Concrete

Published on January 13th, 2013 | by Henri

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Installing a concrete patio floor

Q.   I am considering having a 14-foot by 14-foot concrete patio floor installed in my back yard. It will not be connected to my home or any other standing fixture. In the coming years, I may either build a decking system or a shed on the foundation.

Besides hiring an experienced contractor, I am hoping you can answer the following questions: What should be the desired height of the concrete patio floor? Can the concrete be poured directly on the ground or should the base have crushed stones? What should be in place to prevent any frost damage? Is colored concrete worth the money? Should the foundation include a metal mesh? Any other helpful tips to ensure a long lasting patio floor?

A.   Much depends on the type of soil you have. If the soil is sandy or gravely, your chances of success are much greater. In that case, you can pour what is called a monolithic slab — a slab with thicker edges around the perimeter, in this case to prevent surface water from getting under it.

But if the soil is heavy (clay or silt), you are taking a chance pouring the concrete directly on the existing grade. It is best to have at least two feet of the soil removed and replaced with 1-1/2-inch (egg-size) crushed stones. If your yard is sloping, provide drainage to daylight for the crushed stone bed and be sure to keep the outlet open (it can eventually get plugged by grass, soil or a rodent’s nest).

In either case, the thicker edges of the slab should be reinforced with two ½-inch re-bars, and 6-inch by 6-inch wire mesh should be used in the concrete slab. The mesh should be set on tees specially made for the purpose, as the mesh needs to be approximately in the middle of the pour to be effective.

Have the forms set high enough so that the grade can be brought up the edges of the concrete. This will ensure that the slab ends up with a sloping grade on all four sides to prevent water from seeping under the patio.
For additional safety, you may want to lay 2-inch thick rigid extruded polystyrene insulation under the slab. If you use crushed stones, the insulation should be set on a 2-inch bed of crushed stones before the rest of the stones are spread, but leave about half an inch between the insulation boards so that any water that gets in the stone bed can drain into the soil below.

Get a quote from concrete contractors on pouring the concrete with and without color in it. You can also opt for the options of staining – not painting – the concrete at a later date.

But why would you go to the expense of pouring a concrete patio if you plan to build a deck over it? It only makes sense if you decide to build a shed on it. It seems to me that you should decide the eventual use before going any further.

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