Rules of thumb for pouring concrete

When you’re preparing for a concrete pour, the hardest part can be figuring out how many bags of mix to buy. Once you’ve calculated the surface area you need to cover (hint: section the pour into rectangles, whose areas are easy to calculate), use these tips to ease the maths.

➽ If you’re framing with 50 x 100 planks, the slab is about 100 mm thick. So you can simply multiply the surface area in square metres by 0,1 to get the volume in cubic metres. Similarly, if using 150 mm planks, multiply ply by 0,15.

➽ One 25 kg bag of mix makes about one-tenth of a cubic bic metre of concrete. So once you’ve got the volume, multiply by 10 to o determine how many bags to buy.

Metal collar stiffens bristles

A parts-cleaning brush, with its stiff bristles, is the best tool for applying solvent to small parts. But if you don’t have one around, you can control the stiffness of the bristles on a normal paintbrush by wrapping them in a collar that effectively shortens their length. Aluminium flashing can be bent to fit tightly around the bristles and held in place with duct tape. Moving it up or down changes the working length of the bristles; the closer to the tip of the bristles you go, the stiffer they’ll be.