Step 1: Make a bigger crack

OK, it might seem counterintuitive to make the cracks bigger, but it's easier to fill a bigger crack. Use the coal chisel to scrape the crack until it is bigger, deeper and wider. Blow any dust away from the crack. Use the paint brush dipped in water to pick up any last dust in the crack.

Step 2: Fill the crack

Use the trowel to work some render firmly into the crack. Smooth the render with the back of the trowel until it is even with the surrounding wall. Wait about half an hour until the render is almost dry to the touch. Rub the rendered area with the sponge, which will make the edges of the render smooth with the wall. Tip: Use render that is nine parts soft sand, two parts lime and one part cement. The lime will give the cement some pliability, allowing it to expand and contract.