How to Extend a Concrete Patio Slab

Lead Image
What You'll Need
Landscaping paint or marker
Hand tamper
Finely crushed gravel
2x6 lumber
Wooden stakes
2x4 lumber
Stiff-bristled broom
Plastic sheeting

Adding additional space to your concrete patio becomes a necessity if you need more room to entertain or relax. Extending the patio is relatively easy, and it will add the extra area you desire. Of course, you will require additional manpower if you want to pour large amounts of concrete, but if the extension is minor, you can do it yourself with these simple instructions.

Mark the Perimeter of the Extension and Dig

Using landscaping paint, or a marker, mark the perimeter of the extension that you are planning, making sure to keep lines even. Then, take a shovel and excavate the area within the markings to a depth that is roughly nine inches below the level of the current patio. This is necessary since the amount of concrete slab and gravel you'll be adding will amount to this total height.

Compact the Soil

Using a hand tamper, or a similar piece of equipment such as a heavy-duty plate compactor, compact the soil in the planned extension. Be sure to check the level of the dirt periodically with a level or your extension could turn out uneven when it's finished.

Add Crushed Gravel

Crushed gravel

Afterward, add finely crushed gravel over the soil, ensuring that it amounts to about four inches. Level the gravel with a rake or shovel, and compress it, checking it for an even surface as you go.

Build a Form

Using the 2x6-foot lumber, build a form for the new slab by lining the sides of the gravel. Make sure that they lay on the edge on top of the gravel. At the edges, nail the lumber together. Continue lining the lumber on the perimeter until they are the same level as the current patio you are extending, and make sure they’re level. Hammer wooden stakes outside the frame so that they provide support when you pour the concrete into the form. The stakes should be strong and push against the frame.

Pour the Concrete

Pouring concrete

If you are pouring the concrete yourself, it is recommended that you rent a concrete mixer to mix the material according to the instructions on your bag. Easy mixes sold in home improvement stores usually require you to add one gallon of water per bag, but it may vary. Make sure you give the mixer plenty of time to fully combine the batch. Afterward, pour the concrete into the form.

Screed and Stab

After pouring, drag a 2x4 piece of lumber across the width of the form. This will rid the form of any excess concrete as well as show you places where you need to add additional concrete. It is also recommended that you vigorously “stab” the concrete with a shovel to send vibrations that will settle the concrete and help it compact. Continue doing both until you feel that the slab is secure.

Step 6 - troweling wet concrete

Using trowels smooth the surface of the form until it achieves a professional look. If you prefer a more textured, slip-resistant surface, run a stiff=bristled broom lightly across the surface instead.

During the curing process, the concrete must remain wet for a minimum of four days—although it is recommended to leave it untouched for a week. The easiest way to do this is to cover the extension with plastic. After approximately 48 hours, the wood forms may be removed. Then simply wait an extra couple of days and the slab will be strong enough to be subjected to stress, and you can enjoy a long-lasting extension to your patio.