What formwork for garden shed concrete base?

Donpedro

Hi. Need to build formwork for a 3 x 2.5 metre garden shed. Probably overthinking this but would 100x25 mm treated pine work as frame for concrete pour? Dug out base to allow 50mm crushed rock base + 100mm thick concrete slab. Love to hear what others have used. Thanks! Don

MitchellMc

Welcome to the Bunnings Workshop community @Donpedro. It's wonderful to have you join us and many thanks for your question on creating a concrete slab.

Yes, 100 × 25 mm treated pine will work fine for formwork for a slab that size. It’s a common option for small slabs like shed bases.

Because it’s not as rigid as Formply, you’ll just want to support it well with pegs driven into the ground along the outside. Spacing them around every 400–450 mm is a good idea to stop the boards bowing outward when the concrete is poured and vibrated/screeded.

Formply is another option some people use because it’s stiffer and stays straighter, but for a small 3 × 2.5 m slab, the treated pine boards will do the job perfectly as long as they’re pegged securely and set to level.

Your base of 50 mm compacted crushed rock with a 100 mm slab is also a solid setup for a garden shed. Adding reo mesh is a good way to safeguard against cracking.

Here's a helpful step-by-step guide: How to pour a concrete slab.

Please let me know if you have any questions.

Mitchell