proper depth for patio base?

Hi.  We’ve had 2 contractors recommended on brownstoner give us proposals for installing a new patio in our back yard.  One recommended 2″ gravel plus 1″ of sand as a sub-base.  The other recommended only 1″ of compacted gravel mix.  Everything I’ve read online recommends a 6″ sub-base minimum, with 4″ of gravel plus 2″ of sand.  I’m especially concerned as the patio will be over what is currently a planting bed, so the soils are very loose.  I’m not convinced that mechanical tamping alone will ever get it settled right.  So  are these guys just offering what is standard around here or are they cutting corners that shouldn’t be cut?

suedeshoes

in Driveways, Patios, Sidewalks and Steps 12 years ago

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suedeshoes | 12 years ago

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Thanks for taking the time to respond, everyone.  I understand the detriments of overbuilding, but I have yet to find a single reference online that mentions a sub-base less than six inches.  Many recommend 10″.  I am not suggesting that anyone should go beyond industry standard, just meet it.  The reasons for a deeper base in this situation: this was a garden, so none of the soil is native or settled.  There has to be 6″ of loose soil there.  You can compact it, but then it won’t drain the same way gravel would.  So there could be problems with erosion under the patio, or the water won’t drain through and could freeze in winter causing uplift.  Or due the organic nature of the garden soils, they could decompose over time, or simply compress, and we could be left with depressions.  This is the lowest section of our yard, so a lot of water could end up there and it will need a place to go.  That said, if any of you have direct experience with a thinner sub-base, and you’ve found that it has held up for 5-10 years, I would totally appreciate that info.  Even cutting corners it’s a big expense.  Thanks everyone.

Bond | 12 years ago

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It could be that, or it could simply be that the drainage conditions  don’t call for it.  The most common mistake that amateurs make is overbuilding.  Why stop at 6″ when you can do 10″ and really be safe?  4″ concrete slab in the basement?  Why not a 6″ slab?  The sand is primarily to make setting unven stone or slabs easier.  With man made pavers, it’s much less of an issue.  Why create an environment that ants love?

suedeshoes | 12 years ago

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They’re looking to save the labor cost of removing dirt and hauling in gravel and sand bucket by bucket through our house.  Not the cost of the sand or gravel itself.  Can’t say I blame them, but I don’t want to end up with a slumping patio.

eme1million | 12 years ago

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With the low price of sand or gravel, very hard to understand why one would cut corners here.  I would do the 6 inches and “set it and forget it.”

Bond | 12 years ago

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There is no hard and fast rule of how much to lay down, a lot is going to depend on what is currently there.  Compacting is always a good idea.  I’m not a fan of sand, you will end up with ant nests.  I’d go with rock dust instead. If using a small enough aggragate, you can lay directly on top of that.  It’s a little more work when dealing with bluestone, but with pavers, the uniform size makes installation very easy.  Also, find out how they plan on securing the edges, this is usually where problems arise and you don’t want to find out after the work is done that you hate the look of the edging.

marie-helene | 12 years ago

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Assuming they are using proper patio blocks (at least 2″ deep), a 3″ sub-base should be fine. I am more concerned about drainage and water.  If you are building a patio on a previous planting bed, the area is probably slightly lower than the rest of your yard.  You don’t want to have to clean mud every time it rains.  What are you planning to use between the blocks? ground cover or gravel? If you plan on using gravel, make sure they lay down some landscape fabric between the drainage gravel and the sand, to help control weeds.