How to Lay Concrete Next to the House

Poured concrete, one of the most frequently used construction materials, creates strong foundation walls and flatwork. Laying concrete next to the house, whether you're constructing a sidewalk, or a pad for an air conditioner or patio, requires attaching the new concrete to the existing foundation using steel pins. Once the pins are in place, you can pour the concrete just as you would any other slab.

Vegetation by concrete slab
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Pin the concrete slab to the house foundation.

Step 1

Dig out the soil to a depth of 5 inches where you want to pour the concrete slab. This includes the soil next to the foundation.

Step 2

Cut 2-by-4 dimensional lumber, with a circular saw, to construct the concrete forms. Use a screwgun and 3-inch screws to attach the forms to stakes driven into the ground about 1-foot apart on the outside of the forms.

Step 3

Set the top of the forms at a slant. The surface of the slab should slope away from the house at the rate of a quarter inch per every lineal foot of concrete. For example, if you're pouring a 12-foot wide concrete slab, the outside edge of the slab should be 3 inches lower than the concrete next to the house to encourage drainage away from the foundation.

Step 4

Drill holes, 3 inches deep, into the concrete foundation, spacing them 1-foot apart and at a 45-degree downward angle. Use a concrete drill, fitted with a 1/2-inch bit, and start each hole 2 inches below the future surface of the new concrete. If you're pouring a 4-foot wide concrete pad, you will drill three holes into the foundation.

Step 5

Cut 2-foot sections of steel rebar with a rebar cutter, and drive a 2-foot section into every hole drilled in the foundation with a sledgehammer. Rebar is 1/2 inch thick and it will be a snug fit.

Step 6

Bend the ends of the rebar downward until they are horizontal. This positions the bars in the center of the future slab. This is called pinning.

Step 7

Spread sand in the bottom of the formed area to a depth 4 inches below the surface of the concrete forms.

Step 8

Cut and install additional steel rebar lengthwise and width-wise on top of the sand. Local building codes determine the amount of steel reinforcement you must add to a concrete pour, but the standard is one steel bar every 2 feet in both directions. The bars should extend to within 2 inches of the edges of the forms.

Step 9

Position rebar chairs beneath every place where two bars cross. The chairs have grooves that secure the bars and elevate them off the soil a couple of inches.

Step 10

Pour wet concrete into the forms and spread it out immediately. Use a vibrating concrete screed, which extends across the width of the forms to level the surface of the wet concrete. Place it across the forms, next to the house, turn it on, and pull it evenly over the form boards.

Step 11

Smooth the surface of the wet concrete with a concrete float, which is a large flat plate on the end of a long bar that you will push and pull across the surface of the concrete.

Step 12

Let the concrete begin to harden, and then trowel it with a power trowel to smooth the top once more.

Step 13

Run a concrete edging tool along the edges of the semi-hardened concrete. The tool has a thin lip that fits between the concrete and the wood forms. By sliding it back and forth along the forms, you can form a rounded lip on the top edge of the concrete.

Step 14

Cut control joints in the concrete slab with a concrete saw three or four days after the pour. Control joints generally run about 4 feet apart lengthwise and width-wise. Later, if the concrete cracks, it will usually crack in the control joints.