What Steps Should I Follow to Lay Paving Slabs on a Concrete Base?

Laying paving slabs on concrete bases is a rewarding DIY project that can enhance the aesthetics and functionality of outdoor spaces. Whether you are creating a patio pathway or driveway proper installation is crucial for longevity and stability. 

1. Designing and Planning Your Paved Area

Start by thinking about how you want the space where you will put flat stones to look. Here are the steps:

  • Start with Purpose: First think about what you want the flat stone area for. Is it for people to walk on or for cars to drive over? Do you have a specific shape or curve in mind?
  • Check Water Flow: Make sure water won"t sit on the paved area. Additionally the ground should slope a little (1-2%) so water drains away. Figure out where water might collect and plan for that. If necessary include drains.
  • Digging Depth: Find out how deep to dig based on local rules. In cold areas it"s usually about 4 inches below where the ground freezes. Further this depth keeps things stable during freezing and thawing.
  • Building a Strong Base: For areas with a lot of use like driveways a solid base is essential. Moreover consider a thick domestic concrete slab (5-6 inches) on compacted gravel or poured concrete over footings.
  • Choosing the Right Stones: Explore different types of flat stones. Consider their appearance cost and how suitable they are for walking or driving.
  • Selecting a Pattern: Decide on a pattern for arranging the stones. It could be a simple grid herringbone basketweave or something else. This pattern adds style to the area.
  • Detailed Planning with CAD: Use a computer program (CAD) to draw detailed plans. Include exact shapes stone placements pull points (where you start laying stones) ways to keep them in place and the pattern of the gaps between stones. 

2. Consider Future Steps: 

Think about possible future repairs or changes. Your plan should make it easy to access underneath for any necessary fixes.

  • Durable Edge Restraints: Choose and incorporate sturdy edge restraints. These help in keeping the stones in place over time reducing the likelihood of shifting or unevenness. Well-maintained edges contribute to the longevity of your paved space.
  • Jointing Material Choice: Decide on the material to fill the gaps between the stones (joints). Choose a durable jointing material that suits the purpose whether it"s sand mortar or another option. This decision affects the stability and lifespan of the paved area.
  • Sealing Options: Consider applying a sealant to the finished paved surface. Sealing helps protect against stains and weathering and enhances the overall lifespan. As a result it is an additional layer of defense against the elements.
  • Landscaping Integration: Think about how the paved area integrates with the surrounding landscape. Consider adding greenery to enhance the visual appeal. Install drainage solutions to address practical needs. Further incorporate decorative elements for a balance of aesthetics and functionality.

More info: How to Improve an Ugly Concrete Driveway

3. Get the Ground Ready

Now let"s talk about getting the ground ready for your project.

Digging the Right Hole:

Dig a trench at the right depth. This depth depends on your plan and how cold it gets in your area. Take out anything natural like plants and roots because they can cause trouble later.

Making the Hole Smooth:

Smooth out the walls and bottom of the trench. There must be no water just sitting there. To pack everything down use a machine like a vibrating plate compactor.

Checking Compaction:

The American Concrete Institute (ACI) has rules for how compact the ground should be. They usually want it to be about 85% or more compacted. This makes sure the ground is sturdy and won"t move around.

Keeping it the Same:

Before pouring in the concrete make sure the bottom of the trench stays how it is. Use forms screed pipes with levels or straight tools to check that the ground is exactly right. This is super important for making a strong and even flat area.

Layer the Crushed Stones:

Add layers of clean crushed stones approximately 2 to 4 inches thick. Compact each layer thoroughly before adding more stones. Follow project specifications or local regulations closely. Further opt for materials like gravel mixes Class 1 through 6 to ensure optimal compaction and concrete adhesion. Angular stones in varying sizes from 1/2" down to fines work best.

Ensure Superb Compaction:

Once the final layer is solid and matches the project plan meticulously flatten the sub-base to the precise grade and elevations. Pay special attention to measuring at multiple points as even a slight 1/4-inch variation can impact the final result. Extra care is needed especially at the edges during compaction.

Make it Super Solid:

Confirm that the last layer is exceptionally solid and adheres to project specifications. This step is critical for the overall stability and longevity of your project. Give extra attention to the edges.

4. Install Edge Restraints for Laying Paving Slabs on Concrete

  • After preparing the ground add edge restraints around the border and between sections to control cracks. Use metal plastic or concrete materials buried 3 inches deep in undisturbed soil.
  • For curves use flexible restraints and for straight sections rigid edging works well. Secure them with stakes or tie-backs placed about 3 feet apart along the bottom.
  • Set the initial height of the edging with spacers aligning it with the compacted base. Adjust the height later to match the final paver levels after pouring concrete and installing the sand bed.
  • Properly installed restraints prevent pavers from moving sideways due to freezing thawing or heavy loads. They also help create a neat edge finish for your pattern.
  • Remember to leave specific gaps for drainage and expansion control at planned locations to ensure a stable and durable installation.

5. Install Domestic Concrete Slab

  • After setting up the edge restraints and keeping the ground compact put in steel rebar grids to strengthen the concrete. Use 6” x 12” squares and #4 (#13M) bars or larger depending on expected weight.
  • Overlap the sheets by 8 inches and use rebar chairs on the surface to keep middle mats consistently 2 inches up within the slab depth.
  • Pour concrete at least 5 inches thick following specifications for the project. Use additives that meet ACI and local code requirements are adjusted for weather conditions and have a characteristic strength of 15 - 25 MPA.
  • Level the concrete using screeding pipes or boards adjusting heights and smoothing the surface preferably with power equipment.
  • Create control joints by cutting them where the edge restraints are and throughout the interior in a square pattern with joints around every 100 square feet. The depth of the joints should be one-quarter of the thickness.
  • Follow ACI 308 procedures for proper curing monitoring temperature and checking strength gain during the process with core samples if needed.
  • Avoid foot traffic for a minimum of 72 hours to allow the concrete to set properly.

6. Install Bedding Sand

  1. After the concrete is fully dry spread 1 to 2 inches of bedding sand over the entire slab.
  2. Use concrete sand and limestone screenings following updated ASTM C33 standards for best results.
  3. Level the sand using screed rails and boards making sure not to disturb the concrete underneath. The uneven sand thickness will show on the final surface.
  4. Bedding sand helps smooth out imperfections in the concrete base and shapes around the varied undersides of paving units.
  5. It"s easier to maintain the slab elevation by adjusting this intermediate layer than by shimming each paver individually to account for variable thickness.
  6. Consider using a moisture-resistant geosynthetic fabric rolled out carefully before adding sand to prevent it from seeping into the cracks between slabs.
  7. The thickness and evenness of the sand layer are crucial for achieving a high-quality flat-paved floor.

7. Laying Paving Slabs on Concrete

  • Begin laying paving slabs on concrete close to one edge spacing evenly to plan the final position. Place units rather than sliding to limit disruption of the bedding layer. Ensure tight edges. For most eye-pleasing finishes use randomised slab orientations with aligned edges.
  • Cut partial slabs along edges with special equipment as needed to fit. Rent electric hydraulic or manual cutting tools designed for masonry. Tap gently to level in bedding. Allow space between for joint material.

8. Filling Joints

  • Sweep dry jointing sand across the surface allowing it to funnel into gaps. Sweep and compact repeatedly until filled. Avoid walking on the surface to limit material displacement from joints until properly hardened over several days.
  • For mortar joints dampen slabs first so the mix cures slower and strengthens properly. Use a grout bag for pouring and tooling for a tidy finish. Again limit surface traffic during curing.

Finishing Touches

  • After the joints are firm check if the slabs are aligned well and make small adjustments if needed.
  • Use a broom to clear away any extra stuff and dirt from the surface.
  • For a neat look between the slabs you can pour special sand or fine gravel dust. Press it down into the gaps.
  • If you want to seal the surface follow the instructions from the manufacturer. Wait until it"s fully cured before using it a lot or exposing it to freezing weather.
  • Your finished patio or walkway will look good and last a long time!

Wrap Up 

Laying paving slabs on concrete bases is a rewarding project that adds value and functionality to your outdoor space. Also get in contact with Pro-Mix Concrete for professional assistance.