raised patio

Old 07-07-06, 03:20 PM
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Post raised patio

I currently am in the process of builiding a raised patio. I finished the trench for the patio wall and backfilled this area with 3/4 trap rock. I live on the water and most of my yard is made up of clay and rock. As I excavated the trench I removed all the excess clay and soil to the inside of the raised patio. I have three questions: 1) Is it necessary to remove the clay/soil from the inside or can I just add the base and compact? 2) I live in the northeast and receive a fair amount of rain, what kind of drainage system should I have, if any? I plan to use an interlocking brick for the wall and pavers for the top. 3) I am getting mixed messages on backfill, which is more appropriate, 3/4 trap rock or some kind of aggregate? Thanks for your time. DP
Old 07-07-06, 05:53 PM
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raised patio

I assume you are buildin a retaining wall out of segmental concrete retaining wall units and a patio out of interlocking concrete pavers. Let me know if this assumption is wrong.

Much of the recommendation will depend on the height of the patio surface above the water level or the wtare table. I assume the "trap rock" you are dealing with is a very hard, durable crushed igneous rock that usually does not have too many fines. It is an excellant material if used properly.

Water is the enemy of clay and can destroy all its strength. In wet conditions, it would be good to have 6" of 3/4" trap rock (compacted if possible, but not likely without any fines. Then use 4 to 6" of base (crusher run, etc. - clean compactable granular material) to crush and fill the traprock voids. After this, spread the usuall 1" sand setting base for the pavers. Install the pavers according to the maufacturers suggestions. The purpose of the crusher run is to provide strength and prevent (a filter) the setting bed sand from filtering down into the voids in the trap rock.

This may seem excessive, but clay and water in a northern climate are difficult conditions. It is good that interlocking pavers (WITHOUT MORTAR) are resiliant enough for your application.

The whole idea is to get a strong base (trap rock) choked with base material to distibute the loads and let the paver surface act a single, non-rigid pavement.

Subsyrface drainage is always a wise investment. You could increase the traprock thickness slightly and embed perforated drain pipe. You will have to find and exit for the water.

You might want to look at the Versalok site on the web. They had some good photos of waterside applications of pavers and retaining wall block. the other national retaining wall brands also have good sites.


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