EP Henry Paver Installation: Excavation and Base Preparation (part 1 of 3)
Congratulations on deciding to expand your outdoor living by installing a new patio (or walkway or driveway) using concrete pavers. Installing your own patio can be a very rewarding project, but before you start, it’s important to understand the key steps in a successful installation. At Penn Stone, we love helping do-it-yourself customers plan their project, but we also have seen plenty of customers who realize too late that they’ve gotten in over their heads, and this is often reflected in the finished project.
This post is the first in a series on successfully installing your new patio. I’ll break this down into three segments: excavation and base preparation; setting bed and paver installation, and finishing touches including installation of edge restraints and joint sand.
I often tell people that paver installation is a lot like painting – the time and care you take with preparation will define the appearance and performance of the finished product. And as with painting, preparation is the most time-consuming and monotonous part of the project.
First, it’s important to understand the scope of your excavation and base preparation. For typical patios and walkways, we recommend a 6” thick base of 2A modified stone (for paver driveways, more stone will be required). In order to accommodate the stone base, sand setting bed and paving stones, you will need to excavate until you are 9” below the finished height of your new patio. Before you start, be sure to think about where you plan to go with the soil you remove – 9” worth of dirt can create a very large pile - and you need to have a new home for this. You should decide in advance if you can place it somewhere on your property or if you need to haul it away.
When excavating, it’s also important to remove any soil you disturb. Soil compacts slowly and unpredictably over time. If you disturb soil, but tamp it back into place instead of removing it, you’re likely to see uneven settlement at that spot over time. If you dig too deep, it’s better to replace that additional depth with stone than with disturbed soil. After you’re done excavating, run a vibrating plate compactor over the unexcavated soil. This is a heavy piece of equipment, roughly the size of a walk-behind lawnmower, and can be rented from most local equipment-rental businesses.
After you excavate, the next step is to install a layer of geotextile fabric. This fabric serves to separate the soil from the stone you’ll install in the next step. It’s inexpensive, and can provide ‘insurance’ against uneven settlement. This fabric should be installed on top of the excavated area and should wrap up all sides of the excavation.
After installing the soil-separation fabric, you’re ready to begin placing the 2A modified stone. As you install the stone, you’ll need to compact it with a vibrating plate compactor to compact the stone to an appropriate density to prevent future settling after your patio is complete.
It’s important to note that typical rental compactors can only effectively compact 2” of stone at a time. Many homeowners have asked us to dump their entire stone delivery right into the excavated area. Unfortunately, this is not a good idea! If you spread all 6” of stone out at once, then run the compactor over the base, you’ll have a nicely compacted layer at the top, with 4” of poorly compacted stone underneath. Over time, this will result in a patio with many high and low spots.
Instead, you must compact your stone in 2” ‘lifts’. This means you will install 2” of stone, compact it, install another 2” of stone, compact that, and install the final 2” of stone and compact it. This is the only way to ensure that your base is properly prepared to produce a patio that will be flat and even for many years. During compaction, make sure the stone is damp without getting it overly wet. This will allow the stone to compact more easily.
Finally, as you are installing and compacting the last 2” of stone, it’s important to understand that how you carefully you level and finish this surface will determine the appearance of the finished patio. It’s critical that you make this as smooth and even as you want the finished patio to be. Some homeowners assume that the next step (the sand setting bed) is an opportunity to ‘fix’ uneven spots in the base preparation. In fact, your finished product will mirror the surface of the compacted 2A Modified stone. If your stone base has high- and low-spots, your patio will soon have these same imperfections.
Follow these steps, and you’ll have well-prepared base consistent with the cross-section shown at left. At this point, you're ready for the next step: installing a sand setting bed and placing the pavers.
Stay tuned for our next posts in this series. To see a demonstration of this process, come to Penn Stone at 10am on Saturday April 26 for our free seminar on do-it-yourself concrete paver installation, presented by EP Henry and Cobblestone Landscapes.