How to Build & Construct a Concrete Deck

The curved perimeter of a poured slab used as a concrete deck.

Constructing a deck using concrete is a way to build a long-lasting surface suitable for year-round enjoyment without the construction difficulties normally encountered with traditional wooden deck construction. Using concrete, you can prepare the subsurface and pour the deck slab in one weekend, and a few weeks later construct any deck railing you wish to add in a second weekend. Concrete construction is a great time-saver, and with the wide variety of finishing processes available, the results can be a surface that's both colorful and detailed, while retaining the low maintenance requirements of stone.

Things You'll Need

• Measuring tape
• Lawn flags
• Shovel
• Plate compactor
• Concrete form
• Wooden stakes
• Concrete mix
• Steel rebar
• Concrete squares
• Gravel
• Rebar connectors
• Automatic concrete mixer
• Water
• Screed
• Bull Float
• Edger tool
• Straightedge
• Trowel
• Broom
• Concrete stamp
• Concrete colorant
• Rail kit
• Chalk
• Bolt-down post holder
• Hammer drill
• Concrete drill bit
• Lag bolts and washers
• Socket wrench
• Concrete sealant
• Wood sealant
• Paintbrush

Instructions

Ground Preparation

1. Draw the shape and size of your proposed deck to scale using a pencil on a piece of graph paper. The perimeter of the deck can be any shape desired because the poured concrete used to fill the hole you dig for the deck will conform to the shape of that hole.

2. Measure and mark the contours of the deck into the ground where you intend to construct the deck. Mark the ground according to the deck design using a series of lawn flags planted around the proposed perimeter. Check the measurements against the design plan before breaking ground.

3. Dig a hole within the marked perimeter 6 inches deep using a shovel. Compact the soil at the bottom of the excavation with a plate compactor. You can rent the compactor at a home improvement store or equipment rental shop. The compacted soil reduces the chances of the deck shifting in place at a later date.

4. Build a form for holding the gravel and concrete, lining the hole's edge, from wood, plastic or rubber, following the edge of the hole and held stable and upright with a series of wooden stakes planted against the rear of the form. The form keeps the concrete from blending with the surrounding soil and creating weak patches that may be vulnerable to water damage. Sink the form into the soil, with the top of the form level with the surface of the ground.

5. Measure the square footage of the deck and calculate how much concrete mix, rebar, concrete squares and gravel you need. Concrete should be able to complete the 4-inch thick deck slab, with an additional 10 percent purchased in case of difficulty. You'll need enough rebar to fit the site with a single layer, enough 2-inch thick squares of concrete to hold the rebar in place., and enough gravel to fill 2 inches of the hole.

6. Fill the bottom of the excavation area with gravel, layering the stones 2 inches deep. The gravel acts as a drainage layer for the concrete, preventing cracks. Settle the gravel in place using a plate compactor to prevent it from shifting beneath the concrete.

7. Place the 2-inch square flat pieces of concrete on top of the layer of gravel, one every 4 feet.

8. Place the rebar into the excavation hole on top of the concrete blocks. Line the hole with a piece of the rebar placed every 2 feet along the length of the hole. Place a second layer of bars across the first, one bar every two feet lying perpendicular to the first layer, to create a grid of bars. Twist the rebar connectors around each intersection of the bars to hold them in place. The rebar forms a grid of steel that acts as a concrete unifier and provides extra support for the deck slab.

Pouring the Slab

1. Mix the concrete according to the manufacturer's instructions in an automatic mixer. Begin with the dry ingredients and then add water until the concrete is a smooth, pourable consistency. Transport the concrete from the mixer to the excavation using a wheelbarrow and a shovel. Shovel the concrete into the hole, filling it to the top of the form.

2. Screed the surface of the poured deck level. Place the screed on the top of the form and drag the piece of wood in a sawing motion along the surface of the deck to push excess concrete into voids in the surface, creating a level surface.

3. Drag a bull float along the level surface to distribute the aggregate in the concrete throughout the stone and pull moisture to the surface of the deck to prevent the concrete from curing too quickly and losing strength. Wait for the deck to reabsorb the moisture.

4. Test the deck's firmness by pressing the pad of your thumb into the concrete. Remove your thumb and check the imprint in the concrete. When the impression left is shallow without concrete immediately filling it, you can begin the finishing process of the slab.

5. Run a concrete edger tool between the concrete form and the slab to round off the edge of the slab. Lay a straightedge across the concrete and then cut an expansion joint, using a trowel, one-quarter the depth of the concrete across the slab every 10 feet to keep the slab from cracking as the weather changes. Float the slab again and then smooth the surface of the slab using a trowel.

6. Add texture or color to the slab if desired. Run a broom across the surface of the slab to create a basic non-slip texture, or stamp the slab using concrete stamps to create a pattern. Color the slab by spraying the surface with a concrete colorant. Wait 10 days for the slab to cure and then remove the concrete forms.

Constructing the Rail

1. Construct a rail around the deck using a rail kit and bolt-down post holders. Mark the position of posts on the perimeter of the deck, making sure to place the posts so that the holes in adjacent posts will align with one another. Mark the positions of the posts onto the concrete using a piece of chalk.

2. Place the post holder onto the concrete and mark the position of each bolthole in the concrete. Remove the post holders and then drill holes for the lag bolts to hold the post holders in place into the concrete using a hammer drill with a concrete drill bit attached.

3. Replace the post holders with the holes aligned with those drilled into the concrete. Secure the post holders in place using lag bolts, placing a washer between the post holder and each bolt. Tighten the lag bolts with a socket wrench.

4. Place a post into each post holder and secure them into place by tightening the side bolts on the holders. Mount the rails into the holes on the posts, securing the rails into the posts according to manufacturer instructions.

5. Seal the surface of the concrete deck by brushing on a layer of concrete sealant. Seal the wood of the railing with a layer of wood sealant. Allow the sealants 48 hours drying time before using the deck.

References

• Build Easy: Pouring a Concrete Slab
• Verticon Construction: Concrete Formwork
• Ideas for Deck Designs: Post Anchors - Surface Mounted Solutions

Resources

• Concrete Floor Finishes
• All Things Concrete
• Concrete Network