How to pour a concrete slab for a shed

A good concrete slab is needed to create a solid foundation for any garden shed. Pouring this concrete slab properly is important; it will keep the shed level and off the ground which will protect the wood from moisture, rot and mold.

Pouring a concrete slab requires good planning, preparation, tools and building materials. Good quality cement is vital for a solid concrete slab, so choose a high-quality cement for the job.

Materials and tools needed to pour a concrete slab

  • Cement
  • Crushed stone
  • Sand
  • Water
  • Wheelbarrow
  • Shovel
  • Spade
  • Pickaxe
  • Float
  • String
  • Wooden stakes
  • Tamper
  • Wooden formwork
  • Screws
  • Steel rebar
  • Wire
  • Anchor bolts
  • Plastic sheeting

Steps to lay a concrete slab for a shed 

  1. Start by finding a suitable location for the shed, preferably on flat ground. Prepare the ground by removing and grass, roots and rocks. Measure the dimensions of the shed and mark the location of the slab on the ground using string and wooden pegs. The slab should be slightly larger than the shed.
  2. Dig out the area using a spade and pickaxe to a depth of 20cm. Any roots must be removed and the base of the excavation should be level.
  3. Create the wooden formwork using timber planks and screws. This formwork should be about 10cm above the ground around the perimeter of the foundation hole. Ensure that there are no gaps in the formwork.
  4. Next, pour in a 15cm layer of crushed stone and compact it using the tamper.
  5. Mix a batch of concrete using Tembo cement, water and sand. Follow the instructions on the cement bag. Pour in about 5cm of concrete and level it out using a float. 
  6. Cut the steel rebar to size, wet it and lay it on top of the freshly poured concrete. Fix rebar together using thin wire. Pour another 5cm layer of concrete on top of the steel rebar. The concrete should be level with the top of the wooden formwork. Smooth the surface with a float.
  7. Before the concrete dries, insert anchor bolts into the wet concrete at the four corners of where the shed will stand. Be careful when measuring the locations of the anchor bolts as once the concrete dries, they cannot be moved.
  8. Leave the concrete to dry for 24 hours and then remove the wooden formwork. File down any sharp edges of concrete.
  9. Leave the concrete to cure for 28 days. Keep it damp by spraying water on the surface and cover it with plastic sheeting.
  10. Once the concrete has cured, place the wooden shed on top of the slab, securing it to the anchor bolts.


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Written by Joshua Oates


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