lawn patio - Knowledgebase Question

Suffolk, Vi
Question by derrandcanno
April 23, 2009
I'm starting a patio in my yard,15'X10'.How do I lay the concrete foundation?

Answer from NGA
April 23, 2009


Excavate the area with a garden shovel. You will need a 2 inch base of gravel. The gravel layer is meant to prevent your concrete patio from cracking during the freezing-thawing cycle. Make sure you establish a grade that slopes away from the house, for runoff. You can determine the grade by inserting stakes at the high end (up against the house) and low end of the excavation, then hanging a string between them. A line level placed on the string will indicate the present grade. Excavate so as to end up with a slope of about 1 in. for every 4 ft.

Build a form to hold the gravel and concrete. Sink form into the area excavated for the concrete patio. The top of the form should be level with the ground, if you want the concrete patio to be flush with ground level.

Install gravel, tamping it down firmly. Install 2 in.-high flat pieces of rock (rid your garden of some rocks!) as supports for rebar reinforcing, which you must build approximately in the middle of the 4 inch-thick concrete slab.

Install reinforcing rebar to unify the slab. Make a grid by placing them at every two feet both from front to back and from left to right of concrete patio. Unite them with wiring at intersections.

Mix concrete in rental automatic cement mixer, first adding water with a garden hose to the mixer, then concrete, then water again -- until mix becomes a uniform, shiny medium gray.

Pour concrete, starting at end farthest from where your mixer is, building a ramp if necessary. Pour as fast as possible. Preparation is crucial here.

Use a screed to level the surface of the concrete, sliding the screed along the top of the form boards. Pull the screed from one end to the other, drawing off excess concrete.

Look for a watery layer to appear on the surface of your concrete (which is said to "bleed" as it settles). After this watery layer appears, wait for it to disappear before proceeding.

Use a float to even out any lumps on the concrete patio. Sweep it in an arc-shaped motion, keeping the edge at the front of your sweep slightly raised, lest the float dig into the concrete.

Finish the concrete patio surface with design elements. Running a pushbroom over the concrete patio makes a design both attractive and practical: lines that provide visual interest and a slip-resistant surface.

Lay plastic over the new concrete patio. Concrete must be "cured" properly. The key to curing is not letting it dry out too fast. By laying plastic over the concrete patio, you trap the moisture within. Keep the plastic on for a week. Concrete doesn't fully cure for 3 weeks, so even after you've removed the plastic, don't subject the concrete to undue stress.

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