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Why is the putty or primer cracking?

Feb 22, 2023

Why is the putty or primer cracking?


Spraying a putty primer is part of the automotive paint refinishing process. During this process, many touch-up defects will be encountered, and one of the common ones 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 mid-coat primer layer is too thick, and the drying time between each layer is not enough, so the surface of the putty layer or mid-coat primer layer is dry and the bottom layer is soft, resulting in cracking of the putty layer or mid-coat primer layer. In putty scraping or primer spraying, thin layers should be applied multiple times, and sufficient drying time should be allowed according to climatic conditions.


2. Insufficient treatment of the putty or the transition area between the primer layer and the old paint layer, which makes the putty coating not tightly bonded and cracked. It is recommended to use 600 sandpaper to avoid bringing solvent into the deep scratch layer of the lower layer .


3. The curing agent is not evenly stirred before use, and the curing agent and the main agent should be stirred evenly before use.


4. Unsuitable thinner is used in the primer, which makes the primer layer not easy to dry or crack due to excessive shrinkage.


5. The putty is diluted, that is, a solvent-based thinner is added to the putty to make the putty thinner, resulting in 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-scraped putty and sprayed with primer and topcoat, taking care to allow adequate drying time between coats.





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