Stonework can certainly be beautiful and can add value to your property. Unfortunately, it's not very easy to install. Most of the problems are in the material itself. Unlike consistent building units, like bricks or cast concrete pavers, natural stone comes in variable thicknesses. When you order nominal 25mm-thick stones, for example, you get pieces that have one flat side but that vary in thickness from as little as 15mm up to as much as 28mm. Because your goal is to create a finished surface that is as flat as possible, this means you have to custom fit the bottom of each stone in the sand base, which can be extremely time-consuming even after you get the hang of the job.
If you're laying a patio that is going to abut the house, plan to slope the installation away from the house so water can drain off. A 25mm drop for every 2.5 metres of run is a good minimum figure.
Proper base preparation is a matter of some debate. Most sources recommend at least a 100mm-thick layer of compacted gravel covered by a 50mm layer of compacted sand. If a patio were to be completely exposed to the weather, we would omit the sand and just use a 150mm-thick gravel base because it has better drainage.
On this job we used the sand layer because the patio was covered by an enclosed porch above, and because it made it much easier to fit the stones in place.
Begin site preparation by removing the sod in the patio area. Then spread gravel on the site using a shovel and rake.
Pull a screed across the gravel until the surface is flat. Add or remove gravel from areas as needed. Once the surface is flat, compact it with a plate compactor,available for hire stores. If you haven't used one of these machines before, it's a good idea to work in the centre area of the patio site first. These machines can be hard to control, so it's smart to get comfortable with your machine before you work close to the house.
Add a few centimetres of sand and spread it with a shovel and a rake. Then screed it to finished depth and flatness with another screed board, using guide boards to support the ends. Compact the sand with a plate compactor as you did with the gravel. Three passes should be enough.
Before you begin placing stones in the sand, you must establish a square corner. To do this take a long, straight board and place one end against the house where the patio corner will fall. From the corner point, measure over 1.85 metres along the house wall and make a mark. Then, measure 2.5 metres along the second wall and make another mark. Have someone hold the end of a tape measure at the house mark and adjust the board until the 2.5 metre mark intersects the 3 metre mark on the tape. Drive a stake at the end of the board and tie a string from the house corner to this stake. Tighten the string so there is enough space to slide a scrap wood block between it and a stone below. By aligning the edge of the end stones with this string, you'll ensure that your installation starts square.
With your square starter string in place, slide the corner stone into position. Check its height by sliding your scrap block between the string and the stone. Then check for level from side to side. To make the stone fit properly, lift it up and either add or remove sand from the base using a trowel.
Lay the next stone in your pattern. Maintain a joint of about 12mm between the stones, and check that the matching faces of the stones are flush and that the second stone is level with the first from side to side. As you add more stones, always make the edges meet flush and check the overall slope frequently, especially as you work farther from the house. A long board with a 1.2 metre level on top should serve well.
Once all the stones are laid, align the grout joints using a pry bar or flat bar. You'll have to make some compromises on this step because not all the joints will line up perfectly. Just favour the ones that will be more visible and let the others fall where they lie.
You can grout the joints with sand. Spread the material you choose over the patio and use a broom to fill the joints. Pack the sand into place with a mason's trowel. Some joints will take more material than others. When all the joints are full, sweep any of the excess off the patio, then rinse the surface with a gentle spray of water from a garden hose. Avoid spraying a strong stream right into the joints because this will flush out the packed sand.
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