Concrete Patios: A Well-constructed Patio

Concrete Patio Advice and Construction Help at the John Bridge Tile Forums

John P. Bridge

The Sunbelt, with Houston and surrounding communities included, is patio country for sure. With most of the year amenable to outdoor living, a patio or deck is essential. At our place we virtually live outside in my “jungle” year-round. Patios and terraces, of course, are treasured in any part of the country.

Patios range from simple concrete slabs to elaborate structures with roofs overhead and various stone, tile or brick surfaces underfoot. An outdoor fireplace can be built as an adjunct, and water features or other architectural embellishments can be incorporated. Elaborate lighting systems can be added, and exterior stereo speakers are becoming commonplace, although speakers tend to annoy neighbors.

Patio surfaces can be laid right on the ground as in the case of cement “pave stones,” and various bricks can be installed over sand or decomposed granite. Or, patios can be constructed using concrete slabs as a base. I recommend this latter procedure because of its permanence. Before pouring a slab to be used as a patio, several considerations must be taken into account. As with all things, a little planning up front will save frustration down the road.

First of all, a patio slab should always be constructed with the idea that a roof will be built over it, even if that is not your intent at the time. Somewhere down the line, you may want a roof. This means an adequate footing must be constructed around the perimeter of the slab, one that can support the weight of any roof that might be built over it. It doesn’t cost that much when the slab is being constructed. It would cost considerably more to accomplish retroactively, if it could be done at all without completely re-doing the slab.

Also, if the slab is attached to the house it must be securely tied in to the house foundation or “beam.” Holes should be drilled into the existing concrete beam ,and anchor bolts should be inserted with hooks on their ends. Later the re-bar used to reinforce the slab will be attached to the bolts. This keeps the slab from settling where it meets the house, and it also prevents the new slab from drifting away from the house as the years go by.

Expansion joints must be provided at a minimum of every 10 feet. Eight feet apart would be better. Without adequate expansion joints the slab will develop cracks no matter how well it is constructed. This is due to expansion and contraction caused by the extreme temperature swings we experience in the area — from 100 degrees in summer to near freezing (and sometimes hard freezes) in winter. An expansion joint must also be provided where the slab connects to the house.

If the slab is to be covered with brick, stone or tile, the expansion joints cannot be ignored. We can’t, for example, simply bridge across a joint with the surface material. If we did, the material would loosen or crack the first time the slab segments expanded or contracted. So the joints have to be incorporated into the overall scheme. They must become design features instead of design nightmares. In short, they must be planned.

New slabs must be well reinforced with re-bar. Too often this is not the case. Builders seem to treat patio slabs as lesser structures, not deserving of the same reinforcing that goes into the house slab. This, of course, is a mistake, because when you think about it, an outdoor slab is going to be subjected to more hard use than the house slab itself in many cases . Builders seem to harbor the same disdain for walkways and driveways.

Since existing slabs (without roofs over them) seldom have footings built at their perimeters, roofs cannot be added to them. A new slab can sometimes be poured over the original. If this is not possible, the original slab must be removed and a new one constructed with adequate footings.

If a simple lattice or other lightweight structure is to be built above an existing slab, the footing is not as important. The low weight of the structure will not usually cause a problem. And further, if a problem were to develop, a shade arbor or lattice could be fairly easily dismantled.

A concrete slab constructed outdoors cannot be level. It must be sloped or “pitched” one way or another so that rainwater will run off it. Water will run off if the slab is sloped one-eighth of an inch per foot and the slab is perfectly flat. It is, however, nearly impossible to finish a concrete slab perfectly flat, and a slope of one-quarter inch per foot is more prudent.

If the slab is to be covered with pavers, stone or tile, imperfections in the surface can be corrected with the setting material. Whatever happens, it is a sad state of affairs to end up with a patio that collects water. It is a situation very difficult, if not impossible, to remedy.

Patios do not have to be attached to houses. They can be built anywhere in the yard, and roofs, shade arbors or lattices can be built over them. A series of small seating areas might be spread through the yard, separated by trees, bushes and other plantings. Sometimes small is beautiful. Narrow, curved walkways might connect these intimate retreats, paved with the same materials as the slabs they connect.

Why do patio slabs always have to be rectangles? Answer: They don’t. What’s wrong with a free-form patio slab? A roof can still be built over most of it. A table with an umbrella might be located on another exposed part. Or an outdoor fireplace might be constructed outside (and well away from) the roofed area. Planters (or simple holes in the slab) can be incorporated into the patio. A river might run through it, fed by a gurgling spring and emptying into a small pond.

Imagination should govern your preliminary design. Later, common sense and prudent construction techniques will bring your dreams to fruition.

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