Building A Concrete Patio Bench: A Step-By-Step Guide

Building a concrete patio bench is a great DIY project to add an elegant and durable touch to your backyard, patio, or porch. It is a challenging task that requires careful planning and execution, but the end result will be a sturdy and long-lasting piece of outdoor furniture. This introduction will provide an overview of the tools, materials, and steps needed to build a concrete patio bench, as well as some tips and tricks to ensure a successful project.

Choosing the right concrete mix

The concrete mix you choose for your patio bench project is crucial, as it will determine the strength, durability, and overall success of your bench. Here are some detailed instructions and considerations to help you choose the right concrete mix:

Type of Concrete Mix

For a concrete patio bench, it is recommended to use a high-strength concrete mix designed for durability and strength. Look for concrete mixes that are rated for at least 5000 PSI strength. This will ensure your bench can withstand the weight and the elements. Avoid using fast-setting concrete if you are a beginner, as it requires working at a much quicker pace. Instead, opt for regular speed concrete mix, which gives you more time to work before it sets.

Amount of Concrete Mix

Calculating the amount of concrete mix required is essential to ensure you don't run out during the project. Measure the dimensions of your bench mold and use a concrete calculator to determine the volume of concrete needed. For example, for a bench seat measuring 48 inches by 16.5 inches and legs measuring 16 inches by 15.5 inches, you will need approximately five 80-pound bags of concrete mix.

Mixing Concrete

When mixing concrete, always wear protective gloves and clothing to avoid skin contact. Follow the instructions on the concrete mix bag for the correct ratios of concrete to water. As a general rule, use about 6 pints of clean water for each 80-pound bag of concrete mix. Mix the concrete with a garden hoe or shovel until you achieve a stiff, moldable consistency. Be sure to mix in small batches and add water gradually to avoid making the mixture too runny.

Adding Colour

If you want to add colour to your concrete bench, use a liquid cement colour additive. Add this to the water before mixing it with the concrete. For a deep grey finish, you can use a charcoal-coloured additive. However, keep in mind that the colour you choose may impact the overall aesthetic of your bench.

Working with Concrete

Concrete can be messy and challenging to work with, so it's essential to be prepared. Always mix your concrete in a clean, well-ventilated area. Use a wheelbarrow or large plastic tub for mixing, as it makes it easier to pour the concrete into the molds. Additionally, be mindful of the setting time of the concrete. Depending on the temperature, it may take 5-7 days for the concrete to dry completely.

Building the mould

Building a mould for your concrete patio bench is a crucial step in the process. Here is a detailed, step-by-step guide to constructing a sturdy and smooth mould:

Materials:

First, gather your materials. You will need plywood for the mould. The type of plywood you use is important. Shuttering plywood, specifically designed for making moulds, is recommended for its smoothness and water resistance. However, it is also expensive. An alternative is to use melamine board, which has a smooth surface but is not water-resistant on the sides. You will also need screws, a drill, a silicone sealant, and some type of release agent to ensure the concrete doesn't stick to the mould.

Cutting and Assembling:

The next step is to cut your plywood or melamine board to the desired size and shape. If you are using plywood, cut the pieces with a table saw or a circular saw to ensure straight cuts. If using melamine board, you can ask your local hardware store to cut the pieces for you. For curved shapes, clamp down two side pieces on top of each other and cut them together to ensure they are identical. Once you have all your pieces, assemble them by screwing them together. Use plenty of screws to ensure the mould can withstand the pressure of the concrete.

Reinforcement:

Before filling the mould with concrete, you will need to add reinforcement to ensure the strength of your bench. Rebar is a common choice for reinforcement. Cut the rebar to the correct size, placing it with an offset of at least 4 cm from the concrete surface to prevent rust and spalled concrete. Make sure the rebar is placed as far down in the seat as possible to bear the weight when someone sits on the bench.

Sealing and Release Agents:

If you are using melamine board, apply a silicone sealant at the joints to make them waterproof. You can also use masking tape to create a tight seal. If using plywood, seal the interior of the mould with acrylic varnish and let it dry before applying a film of paste wax over the inner form.

Finally, apply a release agent to the mould to ensure the concrete doesn't stick. You can use special release agents, or alternatives like silicone spray, olive oil, WD40, or petroleum jelly.

Now that your mould is built, you are ready to mix and pour your concrete to create your patio bench!

Adding rebar

Rebar is a crucial component in constructing a concrete patio bench, providing reinforcement and ensuring the concrete's longevity. Here's a detailed guide on adding rebar to your project:

• Rebar Selection and Preparation: Choose rebar with the appropriate thickness (e.g., 3/8" or 1/2") and length for your bench. You can purchase rebar from a hardware store or use a piece of an old fence, ensuring it's cut to the correct size.
• Placement and Spacing: Place the rebar with an offset of at least 4 cm from the concrete surface to prevent rust and spalled concrete. Position the rebar as far down in the seat as possible to manage tensile forces when someone sits on the bench.
• Legs and Supports: If your bench design includes separate legs, create a loop of rebar and attach it to the slab, then loop it up for the legs. This will help attach the two components securely.
• Wire Mesh and Reinforcement: Use wire mesh to reinforce the concrete, cutting and bending it to fit your bench shape. Bend the rebar to create a ring around the edge and tie it to the mesh. For wider benches, use extra rebar lengthwise for added support.
• Avoid Overlapping: Avoid overlapping rebar sections to prevent creating tight spots that can lead to voids in the concrete. Use wire to tie the rebar securely to the frame, ensuring it doesn't move during the concrete pour.
• Final Checks: Before pouring concrete, double-check the placement of the rebar and ensure it's level, especially for the legs. Cut any wires holding up the rebar below the surface to avoid exposure.

Remember, rebar plays a vital role in strengthening your concrete patio bench and managing cracks. Take your time during this step to ensure a sturdy and long-lasting final product.

Mixing concrete

Choosing the Right Concrete Mix

Before you begin, it's important to select the right type of concrete mix for your project. For a concrete patio bench, Quikrete's 5000 concrete mix is highly recommended. This specific mix is known for its high early strength, ensuring that your bench will retain its structural integrity once the forms are removed. The 5000 formula will guarantee a sturdy and crack-free bench. You will need three 80-pound bags of Quikrete 5000 for the top and legs of the bench.

Gathering the Necessary Tools and Materials

To mix and work with concrete, you'll need the following tools and materials:

• Mixing tub or wheelbarrow: A large container to mix the concrete in.
• Shovel: Used for scooping and mixing the concrete.
• Garden hoe: Assists in mixing the concrete.
• Water: Essential for mixing with the concrete mix.
• Protective clothing: Wear long sleeves, gloves, and eye protection to avoid skin and eye contact with wet concrete.
• Gloves: To protect your hands from the cement, always wear gloves when handling concrete.
• Measuring tools: Accurately measure the amount of water and concrete mix required.
• Rebar: Four-foot lengths of rebar will provide structural support for your bench.
• Wooden blocks: These will be used to grip into the concrete and keep the weight down.

Mixing Instructions

Now, let's get into the step-by-step process of mixing concrete:

• Calculate the amount of concrete needed: Determine the volume of your bench mold and calculate the required amount of concrete accordingly.
• Prepare the mixing area: Set up your mixing tub or wheelbarrow on a level surface and have all your tools and materials ready.
• Measure and mix: Follow the instructions on the concrete bag for accurate measurements. Start by calculating the amount of water needed, then add about two-thirds of it to the mixing tub or wheelbarrow. Gradually add the concrete mix while continuously stirring with your shovel or hoe.
• Consistency check: Your concrete mix should be thick but spreadable. It should hold its shape when shoveled but also be easy to spread with a trowel.
• Add colour (optional): If you wish to add a darker colour to your concrete, you can use a pigment powder. Be sure to mix it thoroughly to avoid a patchy appearance.
• Final water addition: Once the concrete is mixed, add the remaining one-third of water to achieve the proper consistency.

Remember, always wear protective gear when working with concrete, and be mindful of the time as concrete can begin to set within an hour in warm weather. Now you're ready to pour your concrete into the molds and continue building your patio bench!

Pouring concrete into the mould

Now that your mould is ready, it's time to pour in the concrete. This part of the process is crucial, as it will determine the strength and smoothness of your bench. Here are some detailed instructions to guide you through the process:

Before you begin pouring, ensure that your mould is level. This is important to achieve an even surface for your bench. Use a release agent or a mould release spray to make it easier to remove the concrete bench from the mould later on. There are special release agents available in the market, but you can also use common household items like silicone spray, olive oil, WD40, or petroleum jelly.

Calculate the amount of concrete mix you will need based on the size of your mould. A standard 25kg bag of concrete will yield approximately 12 litres. For a stronger bench, consider using Quikrete's 5000 concrete mix, which has high early strength and will ensure a sturdy, crack-free bench. You will also need to wear protective clothing, including gloves and eyewear, to avoid any skin contact with wet concrete.

Prepare your concrete mix by following the instructions on the bag. Mix the concrete with water using a shovel or a mixing tool. If you want to add colour to your bench, use a concrete pigment or liquid cement colour. Be sure to wear gloves during this process, as the cement can dry out your hands.

Start filling the mould with concrete, spreading it evenly and pressing it into the base of the mould. Use a steel finishing trowel to level the concrete, but be careful not to overwork it. Scrape off any excess concrete with a straight board.

To get a smooth surface and remove air bubbles from the concrete, you can use several techniques. Tap the mould rapidly with a hammer, especially the sides and bottom, to bring the air bubbles to the surface. You can also use an electric sander or a drill hammer to vibrate the mould, which will help bring the air bubbles up.

Once the mould is filled, cover the legs or any open areas with plastic foil to prevent the water in the concrete from evaporating. Let the concrete cure for several days—at least 40 hours or up to five days—before demoulding. This will give it enough time to harden and strengthen.

After the concrete has cured, it's time to remove it from the mould. Carefully unscrew the mould and use a joint knife or a similar tool to gently separate the concrete from the wood. Be gentle, as the concrete is still fragile at this stage.

Your concrete bench is now ready! You can smooth out any rough edges with an abrasive or a sander if needed. If you want to expose the aggregate (small stones) in the finish, you can use a wire brush to gently remove the smooth concrete layer.

Frequently asked questions