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Checks
- Each stone weighs about 54 lb; one bag of mix makes about 1.6 stones.
Shopping list
| Qty | Item | Est. |
|---|---|---|
| 2 | 2×3 stud, 8′ (board) | $7.20 |
| 6 | Concrete mix, 80 lb bag (0.6 cu ft) (bag) | $39.00 |
| 1 | Concrete form release spray (can) | $10.00 |
| 1 | Hardware cloth, 1/2″ grid, 24″ × 10′ roll (roll) | $18.00 |
| 1 | Plastic sheeting, 10′ × 25′ (for curing concrete) (roll) | $12.00 |
| 3 | All-purpose / paver sand, 0.5 cu ft bag (bag) | $18.00 |
| 1 | 2 1/2″ wood screws (box of 100) | $10.00 |
About $114 · rough estimates, check the store
Parts
| Part | Qty | Length | Width | Material | |
|---|---|---|---|---|---|
| A | Mold side Square ends. All four the same: they lap in a pinwheel. | 8 | 17 1/2″ | 2 1/2″ | 2×3 stud |
Cut list
2×3 stud, 96″ → A 17 1/2″ · A 17 1/2″ · A 17 1/2″ · A 17 1/2″ · A 17 1/2″
2×3 stud, 96″ → A 17 1/2″ · A 17 1/2″ · A 17 1/2″
Kerf 1/8″ included. Every cut runs edge to edge.
Steps
- Tape measure
- Speed square
- Pencil
- Drill/driver
- Clamps
- Safety glasses
- Hearing protection
- Dust mask
- Circular saw or miter saw
- Miter saw (30° cuts for hexagons)
- Wheelbarrow and a mortar hoe
- Magnesium float or a smooth wooden block
- Concrete edger or margin trowel
- Tin snips
- Flat spade
- Level
- Waterproof gloves and safety glasses
- Sander, 120 and 180 grit
1Before you start
Read every step once, start to finish, before you buy or cut anything. Each step names the parts it uses by letter; the parts list gives their sizes.
Set up somewhere flat with good light. A pair of sawhorses with a sheet of plywood on top makes a fine work table.
Wear safety glasses whenever a tool is running, hearing protection for saws, and a dust mask for sanding and for cutting treated wood or sheet goods. Tie back long hair and loose sleeves. Keep children and pets out of the work area.
- Tip At the store, pick straight boards: hold each one up to your eye and look down its length. Skip boards that bow, twist or have big knots near the ends.
- Tip Measure twice, cut once. Most mistakes are a misread tape, not a bad cut.
2Cut and label the parts
Cut every part on the cut list. Cut the longest parts first: if one goes wrong, it can still become a shorter part.
To mark a cut, hook your tape on the end of the board, make a small V with its point exactly at the measurement, and draw a square line through the point with a speed square. Put an X on the waste side.
Cut on the waste side of the line, so the blade's kerf (about 1/8″) comes out of the scrap, not your part.
Write each part's letter in pencil on a face that won't show, and stack the parts by letter.
Sand the faces before assembly while they're flat and easy to reach: 120 grit, then 180.
✓ Lay the parts out and count them against the parts list. Measure a few: if one is off by more than 1/16″, recut it now.
STOP. Let the saw reach full speed before it touches the wood, keep both hands clear of the blade's path, and never reach under a board you're cutting. Support long boards on both sides of the cut so the blade doesn't pinch.3Pick the pour day and line up help
Concrete is the one part of this job you can't pause. From the moment water hits a batch you have about 30–45 minutes to get it in place, then roughly 1–3 hours to finish the surface. Plan the casting for a day you can give to it completely.
Check the forecast. You want 50–80°F (10–27°C), no rain for at least 12 hours after you finish, and nothing below 40°F (5°C) for the next 2 days and nights. Rain on fresh concrete washes the paste off the top and leaves it pitted and weak; water that freezes inside it cracks it from within.
Hot (over 85°F), sunny or windy days make concrete stiffen about twice as fast. On those days start at first light, keep the bags in the shade, and mist the gravel or mold before you pour so it doesn't suck the water out of the mix.
6 bags of 80 lb mix is 480 lb. A car carries about 10 bags safely and a half-ton pickup about 20; past that, pay for delivery. Stack them on a pallet or boards off the ground and cover them: a bag that gets damp turns to rock.
You're making 8 stones with 2 molds: 2 a day, so 4 casting days. Each stone needs about 0.37 cu ft of concrete, so one 80 lb bag makes about 1.6 stones.
- Tip Lay everything out the evening before: bags, wheelbarrow, hoe, shovel, float, edger, a bucket of water for rinsing tools, a hose, and plastic sheeting in case of a surprise shower.
- Tip Concrete waits for no one, so don't start in the afternoon. A morning start leaves daylight for finishing.
✓ The forecast is dry for 12+ hours after the pour and above 40°F for 2 days. Every bag, tool and helper is on site before you open the first bag.
4Build the square molds
Each mold is four identical 2×3 sides (A), 17 1/2″ long, standing on edge so the stone comes out 2 1/2″ thick and 16″ square inside.
Lay them out in a pinwheel: each side's end butts against the face of the next one, going round in the same direction. That way every side is the same length and the inside is exactly square.
At each corner, drill two 1/8″ pilot holes through the face of one side into the end of the next, then drive 2 1/2″ screws: 8 per mold, 2 molds.
Sand or tape over any splinters on the inside faces: concrete copies every mark.
- Tip Drive the screws at one corner only part way. Backing those two screws out later is how you release the stone.
✓ Inside, each mold measures 16″ both ways and the two diagonals match within 1/8″. It sits flat on the floor without rocking.
5Oil the molds and set them up
Pick a flat, level spot out of direct sun: a garage floor, a patio, or a sheet of plywood on two sawhorses. Spread plastic sheeting over it.
Set the molds on the plastic. Check each with a level both ways; slip cardboard under the plastic to level one that tips.
Spray form release oil on the inside walls (and the bottom of plastic molds) until they look wet but not dripping. Wipe up any puddles.
Cut a square of hardware cloth 13″ × 13″ for each stone with tin snips.
✓ Every mold is level, oiled on every inside face, and has its piece of hardware cloth beside it.
STOP. Cut hardware cloth edges are sharp. Wear gloves.6Mix the concrete
You'll use 2 bags of 80 lb concrete mix for the 2 stones you cast each day. Mix one or two bags at a time in a wheelbarrow: concrete starts to stiffen in about 30–45 minutes (faster on a hot day), so only mix what you can place right away.
Pour about 2 quarts of clean water into the wheelbarrow first, then empty one bag on top. (Each 80 lb bag needs about 3 quarts in total.)
Mix with a hoe or square shovel: pull the dry powder from the corners and bottom into the wet middle and chop through it. Keep going until there are no dry pockets.
Add the last of the water a cup at a time, mixing between each.
Get the thickness right. It should look and feel like thick oatmeal or stiff peanut butter. A hoe dragged through leaves ridges that stand up, and a handful squeezed in a gloved hand holds its shape. Too dry: it crumbles and won't stick together, so add a little water. Too wet: it flows flat, water pools on top, and the concrete will be weak and crack. Then add some dry mix from a spare bag.
Mix one bag at a time: it fills about 1.6 molds. Over 4 casting days you'll use 6 bags in all. Fold a part-used bag shut, tape it, and keep it dry and off the ground for the next day.
- Tip More water makes concrete easier to push around and much weaker. Resist the urge.
- Tip Rinse the wheelbarrow, hoe and shovel before the concrete sets on them. Don't wash concrete into drains or onto the lawn: let leftovers harden in a scrap box and throw them out.
- Tip Buy one more bag than you need. Running out halfway through a pour is the most common mistake.
✓ Even grey colour throughout, no dry powder, no puddles of water on top; a ridge made with the hoe stands up.
STOP. Wet concrete is caustic and burns skin. Wear waterproof gloves, safety glasses, long sleeves and long pants. Open bags slowly and wear a dust mask: the dust has silica. Rinse any concrete off your skin right away.7Fill halfway and lay in the mesh
Shovel concrete into each mold to about half full, 1 1/4″ deep. Push it into the corners with a gloved hand or a trowel.
Tap the sides of the mold all round with a hammer (plastic molds: jiggle them) for 30 seconds. Air bubbles rise and the concrete settles flat.
Lay the hardware cloth on top and press it down lightly so it beds in. It keeps the stone in one piece if it ever cracks.
✓ The mesh lies flat, in the middle of the thickness, and doesn't touch the mold walls.
8Fill, screed and float
Fill the molds a little over the top. Tap the sides again for a full minute; you'll see bubbles pop on the surface.
Screed: drag a straight scrap of wood across the mold rim in a side-to-side sawing motion to strike the top flat at 2 1/2″.
Float the top with a magnesium float or a smooth block of wood in small circles until the stones disappear under smooth paste. Stop there.
Wait for the bleed water to come up and go away (20–60 minutes). When the thumbprint test leaves a dry 1/4″ print, float once more lightly. Now press in leaves, initials or a pattern if you like, and round the top edge with an edger or the tip of a trowel.
Finish with a damp stiff brush pulled once across each stone for grip.
- Tip Rough beats smooth outdoors: a glassy top is slippery when wet.
✓ Each top is flat and level with the rim, with no holes or exposed mesh, and the edges are rounded.
9Cover, wait, then take them out
Cover the molds with plastic so they don't dry out, and leave them alone for 24 hours (48 hours below 60°F). Don't cast if it will drop below 40°F overnight.
To demold, back out the two screws at one corner, spread the mold open and slide the stone out sideways onto a board. Screw the corner back together, re-oil, and cast the next one.
Stand the new stones on edge in the shade, cover them with plastic, and mist them every morning and evening for 7 days. They gain most of their strength in that week.
- Tip If a corner crumbles when you demold, the next ones need another 12–24 hours in the mold.
✓ The stones come out whole, with crisp corners and no crumbling. A fingernail can't scratch the face after a day.
10Set the stones in the lawn
After 7 days, lay the stones on the grass 24″ apart, centre to centre, and walk the line at your normal pace. Move any that don't land under your feet.
Cut round each stone with a flat spade, lift the stone off, and dig out the sod and soil 3 1/2″ deep.
Pour in 1″ of sand, level it, and tamp it with the end of a 2×4. Bed the stone on it and twist it a little.
Set each stone flush with the soil, or 1/2″ below the grass, so a mower passes over it. Stand on it and rock: add or scrape sand until it doesn't move.
- Tip Call 811 before digging if the path crosses the yard where lines might run; even shallow holes count.
✓ Every stone is level, flush or just below the lawn, and doesn't rock when you stand on one edge. You need about 3 bags of sand.
11Finish
Ease every sharp edge and corner with 120-grit sandpaper so nobody gets a splinter.
Sand all over with 180 grit, always along the grain (the direction the wood fibres run). Scratches across the grain show through stain.
Wipe off the dust with a barely damp rag and let it dry.
Paint, stain or a clear coat (water-based polyurethane is the easiest). Apply thin coats with the grain, let each dry fully, and sand lightly with 220 grit between coats.
Let it dry for the time on the can before using it.
- Tip Try your finish on a scrap of the same wood first: stain looks different on every board.
Conceptual layout, material estimate and assembly guide from the sizes you entered. Not engineering, not a building plan, not stamped or approved. Confirm measurements on site; follow local codes and product instructions; anchor tall pieces before use. Using this plan means you accept the Terms of Use.