Sunday, March 22, 2009

What You Need to Know About Sub Soil Compaction For a Paver System



The base of a patio is just as important as the patio itself. If prepared and installed incorrectly the base could lead to future failure of the paver system.

Depending on what part of the country you are in you will have to take different approaches to sub soil compaction for your paver base. There are a lot of different soil types but to keep it simple I want to focus on soil with high clay content.

My area consists of mostly a clay mix soil. For a patio or driveway we will excavate a few inches of topsoil followed by sticky clay. It seems like this clay is pretty hard and a stable enough base for a patio. The fact is that when water is introduced it is a slimy mess and will squeeze different directions to escape pressure. Having a heavy paver system place on top of it can lead to failure over the years.

How do we manipulate the soil so that it is a stable enough platform for pavers? Simple, through proper compaction.

Every Hardscape contractor has a vibratory plate to compact the base and set pavers into sand. The problem is this type of compactor is not sufficient for the sub soil. A vibratory compactor does just that, vibrates. It exerts a a low amplitude and high frequency. Most range from 1500-5500 Hz. On Grade 8 gravel and other base materials is shakes the stone to fit into each other through the many small hits it produces. Clay is not angular like the base stone and will not settle into itself through vibrations.





A rammer or jumping jack type compactor is what should be used to compact clay. Rammers use low frequency(700-2300Hz) and high stroke blows to compact material through force. It is like taking a sledge hammer and smashing it into the clay compare to a plate compactor which just drops a small weight many times.



By using a rammer in clay type soil you are essentially beating the trapped air and moisture out of the soil. You will see the ground drop an inch or two after ramming. You might even see water come to the surface.




Most contractors in my area do no compaction of the soil before putting in a patio or even driveway. I see paver systems that have failed all the time due to improper soil preparation. Most likely you will not see it in the first couple of years but eventually you will. Areas where you see it the most are around the perimeter of the house 3-4 feet out. After the house is built the foundation is backfilled with chunks of excavated clay. There is all kinds of air pockets when the backfill and they do not compact. 6 months later a Hardscape contractor comes by to put in a patio or driveway and does not compact this soil either. After a rotation of seasons you will see that 3-4 ft band sinking. If the contractor took the extra step to compact the soil this problem would not have occurred. But back they come to perform warranty work.

Yes a rammer can be an expensive tool but in the long run saves you warranty costs and keeps you customers and you image happy. I even use the fact that we compact the soil as a selling point. Most homeowners don’t know much of a paving system and are happy to get a quick education on it. This gives you the opportunity to show why you are different and why your paver system might cost more then the other guys.

If you have questions about sub soil compaction please email me or leave a comment and I would be happy to answer it for you.

5 comments:

  1. We used a rammer yesterday on our clay soil to compact it for dry laid pavers. Most of it compacted perfectly. However, there was one fairly small area that refused to compact. The rammer just sunk in. We would add more soil, try to compact it, and get the same result. When walked on, the soil acted similar to walking on a trampoline. It would sink but once you brought your foot up the soil would return to where it was before stepping on it - almost like there was an air bubble trapped. We dug down to find that about 16" down the soil was saturated and figure this is the issue.
    How do we deal with this area since it is located in the middle of where the patio will be?

    ReplyDelete
  2. Definitly try to find the source of the water. If it is just naturally moist there you can try to remove enough earth and fill with grade 8 or c8 gravel and comoact. Make sure you use geotextile which will help bridge that gap should future problems occur.

    ReplyDelete
  3. When starting to install pavers it is best to snap a true straight chalk line on the surface of the bedding sand or pull a true straight string line above the surface of the bedding sand at the finished elevation of the pavers. This will help as a guide for maintaining straight joint lines and will also allow the installer to make adjustments in the alignment of the pavers.

    Buildings and concrete curbing are generally not straight and should not be used for establishing straight joint lines. The use of string lines is essential to determine the true straightness of the edge as well. As the paver installation progresses, the string lines will help minimize the need for small trim pieces.
    brick pavers orlando

    ReplyDelete
  4. Really buildings and concrete curbing are usually not straight and should not be used for establishing straight joint lines. every Hardscape contractor has a vibratory plate to compact the base and set pavers into sand. The problem is this type of compactor is not sufficient for the sub soil. A rammer or jumping jack type compactor is what really should be used to compact clay. By using a rammer in clay type soil you are essentially beating the trapped air and moisture out of the soil.
    sealing pavement

    ReplyDelete