Pouring Concrete

DEAR MIKE: I want to install a concrete patio in my back yard, where the builder put a small pad. I've never worked with concrete, but my friends are willing to help. The patio would measure 10X14. Is this a project I could handle? -- Scott P.

DEAR SCOTT: Concrete is hard, dirty work, and mistakes have a way of becoming permanent. There's also the added pressure of time, because once the concrete truck arrives, the clock starts ticking and the concrete is hardening.

Now that I've given you reason to doubt, know that the size of patio you're considering is pretty small in the world of flatwork. If you still want to do it yourself, then read on; you're a man among boys.

First, use a pry bar or a pickax to lift the pad, then use a sledgehammer to break it into pieces. Wear eye protection, and protect nearby windows with plywood because concrete flies apart when it's smacked.

Now you're ready to build a form for the patio. The materials needed for this are available at a home center for less than $30. You'll form the three sides out of 1-inch-by-4-inch wooden forms and you'll need metal stakes to support the form boards. Buy enough stakes to support the perimeter of the form every three feet.

When you start forming the patio, remember to slope it away from the house to keep water away. The sides of the form should slope one-quarter inch for every foot. So, if your patio is 10-feet long, it should slope 2 1/2 inches.

Drive the stakes into the ground every three feet on the outside of the form, and attach the form boards to the stakes using double-headed nails. A pro would leave the third form board off so that he could wheel the concrete right up to the exact spot where he wants it, but you can leave the board on to lessen your anxiety. Just dump the mud over the form board and use a flat shovel or a rake to move it.

When you order the concrete, you'll be charged a minimum load charge (called a short load) for a partial truck. Ready-mixed concrete costs around $70 per cubic yard and the short load charge will be around $50.

To determine how much you'll need, figure out the cubic footage, then convert that figure to yards by dividing by 27. For your patio, multiply the length (14 feet) times the width (10 feet) times the depth (4 inches or .33 feet). 14 x 10 x .33 = 46.2 cubic feet. This figure divided by 27 equals 1.71 cubic yards. You'll need 1.71 cubic yards of concrete. I would order two yards though to make up for an uneven base or for a wheelbarrow that tips over.

Now it's time for your friends and the concrete truck to arrive.

Use a garden hose to wet the ground inside the form. Also wet the base of the house, which makes it easier to remove any concrete that splashes onto it. Start wheeling in the concrete and dumping it inside the form. Begin near the house and work your way out. Use a steel rake or a flat shovel to push it into the corners and along the boards. Make sure you pour the concrete slightly higher than the forms.

Next, level the concrete with a screed board (a two-by-four works well). Rest the screed board on the forms and, using a sawing motion, pull it toward the end of the pour. If there are any low areas, fill them in with concrete and screed the area again. Use a hammer or your foot to tap the sides of the boards to fill in any voids.

Wait until there is no bleed water (water that rises to the surface of fresh concrete). If you work the concrete when bleed water is present, you'll weaken the surface. Instead, wait until the concrete absorbs the water.

By the way, concrete finishing tools can be rented for $5 to $10 each per day.

Use a bull float with an extension handle and draw it over the fresh concrete. This forces down large gravel pieces and leaves gravel-free concrete at the top for smooth finishing. Work in the opposite direction of screeding. Make sure to lift the leading edge of the float to avoid digging into the concrete. Lift the front edge as you push it away, and the back edge as you pull it back.

You can start hand tooling the concrete when you can't push your thumb more than one-quarter inch into it. Use a magnesium hand float (mag float) to smooth out the surface in sweeping motions, remembering to lift the leading edge. Use light pressure at first, but as the concrete hardens, you'll need both hands to scrub out the imperfections.

Use an edging tool to round over the edges of the outside corners. Use short back-and-forth motions to round over the edge. Use the mag float to smooth out any ridges caused by the edger.

Next, cut control joints with a groover, which creates a 1-inch-deep groove in the concrete and helps control cracks. The control joints should be spaced about every 6 feet. Again, use the mag float to smooth any ridges.

Finally, get a concrete broom and rest it on the far side of the patio. Pull it toward you and off the edge of the form. If the texture is too rough, smooth it out with the mag float and wait 15 minutes before trying again.

Wait several hours after the concrete has set, then carefully remove the form boards.

This job can be a true test of friendship, so be sure to have plenty of pizza on hand. As a bonus, you might let your friends carve their initials in your new patio. This is best done at the time you are edging the corners.

Concrete takes about a month to reach full strength. You can help by spraying it with water three times a day for at least a week.

A word of caution: concrete is caustic and can leave chemical burns on skin. Never work in clothing that is wet with concrete. 

Need Help? Contact Us!