Formwork and concrete casting

Measure and set out the foundation lines from one fixed starting point, and check squareness by measuring the two diagonals — if they are equal, the figure is square. Use the 3-4-5 method to set the right angles. A skewed setting-out here carries through the rest of the building.

Excavate to a firm, load-bearing base at the depth and width specified by the project. The bottom must be load-bearing and free of loose soil and water so the foundation does not settle. Frost-free depth and bearing capacity are design requirements — follow the drawing.

Set the formwork plumb and brace it firmly so that it can hold the concrete pressure without bowing out — fresh concrete is heavy and presses hard on the sides. Check plumb, alignment and internal dimensions, and that the formwork is tight so that cement slurry does not leak out.

Never underestimate concrete pressure — formwork that bows during casting cannot be straightened afterwards.

Calculate the concrete volume as V = L · B · H with all dimensions in metres so the result is in m³, and add a waste allowance for excavation tolerance, overfill and shrinkage. Order the concrete in one go so the whole pour can be done in one operation without a construction joint. Several strips/points are calculated as separate volumes and added together. Use the «Concrete volume» calculator.

Lay the reinforcement according to the structural calculation and maintain the specified cover with spacers, so the reinforcement sits at the right height and is fully surrounded by concrete. Cover, amount of reinforcement and placement are design conditions — look them up, do not guess them.

Place the concrete, compact it (poker vibrator or tapping) so air pockets disappear and the concrete closes tightly around reinforcement and formwork, and screed the surface to the required level. Good compaction is essential for both strength and durability.

Protect the fresh concrete against drying out too quickly, sun, rain and frost during curing — e.g. by covering or watering. Concrete that dries too quickly or freezes early does not reach its strength. Only strike the formwork when the concrete has sufficient strength according to the project's instructions.