mold is sitting on something level (I actually use a carpenter’s level on the benchtop to check it). This concrete mix is not self-leveling. You will need to distribute it evenly in the mold. That’s easier when it’s filled to the full 1 +1/2″.
4) DO NOT MOVE the mold during the set time. It will develop little cracks all around the edges. Let it sit until it makes a CLICKING sound when tapped with a fingernail or metallic object. If it THUMPS, wait. Time is not the issue here. We balance the amount of CaCl (which weakens a stone in high concentration) with the water reducing properties (which strengthen a stone), but set time extension of Superplasticizer to obtain a successful set time. Most stones made using CaCL set within 8 to 12 hours. It’s affected by temperature (colder = slower) and humidity (high = slower). Don’t risk a stone by being too impatient. Clocks have no place in making good Stepping Stones.
WE do like to get the stones unmolded when they are still “green” and that means well set, but still soft enough to allow for easy surface cleaning and grouting. I wouldn’t leave a stone in the mold for much longer than necessary and certainly not more than 12-18 hrs under ordinary circumstances.
1) Invert the mold onto wooden dowels that span the whole surface size. If you’re using Mold Release you’ll be able to just lift the mold off the stone. With other lubricants, you may need to work your hands around the edges to loosen. Hot towels on the bottom help….or a hair dryer. They make the plastic mold more flexible. Only time I had to use that trick was when I forgot to lubricate the mold… duh… (also see the Tips and Tricks addendum for removal hints). If you use a rigid mold like a stainless pan instead of a soft ABS plastic mold, expect to have some trouble unmolding it. Lack of flexibility is a problem with concrete molding.
2) Remove the adhesive film. Take a good look at your stone. It’s possible to have a thin, filmy remnant of concrete on the glass…just wipe or scrape it off. Look for those little gaps around the glass. Mix a bit of your SAVED, colored, dry ingredients with acrylic or water, (you might want to sift it to get the nylon fibers out first). Rub the grout into the holes. Let it sit about 10 min and wipe away the excess. There should be NO glass edges protruding above the surface…or buried below it and no lines or transferred marks on the edges. This is especially important when the background is not all glass, but is formed by the concrete itself.
3) DO NOT MOVE the stone for at least a week. Even after that, be gentle with it until close to the finished cure time (30 days). Keep it elevated off the floor or benchtop on the dowels to allow evaporation from all surfaces as it cures. Too fast drying and curing weakens a stone. If you cure your stones in a very HOT environment or live in an excessively dry climate, it helps to keep them damp with a canvas or cloth cover that you spray regularly with water. There are actually some methods that call for curing stones underwater. I haven’t tried that one.
I can tell you that a stone made with the full set of Sonafrank ingredients becomes strong very early and can be moved or transported earlier than regular concrete stones. I have sealed some at 2 weeks and given them away to family with instructions that they keep it indoors for another 2 weeks and seal the bottom at 30 days. Had no problems yet.
4) I usually seal my stone top and sides after 2 to 4 weeks, but don’t do the bottoms until the 30 days have passed. Many concrete sealants will cloud glass. Do some tests before you use any of them. I use “Sealer’s Choice” from Home Depot. The best stone sealers are water-based TILE sealants. They come in many brands in the home improvement and tile supplier stores. Thompson’s concrete sealant is NOT acceptable as it will cloud the glass.
5) Apply sealant with a small paintbrush to the sides and GROUT LINES ONLY. Wipe off the glass while still wet. Let dry and repeat.
STONES IN THE GARDEN
Don’t be upset if the people to whom you give or sell your stones refuse to put them outdoors or in a place where they will be walked on or damaged by lawnmowers etc. My friends and family refuse to put them outside unless they are made into tabletops or placed in an out of the way area used for decoration. Some of the 12″ and 14″ stones are being used as kitchen counter trivets. Others are tabletops, sunroom decorations and goodness only knows what else.
If stones are put in the ground they must have a 1/2″ to 1″ bed of sand. Remember also that glass topped stones, especially if they are full surfaced patterns, can be VERY slippery when wet. They really are not the best type to use as a garden path stone. Mostly what I hear is that they’re “too beautiful” to walk on. OK. Just as long as they give pleasure to people.