Putty Hardeners

2K (two-component) polyester putty must be used with a compatible hardener to achieve full cure, strength and durability. BPO (benzoyl peroxide) hardeners initiate the chemical reaction that hardens the putty; without the correct hardener and cure conditions the repair will remain soft and weak. For best results mix putty and hardener on a mixing board, use a Japanese putty knife for application, and follow the manufacturer’s specified pot and cure times. Typical mixing ratio for BPO hardeners is 1–4% by weight of the putty—follow the product instructions precisely. Proper mixing, controlled temperature and correct working times are essential for adhesion, sanding performance and long-term durability. Safety: always wear nitrile gloves, safety goggles and appropriate respiratory protection in a well-ventilated area. BPO hardeners are commonly a greyish or white paste/gel; add them carefully and mix evenly into putty or gelcoat before application to ensure a reliable repair.