Choose a mix that doesn't contain gravel (also called aggregate) and follow manufacturer's instructions. We chose Sand Mix, which is a combination of cement and sand, for a smooth finish. The bag will tell you how much area the contents will cover, how thick a coating is recommended (Sand Mix is for areas requiring less than two inches, or five centimetres, of coverage) and how to mix it.
Large plastic tub
Long stick (for mixing)
Flat piece of wood (for
levelling wet concrete)
Acrylic bonding agent
You'll have to make these yourself, but the process is quite simple. We used medium density fibreboard (MDF) because of its straight edges and flat surface. Another option is melamine, but this is a bit more expensive. Bits of wood leftover from other projects are cheapest, but make sure all the pieces are straight. If you don't own a saw, just go to a building supply store that has a cutting service. Usually, the first few cuts are free for material you are purchasing, with a nominal charge for additional cuts. (Work out the dimensions for your moulds in advance, as dithering over the details won't endear you to the employees, as we discovered.)
First establish how many moulds you need based on the amount of concrete you are mixing. We went for moulds 12" square and 1 1/2" high, using 1/2"-thick MDF. One mould required a 13"-square base, two 13"-long, 1 1/2"-wide side panels and two 12"-long, 1 1/2"-wide side panels. Corner brackets (also called L-brackets) hold the side panels together or, if you have thicker side panels, you can screw them directly into the base.
DESIGNING THE PATTERN
Rub vegetable oil on the insides of the side panels and base so the paver doesn't stick to the mould. Now you're ready to create your pebble designs. We used polished river rock, but any combination of pebbles, shells or marbles will work; just make sure they're only half as thick as your mould or the concrete won't be able to hold them.
Pour a handful of sand into the mould, then spread it out. A layer about 1/4" thick should suffice. This keeps the design in place when you pour the concrete and allows for a slightly raised pattern. Arrange the pebbles in the design of your choice.