The traditional base for a cobblestone patio is 4 to 6 of compacted gravel above the ground. If you're going to install a roadway or road intended for vehicle traffic, you'll need to double the thickness of the gravel layer. What depth of base materials is necessary? There is no absolute rule for determining the required depth, however, recommendations vary depending on use. The guidelines are 4 to 6 inches for pedestrian walkways and 8 to 12 inches for entrances.
Local soil conditions also affect depth requirements. In general, clay bases need to be dug deeper to facilitate drainage. If your pavers are located around a pool or are going to receive vehicle traffic, your subbase should be between six and eight inches thick. The additional thickness of more than six to eight inches can help reinforce pavers that will support extremely heavy vehicles, such as semi-trailers or motorhomes.
Some builders do not use this traditional anatomy, replacing the gravel layer with a plastic cobblestone panel. Some homebuilders say there's no need to use gravel under pavers and, for simple jobs, you can simply place them directly on the ground. However, the base of the cobblestone is not the aesthetically pleasing gravel used for the driveway or potted plants. Once you've decided on the depth of gravel you need, it's a simple calculation (depth multiplied by surface area) to decide how much gravel you need to order.
With a similar function in the context of placing a patio, you can use gravel as a base when laying paving stones. Your supplier may also call it “¾ less gravel” because it's usually the size of the largest pieces (in inches), but you can also get gravel larger than 1 ½ inch. Gravel is truly the ideal material for the base of the paver, since it is strong and durable, compresses to form a hard layer and, as we have already mentioned, is ideal for drainage. While the base of the cobblestone is thicker and closes more firmly than the gravel, both are used to form a thick layer on the landscape cloth that is then covered with sand on which the pavers are placed.
Like the thicker cobblestone base itself, gravel can be successfully used to create a thick layer on top of the landscape fabric, before placing the layer of sand and pavers on top. We'll look at the anatomy of the cobblestone base in more detail later, but these are the basic rules for gravel layers. Most experts suggest at least 4 inches for the gravel or crushed stone layer, and then an additional inch for the sand layer. The only significant difference between gravel and the base of the cobblestone is that the sharper edges of the base of the cobblestone mean that it can bond more effectively than gravel when it accumulates under sand and pavers.
We also suggest that you use coarse-grained gravel under pavers if it rains a lot where you live or if you have problems with runoff water.