Pouring a 3x3 Metre Concrete Slab
A 3x3 metre slab is one of the most common sizes for Australian backyard projects. At 9 square metres, it's the perfect size for a small garden shed, outdoor storage area, or compact patio space. This guide covers everything you need to know about calculating and pouring concrete for this popular slab size.
Standard Specifications for a 3x3 Slab
For most residential applications, a 3x3 metre slab should be 100mm thick. This provides adequate strength for light structures like garden sheds, outdoor furniture, or foot traffic. The standard 100mm thickness has been the Australian residential benchmark for decades, offering a good balance between material cost and structural integrity.
Site Preparation is Critical
Before pouring any concrete, proper site preparation makes the difference between a slab that lasts decades and one that cracks within months. Start by excavating the area to approximately 150mm depth, allowing for 50mm of compacted road base beneath your 100mm slab. Remove all organic material, roots, and soft spots. Use a plate compactor to achieve proper compaction of both the subgrade and the road base layer.
Formwork and Reinforcement
Set up timber formwork around the perimeter using 100x50mm timber for a 100mm slab. Ensure the forms are level and properly braced to prevent movement during the pour. For a 3x3 slab, SL72 reinforcement mesh is recommended. Position the mesh on bar chairs approximately 40mm from the bottom of the slab to ensure proper concrete cover.
Mixing and Pouring Tips
For a slab this size requiring approximately 1 cubic metre of concrete, you have two options. Mixing bags by hand requires around 108 bags of 20kg concrete mix, which is significant physical work. Alternatively, ordering ready-mix concrete is often more practical for this volume. Most concrete suppliers have minimum orders around 0.5 to 1 cubic metre, making this size ideal for a ready-mix delivery.
Curing Your Slab
After finishing, keep the concrete moist for at least 7 days. Cover with plastic sheeting or use a curing compound. Avoid walking on the slab for 24-48 hours and don't place heavy loads for at least 7 days. Full strength develops over 28 days, so plan your project timeline accordingly.
Need Different Dimensions?
Use our concrete slab calculator to enter your exact measurements and get instant results. You can also compare bags vs ready-mix costs for your specific project volume.