Cracking is often experienced when using plant-based waxes. Cracks can appear on the surface or throughout the candle. Cracks can appear in different forms. Sometimes cracks occur as shallow localised cracks that form a rough circular shape on the surface of the candle. These cracks often appear above a cavity in the wax. Occasionally, radial cracks can form across the top of the candle, running from one edge to the other and normally passing through the wick area. Radial cracks can be deep, often running from the top to the bottom of the candle.

As the wax cools, it goes through different stages of crystallisation. During those phases the wax can contract and crystallise in different ways, causing cracks to occur. Cracking is a common problem in plant wax candle making, with rapeseed wax being more prone to radial cracks. Soy wax, while less likely to crack, tends to produce circular or radial cracks. If candles are allowed to cure in cool environments, they are more likely to crack.