Applying sand and cement render to lightweight blocks

The first coat (or the scratch coat) is mixed at 5-1. This means 3 sharp sand, 2 soft sand and 1 cement. This coat is applied between 5-6mm. The render is pressed firmly into the wall to ensure that every inch is covered. Once the first coat has been applied, it is then scratched by a scratch comb. This gives the second a good key. If the first coat is dry before coming onto the second coat, then it is wet down in order to slow the absorption rate. The second coat is also mixed at 5-1 but this time it is 2 sharp sand, 3 soft sand and 1 cement. This coat is applied at 10mm.

Once the second coat has been applied, it is gone over using a plasterers darby to remove any bumps and creating a smooth surface. By doing this, you also ensure a uniform thickness.
To complete the rendering, a float is used to ensure that the wall is completely flat and a brush is used to tidy up any surrounding surfaces.

If the application is not done correctly the render will most likely crack due to the high suction level of the block. The best way to avoid this is to use base coats that are suitable for light work block.