- Stepping Stone Mold
- Mold Release or Light Vegetable Oil and Paint Brush
- Plywood Base Boards
- Particle Mask + Rubber Gloves
- CHENG Outdoor Pro-Formula Admixture
- Sakrete 5000 Plus Concrete Mix
- Wheel Barrow or Bucket
- Mixing Shovel / Hoe / Trowel
- Plastic Drop Cloth / Plastic Bag
Caring for your Mold:
- To protect the mold, place it on a plywood base board to move it around during and after the pour. Lifting the mold from the plastic rim when it's filled with concrete will cause stress and eventually the plastic mold will develop cracks. (A well cared-for mold will last a minimum of 20+ castings).
- When it's time to de-mold, make a 'plywood sandwich' and flip the mold over using the wood, not the plastic rim.
- After the concrete is released, the leftover residue in the mold can be cleaned off with light soap and water.
Step 1: Prepare Mold
- Simply brush a little bit of light vegetable oil or mold release in the form.
- If the oil makes little puddles, you've used way too much. Soak up the excess with a paper towel.
- Too much mold release will make air bubbles in the surface.
- Not using mold release can make the stones more difficult to de-mold, and you'll need to be more careful about damaging the mold.
Step 2: Mix Concrete
Mixing can be done with a proper concrete mixer, in a wheel barrow with a concrete hoe, or by hand with a trowel in a 5-gallon bucket. If you're mixing by hand, it's really important to take your time and get everything completely mixed.
For tips on mixing concrete, check out the How-To-Mix Concrete Instructable.
- First mix the dry ingredients together (Outdoor Pro-Formula / Sacked Concrete Mix). Break up any big clumps or throw them out.
- If you're using Outdoor Pro-Formula, do not follow the directions on the sacked concrete. Since it contains a water reducer, this means you will use less water (for more strength) but the concrete will still be flow-able.
- Slowly start adding 1 gallon of water. Add about 2/3 of it.
- Mix a little bit and gradually add the last 1/3 gallon. The most common mistake is to wet the mix out too much.
- If the mix is still dry and gritty, add more water.
A simple method of checking the workability of the mix is to perform a slump test. The slump is the vertical distance the concrete settles.
- Poke a 1/4" hole in the bottom of a plastic cup with a pen.
- Fill the cup with the freshly mixed concrete and pack it in.
- Place the filled cup upside down on a flat, rigid surface.
- With your hands, carefully vibrate the cup in a steady lifting motion and lift it up without stopping.
- The ideal slump should be about half the height of a 15 oz. plastic cup.
Tip: In cold weather, use warm water to accelerate the set time. In hot weather, use cold water to slow the set.
Step 3: Fill Mold
- Fill bottom surface of mold with 1/2" of concrete and pat it down vigorously to drive out air bubbles.
- Lift one edge of the plywood base board and repeatedly tap / drop it up and down to help vibrate the first coat of concrete and draw more air bubbles to the surface. Repeat with all four edges, then fill mold to the top.
- Smooth the top surface with your hands so the concrete is flat and level.
- Finish by tapping and shaking the plywood base, driving out as many air bubbles as possible.
Step 4: Cure + De-Mold
- Place on a level tabletop.
- Cover with painter's plastic and wait 4 days to cure. The plastic covering the concrete will help keep the humidity inside, like a greenhouse, and this will minimize surface cracking. Ideally the concrete should cure between 50 and 90 degrees Fahrenheit, and it should never freeze while curing.
- After the stone has cured, place a plywood board on top to help flip it over without bending the rim of the mold. Then carefully ease off the plastic mold, pulling up gradually on all sides until it pops off.
Step 5: Finishing
- Sealing is easy and can help maintain the smooth finish the concrete gets from the mold.
- With a cloth apply a 50% dilution of sealer and water, agitate the surface for 5 minutes, then wipe away the excess and allow to dry.
- Check out the Sealing Concrete Countertops Instructable for more detailed information on the sealing process.
Grinding + Polishing:
- Grinding down to expose the rock aggregate will give the stepping stone more contrast.
- A water fed polisher is a highly useful, moderately-priced professional tool, essential if you're working with concrete on a regular basis.
- Dry polishers are also available and when hooked up to a HEPA vacuum, they eliminate the caustic dust that comes with grinding concrete.
Step 6: Placing Stepping Stones
- Stepping Stones are good for transitional spaces in the garden and for areas that get muddy.
- They can simply be placed on or planted into the ground for a snug fit.
- To plant into the ground, place the stone where you want it, and sprinkle flour along the border to mark the location. Dig a hole 3-4" deep and fill it with 2" of sand. Place the stepping stone in the hole and rock it back and forth until it's fully seated.