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Paver patios: failure modes for skipping gravel base

Paver patios: failure modes for skipping gravel base

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  #1  
Old 08-13-10, 12:40 PM
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Location: Sunnyvale, CA, USA
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Paver patios: failure modes for skipping gravel base

I'm installing some pavers (2 3/8 inch thick basalite) in our back yard. I'm wondering what kinds of things will happen if I skip the step where you dig up 6 extra inches of dirt and put in the compacted gravel base. ie, what happens if you just put in an inch of sand over the dirt? My area - San Jose, CA - has no freezing to speak of.

thanks,
Erik
 
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  #2  
Old 08-13-10, 12:43 PM
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The sand and dirt will mix with each other causing dirt to eventually work up between the pavers, the ground will shift and your pavers will be uneven and potentially crack
 
  #3  
Old 08-13-10, 02:48 PM
Join Date: Mar 2005
Location: USA
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mitch is correct about the effects of missing that necessary step. the 2 3/8" thick (80 mm) is appropriate for the use. There is no substitute for building on a solid foundation.

Basalite is probably a member of the Interlocking Concrete Paving Institute (icpi.org) and is a member of the National Concrete Masonry Association (ncma.org) and could have provided the installation instructions or some guidance, if requested. The sites above have technical information on installation.

Apparently, the local distributor did not have the knowledge or information when you asked for it.

Dick
 
  #4  
Old 08-13-10, 03:11 PM
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Originally Posted by Concretemasonry View Post
mitch is correct about the effects of missing that necessary step. the 2 3/8" thick (80 mm) is appropriate for the use. There is no substitute for building on a solid foundation.

Basalite is probably a member of the Interlocking Concrete Paving Institute (icpi.org) and is a member of the National Concrete Masonry Association (ncma.org) and could have provided the installation instructions or some guidance, if requested. The sites above have technical information on installation.

Apparently, the local distributor did not have the knowledge or information when you asked for it.

Dick
There is no shortage of complete instructions, from Basalite, my dealer, or in the wild, describing how to compact the road base, how much to use, etc. My question is not the "how," it's the "why." I can find very little about why. Most of what I can find describes how soil heaves when it freezes and thaws, and this will cause the pavers to settle unevenly. I have seen small installations around here (where it does not freeze) that seem to be holding up just fine.

So, I was wondering what kinds of failure modes people have seen and if they are just in areas where there is freezing.

Mitch describes one failure mode that I hadn't seen described before - the dirt mixes with the sand and work its way up in between the pavers. Thanks. I'm curious - is the extent of the problem here that the dirt will look funny coming out of the pavers? Or does this cause the other things he mentioned - shifting and cracking?
 
  #5  
Old 08-13-10, 03:46 PM
Join Date: Mar 2005
Location: USA
Posts: 6,126
The pavers do not sink or settle. the base under them (not the 1" of setting bed) because it is inadequate. the question of frost heaving is the reason why they perform well in very cold climates, although the majority of use is in more temperate areas. The proper compacted base is necessary and will work in in spite of moisture. You also have to look at what you are building on.

I don't know if you asked about "failure modes" (an engineering term) but all a distributor will give you is the proper and approved that has worked for decades or years before pavers were used in the U.S. The technical failure mode for failure possibilities is not a good subject for a very small project. If you want the detailed support and backup, you may need a truck and another room for the hard copies.

The bottom line is compaction and provision for soil drainage during/after the proper installation including the vibration of fine sand into the joints, although this is commonly omitted on low-tech projects. The same paver shapes (in 100 mm thicknesses) and construction principals have been used internationally, including a 30 acre very heavy duty industrial ship unloading/storage facility at a harbor.

Dick
 
  #6  
Old 08-18-10, 06:10 PM
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Join Date: Nov 2008
Location: mid-west
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small doit yourself paver jobs will do just fine with sand as a base as long as what is below it is stable... like more sand. I have done many that are set in only compacted sand with geo fiber under the bricks some have been in for 15 years and very little settling if any and I live in Michigan. However don't expect to drive over them with heavy implements though as they may settle.
 
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