9 Simple Steps for a Durable Foundation
A Professional Guide on How To Lay Concrete
Understanding how to lay concrete slabs is essential for anyone looking to build a strong, lasting base for structures like patios, driveways, sheds, or room extensions. Concrete slabs are favoured for their durability, affordability, and adaptability across a wide range of construction projects.
With thoughtful preparation and the right tools, laying a concrete slab can be a manageable DIY endeavour. The process typically includes crucial steps such as site preparation, formwork setup, pouring, levelling, curing, and applying finishing touches.
Quick disclaimer: Although it may look easy and cost-effective, laying concrete slabs yourself can be a meticulous process. Consider hiring professional concreting services to save time and money. Additionally, be sure to read our guide on How Much Does a Concrete Slab Cost to gain a comprehensive overview of budgeting for your DIY project.
Step 1: Plan and Measure the Area
Proper planning is essential before beginning any concrete work. Determine the size, thickness, and location of your slab based on its intended use and load requirements.
Start by marking out the area using stakes at each corner of the proposed slab. Connect these stakes with string lines to visualise the perimeter clearly. Double-check your measurements to ensure accuracy and square corners.
Consider drainage requirements when planning your concrete slab. A slight slope (typically 1/8 inch per foot) away from buildings helps prevent water pooling.
Load-bearing considerations:
- Light use (walkways): 4 inches thick
- Standard use (patios): 4-6 inches thick
- Heavy use (driveways): Minimum thickness of 6-8 inches
Before any digging begins, contact local utility services to have underground lines marked. This crucial safety step prevents dangerous and costly accidents during excavation. Also, check with your local council to see if any of your plans need council approval.
Prepare a proper gravel base beneath your concrete. This foundation provides drainage and helps prevent cracking as the ground shifts naturally over time.
Take the time to evaluate the site for any obstacles, such as tree roots or poor soil conditions, that may require additional preparation. Addressing these issues early saves time and frustration later.
Step 2: Gather the Right Tools and Materials
Before starting your concrete slab project, it is essential to collect all necessary tools and materials for a smooth execution. A well-prepared workspace will save time and prevent unnecessary delays.
Essential Tools:
- Metal screed
- Wooden float
- Magnesium float
- Steel trowel
- Edging trowel
- Jointing trowel (groover)
- Spirit level
- Tape measure
- Shovel
- Wheelbarrow
- Tamper or compacting machine
- Concrete mixer (rental option available)
Required Materials:
- Mixed concrete (pre-mixed concrete or components)
- Gravel base material
- Reinforcing mesh or rebar
- Timber for formwork
- Nails or screws
- String line and pegs
A vapour barrier plastic sheet is recommended to prevent moisture from seeping up through the slab. Consider adding a concrete release agent to your formwork to make removal easier after curing.
The gravel base is particularly important as it provides drainage and a stable foundation. Plan for approximately 4 inches of compacted gravel beneath your slab. A compacting machine can be rented if you don’t own one.
Step 3: Excavate and Level the Ground
Proper excavation is crucial for a durable concrete slab. Begin by removing all vegetation, debris, roots, and organic materials from the marked area. These elements can decompose over time, creating voids that may cause the concrete to crack or settle unevenly.
Dig out the area to a depth of approximately 6-8 inches, allowing space for both the concrete slab (typically 4 inches thick) and the sub-base material. Use shovels and picks for smaller areas, or consider renting a mini-excavator for larger projects to save time and effort.
Once excavated, check the soil condition. If you encounter soft spots, remove the soft soil and replace it with compactable fill. The ground should be firm and stable before proceeding.
Compaction is essential for preventing future settlement. Use a plate compactor for larger areas or a hand tamper for smaller projects to thoroughly compact the soil. This creates a solid foundation that will support your concrete without cracking.
Next, add a 2-4 inch layer of crushed stone or gravel as your sub-base. Spread it evenly across the excavated area and compact it thoroughly. This layer improves drainage and provides additional support for your concrete slab.
Use a long, straight board and a level to check that the sub-base is even across the entire area. Adjust as needed by adding or removing material to achieve a level surface.
If your project requires additional structural integrity, like a concrete driveway with heavy vehicle traffic, this is the stage to install rebar. Position the rebar grid approximately in the middle of where you want to pour a concrete slab to reinforce against cracking.
DIY Plans Gone Off-Track?
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Step 4: Formwork Before Pouring A Concrete Slab
Formwork serves as the mould for your concrete slab, determining its final shape and dimensions. Using straight 2×4 or 2×6 timber boards, cut them to the required length according to your project measurements.
Assemble the timber boards to create a rectangular frame, securing the corners with galvanised nails or screws. Ensure each corner forms a perfect 90-degree angle by measuring diagonally; both measurements should be identical from one corner to the next.
Drive wooden stakes at 1-meter intervals around the outside of the formwork, hammering them securely into the ground. Attach the formwork to these stakes using screws to prevent movement during the concrete pour.
Important checks before proceeding:
- Use a spirit level to verify that the formwork is perfectly level
- Confirm all corners are square
- Ensure the height is consistent throughout
Apply a coat of release oil or form oil to the inside faces of the formwork. This prevents the concrete from sticking to the wood and makes removal easier after curing.
For larger slabs requiring ready-mix cement, create access points where the concrete truck can approach. Position these strategically to minimise the distance for transporting concrete with wheelbarrows and shovels.
Reinforce the formwork with additional bracing if you’re pouring a substantial amount of concrete. The pressure from wet concrete can distort or break poorly secured formwork.
Step 5: Add a Base Layer and Reinforcement
After preparing your site and setting up formwork, it’s time to create a solid foundation for your concrete slab. Start by spreading a 3-4 inch layer of crushed gravel or road base evenly across the excavated area.
Compact this base layer thoroughly using a plate compactor or hand tamper. This creates a stable foundation that helps prevent future settling and cracking of your concrete slab.
Next, consider adding the vapour barrier, a sheet of thick plastic that prevents moisture from seeping up through the concrete. While optional, this barrier is highly recommended for indoor slabs or areas with moisture concerns.
Reinforcement Installation
- Steel mesh (typically 6″×6″ grid)
- Rebar grid (usually spaced 12-18″ apart)
- Mesh chairs or brick pieces (to elevate reinforcement)
Place your chosen reinforcement material over the base layer. The steel mesh or rebar grid should be elevated slightly using mesh chairs or small pieces of brick, positioning it in the middle of the planned concrete thickness.
Reinforcement is crucial as it significantly increases the strength of your slab. It helps distribute weight evenly and prevents cracking due to ground movement, temperature changes, or heavy loads.
When preparing for the concrete pour, ensure your reinforcement doesn’t extend to the very edges of the formwork. Leave approximately 2 inches of clearance from the forms for optimal structural integrity.
Step 6: Mixing The Concrete
Properly mixing the concrete creates a strong, durable slab. To create a workable mix manually, add approximately 1.75 litres of clean water per bag of concrete mix in a wheelbarrow or mixing tub. Pour the dry mix slowly into the water and combine thoroughly until achieving a consistent texture.
When using a concrete mixer, add water first, then gradually add the dry mix while the drum rotates. Avoid pouring too much water. The ideal consistency should be workable but not too runny, similar to thick oatmeal. This process should take no more than half an hour for small jobs.
Choose a cool, overcast day for pouring if possible. Check weather forecasts to avoid rain or extreme temperatures that could affect curing. Early morning is typically best to avoid working in midday heat.
Step 7: Pouring the Concrete Mix
Begin pouring the concrete into your formwork, starting from one corner and working systematically across the area. Work in manageable sections, especially for larger slabs.
Spread the concrete evenly using a rake or shovel, ensuring corners and edges are completely filled. Pay special attention to getting concrete under and around any reinforcement mesh or rebar.
Use a straight piece of timber (screed board) to level the concrete by moving it in a sawing motion across the surface. This removes excess concrete and helps create an even surface for troweling later.
Important Reminder When Pouring Concrete
Make sure to work quickly once pouring begins, as concrete typically remains workable for only 1-2 hours, depending on conditions. Having helpers for larger projects can make this process much more manageable.
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Our concrete removal team demolishes and disposes of the material responsibly, making way for a fresh pour. Call for a free quote: 1300 826 505.
Step 8: Screed, Float, and Finish the Surface
After pouring the concrete into your formwork, it’s time to create a smooth, durable surface. Begin by screeding the concrete immediately after pouring. This involves using a straight piece of lumber (the screed board) in a sawing motion across the top of the formwork to level the concrete.
Once the concrete is level, use a bull float to smooth the surface. Push the bull float across the concrete to remove high spots and fill voids. This step embeds larger aggregates and brings cream to the surface.
After the bleed water disappears from the surface, use a hand float to further smooth the concrete. This creates a more refined finish and prepares the surface for final texturing.
Now is the time to create control joints. These planned cracks should be cut at intervals of 2-3 times (in feet) the thickness of the slab in inches. For example, a 4-inch slab needs joints every 8-12 feet.
Use an edging tool along the formwork to create rounded edges. This prevents chipping and creates a clean, smooth, finished concrete appearance.
For the final texture, choose a finish that suits your needs:
- Broom finish: Creates a nonslip surface ideal for driveways and walkways
- Trowel finish: Produces a smooth surface perfect for garage floors
- Stamped patterns: Decorative option that mimics stone, brick, or other materials
Allow the concrete to cure properly according to the manufacturer’s instructions before removing forms or applying weight to the surface.
Step 9: Cure the Concrete Properly
Proper curing is essential for your concrete slab to reach its full strength and durability. This final step prevents premature drying, which can cause cracking and weaken the overall structure.
Curing begins as soon as the concrete has hardened enough that your finger leaves only a slight impression when pressed on the surface. This typically occurs within 24 hours after pouring.
Why Curing Matters:
- Increases concrete strength
- Improves wear resistance
- Reduces cracking and shrinkage
- Enhances durability against freeze-thaw cycles
Effective Curing Methods:
- Water Curing – Spray the surface with water several times daily or cover it with wet burlap
- Curing Blankets – Special moisture-retaining covers that insulate and maintain consistent hydration
- Curing Compound – Liquid membrane that seals moisture in; apply with sprayer after finishing
The concrete should be kept consistently moist for at least 7 days. While the slab will be hard enough to walk on after about 48 hours, it continues gaining strength for up to 28 days.
To control cracking during the curing period, avoid rapid temperature changes. In hot weather, shield the slab from direct sunlight or schedule your pour for cooler parts of the day.
For best results, restrict heavy traffic and loads on your new concrete slab for the first week. Full vehicle traffic should wait at least 7-10 days, depending on conditions. For more detailed information, read our blog on How Long Does Concrete Take to Set.
Final Tips and Common Mistakes to Avoid
Proper preparation prevents most concrete slab problems. Before beginning your project, ensure you have all the necessary tools and materials ready to avoid interruptions during the pouring process.
Lack of subgrade preparation is a common mistake that leads to cracking and settling. Always compact the soil thoroughly and add a proper gravel base before pouring concrete.
Weather conditions significantly impact concrete settings. Avoid pouring during extreme temperatures without taking appropriate precautions. In cold weather, use warm water in your mix and protect the slab with insulating blankets.
Sloppy formwork often results in uneven edges and weak structures. Take time to secure forms properly, checking that they’re level and braced adequately to withstand concrete pressure.
Rapid drying can compromise the strength of your slab. Keep the concrete moist during the curing process by covering it with plastic sheeting or applying curing compounds.
Poor compaction leads to air pockets and weakened concrete. Use proper vibration techniques to remove air bubbles and ensure concrete fills all spaces within the formwork.
Incorrect mixing ratios result in weak or crumbly concrete. Follow the manufacturer’s specifications precisely when combining cement, aggregate, and water.
Don’t rush the finishing process. Premature finishing can trap bleed water beneath the surface, causing scaling and dusting problems later.
Always consider drainage when designing your slab. Improper slope can lead to water pooling and potential damage over time.
Get Started with Superior Concrete
From garden paths to industrial slabs, Superior Concrete’s licensed and insured team ensures durability with premium materials, modern equipment, and expert craftsmanship. Review our completed projects in our gallery and judge for yourself what we can do for your property.
Why choose Superior Concrete?
- Free on-site quotes & consultations
- High-grade concrete mixes
- Efficient, modern tools
- Transparent pricing, no hidden costs
Skip the hassle of DIY formwork and pouring. Contact us for a free quote today or call 1300 826 505.
