The Slab

The Slab sits over the Pit. Around Jozini they tend to be made out of a 10cm thick slab of reinforced concrete with some steel rods inside them to provide additional strength. To cast them, wet concrete is poured into a wooden mould which sits over the pit, and when the concrete sets, the mould is removed.

But... I want to avoid the trouble of pouring concrete in someones back garden out in the rural areas. I want to be able to turn up at the customers with the whole loo, dig a pit, put it all in place and then go home!

So, I was looking for a way to cast the Slab in a factory, and make it light enough so that it can be stuck in the back of a buckie/ute/4x4/what Jo Mangel was always driving in Neighbours, then carried it into place over the pit.

Then I stumbled upon the SanPlat website. This had instructions for building a Dome-shaped slab which allows you to have a much thinner slab (4cm) and no steel reinforcement! And here's why...

Concrete is strong when squashed (compression) but pretty useless when stretched (tension), If the Slab was flat, then the top half of the Slab would be in compression, but the bottom half of the Slab would be in tension :-( so you would need to cast steel rods into the bottom half of the flat slab for additional strength (steel is good in both tension AND compression).

With our Dome Slab, by virtue of its shape, both the top half and the bottom half the Slab is in compression so you don't need the steel. (Trust me on this one) Hurrah for domes, and the same goes for arches too!

So, the Dome shape reduces the weight of the slab to about 200kg. Which is still pretty heavy eh? But, if one person lift 50kg then we're talking four people carrying the slab, which seems ok.