Spraying putty and 2K primer is part of the car paint repair process. During which, many touch-up defects will be encountered, and one of the common is the cracking of the putty filling area or the primer layer, which leads to the cracking of the topcoat layer. Why does this happen?
1. The putty layer or 2K primer layer is too thick, and the drying time between each layer is not enough, so the surface of the putty layer or 2K primer of automotive refinish layer is dry but the bottom layer is soft, resulting in cracking of those areas. During the time of putty scraping or primer spraying, thin layers should be applied multiple times, and sufficient drying time should be allowed according to climatic conditions.
2. The transition area between the putty/2k primer layer and the old auto paint layer is not sufficiently treated, so that the putty coating is not tightly bonded and cracked. It is recommended to use 600# sandpaper to avoid bringing solvent into the deep layer.
3. The 2K hardener is not stirred thoroughly before usage.
4. Unsuitable thinner and hardener is used with the primer, which makes the primer layer not easy to dry or crack due to excessive shrinkage.
5. The putty is diluted, which means, a solvent-based thinner is added to the putty to make it thinner, which leads to cracking after being scraped and applied to the car. Putty generally cannot be diluted with solvent-based thinners.
If cracking has been encountered, the cracked area will need to be sanded thoroughly, re-scrape putty and spray 2K primer and topcoat, allowing adequate drying time between coats.
