At the end of the day whether you are using concrete, asphalt, paving stone, or any other type of paving you are using it all is a covering of the real strength which is base. When we are basing for patios and sidewalks we aim for between 6-8 inches which is thirty percent more than is recommended by Interlocking Concrete Paver Institute, which recommends 4-6 inches and driveways we aim for 16-18 inches of base instead of 8-12. For our base we use three quarter inch limestone with down for the majority compacted in 2 lifts for walkways, and patios, and 4 lifts for driveways and we aim for at least 98 percent compaction. Then we use a finer quarter inch limestone at no more than an inch to perfect our level before laying our paving stone. We use this much base because we understand that our freeze and thaw cycles here in the great white north are harsher than where 4-6 inches of base may be adequate. We see this in the longevity of our projects. So far (fingers crossed) we have not had any warranty repairs that were due to shifting or sinking. The base really is what holds everything together so it is really important that not only does the finished product look good but what is underneath that product because what is underneath is what will mean the difference with an awesome product for years to come or a patio that has hills and valleys or driveway that is inches lower than your garage pad.