How to pour a shed slab. This is part 3 of a simple guide to what you might need to do or what you could encounter when organising your sheds concrete slab. For this guide we will assume that the location of the shed is already a level or near level site. Go to part 2. Go to part 1
Staring at one end pour concrete into form work and trenches making sure each new load of concrete is well mixed into the previous load. Level the surface of the concrete with a screeding board by moving the board with a sawing and chopping motion. This helps to compact the concrete. A vibrator should be used in the deeper sections like the beams and trenches. Poke the vibrator into the trenches every ½ a metre or so and vibrate till no more bubbles appear and the concrete settles. Be careful not to move the trench mesh or damage the membrane.
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Once the compacting and screeding is done the slab should be roughly floated to give a smooth surface. After floating the slab should be left to set hard enough for a man standing on his heels to sink no more than 5mm into the concrete. Whilst setting the bleed or free water will rise to the surface and evaporate. If it is a cold day and the free water is not evaporating the it might be necessary to drag a hose or rope across the surface to pull the water clear. Under no circumstances should you cast cement dust or sand on the water, this will weaken the surface and cause flaking. On large slabs a helicopter is the best way to get a good finish. Start at the end where the concrete was first laid and work your way back and forth across the slab down to the end. Return to where you started and do again this time working down the length. If you don’t have a helicopter steel and wooden floats can do a good job too and should also be used over the whole surface twice.
Cure the Slab
If your shed slab dries to fast it can lose strength, crack more than it needs to or go powdery. Curing the slab involves keeping some moisture in the drying concrete longer therefore allowing the concrete to gain its full strength. The most popular method to help slow the drying process is to cover the slab in plastic, hold it down with planks and or bricks and keep that in place for a few days. Sometimes in warm weather some additional water is carefully applied under the plastic. The covering of a slab with plastic also prevents possible damage from rain which can damage the surface of the slab causing it to go powdery and lose it surface. In hot weather it is a good idea to ask for your concrete to have an additive to help slow the cure.
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