Introduction: Concrete Chess Set for Outdoors
Chess is a social, quiet and contemplative game, perfect for a peaceful garden. But to be inviting, especially in a community garden, the set should stay outside year-round -- it should be made of concrete.
Step 1: Finding and Creating the Molds
I wanted this project to be easy and cheap. I didn't want a set which mimicked traditional carved wood, I wanted shapes proud to be made of concrete. The pieces should feel smooth and heavy, they should be fun to touch.
Ball pit balls make perfect pawn molds: the sphere is satisfying to grab, and it is relatively easy to get beautiful results. I found 100 ball pit balls for just $6.50 including shipping -- though when I just checked to link here the price has gone up and they're now $13.50. Oh well. Still reasonable though, when you consider the amount of fun you'll have with them...
Looking around the bottles at a deli I quickly found my king and queen: there is no shortage of feminine bottle shapes, but Pom makes a wonderful matronly queen. As for the king, when you turn many bottles upside down the bottom looks just like a crown. I chose "Sparkling Ice" because I liked the straight sides. The drink itself was not to my taste (though my teen liked it) but I did enjoy the 12 oz bottles of Pom (green tea & pomegranate pictured here, or a delicious coconut blend). It's a good thing too, because at close to $3/bottle the Queen was the most expensive piece.
My first thought for the rooks was a roll of toilet paper, but instead I used a plastic fluorescent tube cover I had lying around to avoid the interior marks of the cardboard tube. These required some preparation, which I will describe in step 3.
Since all these molds get destroyed after one use, you'll need to collect at least one per piece.
The trickiest pieces were the knight and bishops. I couldn't find any ready-made cheap molds which felt right, so instead I drew some 3D shapes to match the general esthetics of the set. Simple, geometric, and instantly recognizable as bishop and knight.
Step 2: Make the Bishop and Knight Mold
You can download the pattern to make these molds from my website (for free). They are formatted on US standard letter size paper, but you can print them on A4 as well.
I first tried making these molds with card stock. They looked great, as you can see in the first 2 pictures, and, after being wrapped in duck tape, they could hold the concrete -- however the weight and moisture of the concrete distorted the mold which became a bit more rounded than I wanted. It was too fragile for me to really bang around to get rid of the bubbles, and even though the tabs were on the outside, the wet paper became soft, and the tabs became plainly visible in the final cast. Building a support structure with legos didn't help either, so instead I made the final mold with a sheet of styrene.
Styrene is great: it's relatively cheap, you can print on it (though I didn't test that), it's easy to cut with an X-acto knife, and it held its shape beautifully for this application. After the first pour I was even able to clean up the mold and reuse it for the black pieces. Styrene's big problem is that it does not fold -- it just breaks. So when I prepared my molds I cut all the way through the styrene on the cut lines, then very gently, I cut only part way through the fold lines (on the mountain fold lines). While I slowly bent the sides I reinforced the folds with some packaging tape to keep them from breaking off. I also avoided folding any more than a 90° angle -- that way I was able to keep the molds together and perfectly aligned.
When the time came to take off the mold I just cut the tape along a few key edges and gently peeled the styrene shell open like a shrimp.
Note for laser cutter contest: a laser cutter really would have come in handy for this step, allowing me to make completely rigid, reusable molds...
Step 3: Prepare the Other Molds
I used the plastic cover of a fluorescent tube for the rooks, but toilet paper rolls would work just as well. You'll see the the mark from the roll, and the texture on the concrete's surface won't be so glossy, but if you attach a bottom and cover the whole thing with duck tape it should work just as well. Whether you are using paper or plastic, use plenty of tape to attach the bottom, you want the mold to be as watertight as possible. Even though it will hold your concrete, if water leaks out after you pour you will get little weak spots with a less attractive finish (see final picture).
Prepare the king mold by cutting off the top of your bottle. You will use the bottom part to fashion the king. Since you'll want to fill your mold to the rim, cut a straight line around the bottle at your desired height for the king. My trick for doing this is to hold a pen at the correct height (using some sort of prop to hold it steady) then, on a flat surface, to turn the bottle all the way around -- then cut it along the line with a box cutter or a pair of sharp scissors.
A 12oz bottle of Pom juice makes a great queen; she's a little on the buxom, heavy side, but the bottle neck looks particularly crown-like, especially with the addition of a marble. To prepare the queen you just need to saw off the very top, right above the "crown" and below the screw cap area.
Ball pit balls are very easy to cut; just make a small hole on one end, large enough to spoon in your concrete. Also keep an egg carton on hand to hold the balls after they've been filled with concrete. The plastic balls are very thin, so they wont hold their round shape if you put them on a flat surface to cure. You want the bottom (which will become the top) to be nice and round. Every little dent will show.
Step 4: Mixing and Pouring the First Batch of Concrete
The hardest part of this project for me was carrying that horrible 80 lb bag of pre-mixed concrete. You don't need anywhere that much for this project, but I wanted concrete for other experiments and projects too so I went whole hog. Big mistake. That thing's a bear to carry.
The second hardest thing was using and keeping my gloves on for the relatively fine work needed to fill these small molds -- but you REALLY need to use gloves, and if you're working inside, you REALLY need to wear a mask as well. Portland cement, the key ingredient of all forms of concrete (including stucco and grout) can be ground so fine that it can pass through a sieve which holds water... Mixed with water it turns hard as stone, plus it is so alkaline that it can burn your skin. Even minor contact will make your skin feel itchy and dry.
Stop a moment and imagine what happens inside your lungs when you breathe in that fine cloud of cement dust... then wear protection.
Besides that, mixing concrete is very easy and enjoyable. Get a pre-mixed bag so you don't need to worry about getting the right proportions of portland cement and aggregates (sand and small gravel). Add just enough cold water so that all the cement is completely wet... then add a tiny bit more water to make the texture less clumpy and easier to pour. It will be harder to get all the bubbles out of a drier mix, but you don't want it to be too wet and runny either. Don't worry too much about getting it just exactly, precisely wet. You're not building a bridge, and mixes with varying degrees of moisture will give good results.
Start with the white (i.e. plain cement) chess pieces. Get all your molds ready before mixing the concrete: the knights will need something to hold them up (I used plastic cups) and just to be safe I also supported the bishops. Mix the concrete in you bucket between each piece -- this will help prevent it from hardening before you're done, especially if you got a quick curing cement mix. As you're filling the mold shake it and gently bang it around to get rid of bubbles and to make sure the mold is completely filled. Even with clear bottles it's hard to see, so bang, shake and jiggle away. Once the mold is full to the brim, flatten the top with your trowel and lay it on a flat, level surface to dry. Unfortunately the table I was working on was NOT level, which is why my rooks look like miniature towers of Pisa -- nothing a grinder can't fix, but it's much easier if you get it right from the start.
I decided I wanted my queen to have an extra jewel on her crown -- so after filling her up (more like stuffing her, actually, to be sure all those curves would be smooth and round) I topped her with a white marble. Don't worry if the marble gets dirty, that will come off. Just push it down firmly. When you bang the Queen a little after that to get rid of the final bubbles, the marble will sink to its final position. Don't touch it or your other pieces for at least 24 hours.
Step 5: Curing
The third most difficult thing about pouring concrete is waiting for it to cure. Even fast setting mixes still take weeks to fully cure and reach their optimum strength. It is best to leave the pieces in their molds for as long as you can contain your curiosity or else bad things can happen. You piece might be set and hard to the touch after a few hours, but at this point it is still very fragile, it can crumble easily if you take off the mold. Also cement needs moisture to cure, so keeping the pieces inside your molds will prevent evaporation: it will cure faster and end up stronger. If you really can't help yourself, or if you want to re-use the bishop and knight molds to pour your black set, wait at least 24 hours, then be very careful and gentle. After you've removed the mold (don't tug, instead cut off the tape and gently peel it off) place the piece in a plastic bag, maybe add a moist paper towel (but don't let it touch the piece directly) tie a knot and leave it alone.
The pawns, being round, aren't as fragile as the bishop and knight, so they're safer to handle after 24 hours, but don't even THINK of touching the queen for at least 48 hours, longer if you can stand the wait. The problem with her isn't so much her shape, which is fairly solid, it's the fact that Pom bottles are much thicker and stronger than all the other molds I used. I didn't wait long enough to take off the black queen's plastic dress, and in the process of struggling with a knife, razor blade and pliers she got badly chipped. It wasn't all bad, because I got to treat myself to the coconut Pom drink, but it's better to wait and avoiding damaging your pieces. They'll be strong soon enough.
Step 6: The Dark Side
You have two alternatives for your black chess pieces: you can either buy a special pigment to mix into your concrete, or you can ignore what I said in my last step about waiting patiently for your pieces to cure and create instead a "pebbly" set.
If you take your pieces out of their molds after they have set but before they have fully cured (with the cement mix I used, that meant 24 hours after pouring), you can rub them gently under running water to scrub off the smooth cement surface to reveal the aggregate below. The opposing sides won't be black and white, just two subtle shades of grey textures, which can be a nice option if it corresponds to your worldview. It also has the advantage of smoothing over some defects (specifically bubbles) though it won't completely hide unwanted bumps. Still, it looks kind of cool and ancient.
If you opt for the pigment, buy the stuff specifically designed for cement at a hardware store and follow the directions on the box. The pigment should be mixed first with your water, which will distribute it evenly.
Keep in mind that concrete tends to become lighter over time -- but this goes for the plain concrete as well as the colored mix -- so even though these pieces won't look quite as glossy black and beautiful as they did fresh out of the mold, your black set will still be easy to differentiate from the plain concrete.
Step 7: Finishing
After they have cured you can grind and buff the pieces to your heart's content. You can also seal them, which gives them a smoother finish and will prevent marks if one of the chess players has greasy fingers.
Floor wax will work perfectly but you will need to buff it after applying the wax -- it's more work, but when you touch the piece it still feels like concrete, which is nice, as opposed to a coat of acrylic paint, which is easier to apply, but less satisfying from a tactile point of view.
Most cement sealers I found at the hardware store came in huge quantities designed for sealing the floors of a warehouse -- but then I found Weldbond, a universal adhesive. When you dilute one part Weldbond with 5 parts water it can be painted on concrete to seal it. It doesn't smell bad, it's easy to use, it will penetrate rough irregular surfaces, and the results were great even though I applied it before the cement was fully cured. It's a good solution if, like me, you're too lazy and impatient to wax and buff.
Besides the test pawn in this photo none of the pieces photographed here have been buffed or finished. I'm going to let them sit through the winter and polish them up before I put them out for everyone in the Spring.
I hope these will inspire you to make your own set (please post an "I made it" comment with a picture!). I will give a 3 month pro membership to the first person to post an "I made it" photo!
If you'd like to see some of my other work check out my website.