ConcretingConcreting Tips

  • Set out slab size according to plans for building.
  • Achieve final subgrade level by screeding sand or crusher dust
  • Dig edge beams and footings as required
  • Setup formwork to exact size of slab, take care that formwork is straight and firmly supported to withstand pressure of concrete
  • Lay plastic moisture barrier (seal with duct tape where lapped)
  • Place reinforcement steel (lap as specified by manufacturer) place bar chairs at max 1000mm crs to hold steel at the correct height (check plans for height of reo).
  • Make sure reo is free from formwork by 30mm to 50mm.
  • Check plans for control joints and cut mesh if required.
  • Place pre-mixed concrete (adding water to concrete can lower strength and increase shrinkage – cracking).
  • Generally “slump” shall be 80 to 90.
  • Use a mechanical vibrator when placing concrete, this will release air from the concrete and therefore increase the strength of your slab and minimise the occurrence of shrinkage cracks.
  • Vibrating will add approximately 10% to the volume of concrete required. Machine trowel the floor to required finish (hand trowel finish will generally not provide the same surface hardness).
  • Immediately after finishing floor, cover floor with plastic or spray with curing oil in order to stop evaporation (to cure to design strength moisture is required in the slab)
  • Curing to design strength takes 28 days