A common misconception with paver patio construction is that the pavers are just laid on flat dirt or a bed of sand. Homeowners typically think the cost of a new patio is derived only from the cost of the paver product. Excavation and foundation prep are a huge component of paver patio construction and cost, and performing them properly is critical to your new hardscape’s longevity and ensuring it withstands the annual freeze and thaw cycles of Michigan soil.
When a new patio installation starts, the ground needs to be excavated to a depth of about 10 – 12 inches across the entire space where the finished patio will stand. This depth allows for enough crushed stone to be filled in and compacted for a strong foundation along with the thickness of the paver itself.
Before adding the base stone or foundation, the soil needs to be compacted first. The compaction is done with specialized compaction equipment. A heavy, woven geotextile fabric is then laid across the subsoil and wrapped up the sidewalls of the excavated cavity. The fabric is not meant to prevent weeds from growing up through the pavers; it acts as a barrier between the subsoil and crushed stone so that the soil does not migrate into the stone over time and cause settling. The fabric also stabilizes the base stone and is sometimes referred to as “rebar for dirt.” It is permeable, so it still allows for water movement between the soil and stone.
Once the fabric has been laid on the soil, clean crushed limestone is added to a depth of approximately 7 – 8 inches for patios or 12 inches for driveways. The crushed limestone base consists of angular stone pieces that are about ¾” in diameter. The jagged edges and absence of fine dust particles allow for maximum compaction, strength, and water movement through the stone base. In southwest Michigan, it’s critical that water is not held within the base of a paver patio. If water is not held in the base, the freeze and thaw cycles during the cold season will not cause expansion and contraction of the ground underneath the patio, and therefore will not affect the integrity of the pavers.
The larger ¾” crushed limestone is adequately compacted with a vibratory plate compactor until the proper depth is achieved. Long steel pipes, approximately 1” in diameter, are laid across the stone base and spaced 4’ to 8’ apart. The slope of the pipes is checked with an elevation measurement tool to ensure proper slope of the pavers above once the patio is finished. The top layer of the base is a 1” thick bedding of a smaller clean, crushed limestone, approximately ⅜” – ½” in diameter. The smaller clean limestone chips are added between the pipes, and a long, smooth bar is laid across the top of two steel pipes. The bar is carefully slid across the pipes, which creates a smooth bedding to lay the pavers on.
Although this process can sound overwhelming on paper, your contractor should absolutely outline this process in detail on your written estimate or contract for your project. Know exactly what you are paying for when hiring a company to install your new paver patio, and verify that the contractor is not trying to cut corners on the excavation, base depth, or type of base material. These construction principles apply to retaining walls, outdoor kitchens, fireplaces, and other hardscape structures, so make sure your project will be built to stand the test of time before you hand over your hard-earned money.