Automobile dashboards are composed of several layers of plastics. The top layer in older automobile dashboards is usually made from polyvinyl chloride, commonly called PVC. PVC can crack after a few years of exposure to sunlight and heat if not properly maintained and protected. The dashboards of older cars, especially classics, tend to become brittle and crack after many years of exposure to the sun.

1. Ultraviolet Light

The most common cause of dashboard cracks is exposure to ultraviolet light. Ultraviolet light is harmful to the chemical components of plastics such as PVC. Over time, ultraviolet light can evaporate oils and break down the plastic molecules. If regularly exposed to ultraviolet light, the dashboard plastic will become dry and crack.

2. Heat

Extended exposure to heat, such as parking the car in the open and exposing the dash to sunlight through the windshield, can break down the chemical molecules in the dashboard. The interior of a car can exceed 100 F on a sunny day after about one hour of exposure. Dashboards that have a dry, dusty or powdery appearance have been damaged by heat and ultraviolet light.

3. Repairs

Small cracks can be repaired. The entire dashboard must be replaced if the cracks are deep and long. The dashboard should be replaced if the cracks have a spider web appearance. Filling the crack with silicon or using a dashboard crack repair kit, available at most auto parts stores, is a temporary fix. The crack will probably reappear in a couple of years, especially if the dashboard is exposed to heat and sunlight.

4. Prevention

Prevent cracks in a dashboard by protecting it from ultraviolet light and extreme heat. Park the car inside a garage or in a shady location. Use a windshield screen or a car cover year-round to block sunlight and prevent damage. Apply a moisturizing treatment to the dashboard to prevent the PVC from drying out. Select a treatment that contains a sunscreen to block ultraviolet light.