Shed Slabs on the Tablelands: What a Proper Shed Floor Actually Needs

Short answer: a shed slab is the one pour where what is underneath matters more than what is on top. Get the base compacted, the thickness right for what is going to sit on it, the steel sized to the job and the water moving away from the shed, and the floor stays flat for decades. Skip any one of those and the first wet season finds it. Here is what a proper shed floor on the Tablelands needs, in the order it gets built.

Start with what is going on the floor

A garden shed and a machinery shed are not the same slab. A floor for a mower and some tools needs far less than a floor that has a tractor, a truck or a hoist on it. The first question we ask is what the heaviest thing on the floor will be, and where it will sit, because that decides the thickness, the steel and whether the edges need thickening. Tell your concreter honestly. A slab poured for a car and then used for a loaded truck is the most common shed slab failure we see.

The base is the job

On the Tablelands the ground moves. Red soil holds water, the wet season saturates it, and a slab poured straight onto uncompacted or wet ground will follow the ground when it moves. A proper shed slab sits on a compacted base of road base or crusher dust, levelled and compacted in layers, with a plastic membrane on top to keep ground moisture out of the concrete. That base is also what stops the slab from sinking at a corner where a machine always parks.

Thickness, steel and edges

• Thickness. A domestic shed floor and a machinery pad call for different slab thicknesses. The heavier the load and the wetter the site, the thicker the slab, and the thickening goes where the load actually sits, not spread evenly out of habit.
• Steel. Reinforcing mesh sized to the load, set at the right height in the slab rather than lying on the ground, and heavier bar in the thickened edges and under any post or hoist position. Steel does not stop concrete cracking; it holds the cracks tight so they stay hairline and the slab stays in one piece.
• Edge beams. The edges of a slab carry the shed frame and cop the most weather. A thickened edge beam keeps the perimeter from breaking away and gives the shed posts something solid to bolt into.
• Control joints. Cut at the right spacing so the slab shrinks along lines we chose rather than somewhere random. A crack in the bottom of a joint is the slab doing its job.

Drainage: the part everyone forgets

A shed slab that sits below the surrounding ground becomes a pond in February. The finished floor should sit above the ground around it, with the surface falling slightly toward the door or a drain so water that blows in runs out again. Outside the slab, the ground should fall away from the shed on every side, and a spoon drain or ag pipe on the high side stops the wet season running under the slab. Drainage is decided before the pour, not after the first flood.

The surface

A shed floor wants a finish that suits the use. A steel-trowelled finish is smooth, easy to sweep and easy to roll a jack on, and it is the usual choice for a workshop. A light broom finish gives grip where the floor gets wet or where machinery drives in and out. Tell us how the shed will be used and we will finish it to match. If it is a working floor, a sealer once it has cured keeps oil and stains from soaking in.

How to brief your concreter

• The heaviest thing that will ever sit on the floor, and where
• The shed size and where the posts land, so the edge beams and hold-downs line up
• What the ground is like and where the water goes when it rains hard
• Whether the floor needs to be smooth, gripped or sealed
• When the shed is being erected, so the slab has cured before the frame goes on

Give us those five things and the quote will be for the slab you actually need, not a guess. We pour shed slabs, workshop floors and machinery pads across the Atherton Tablelands, from Malanda and Atherton to Yungaburra, Herberton, Millaa Millaa and the properties in between.

FAQ