Bondo All-Purpose White Cream Hardener is specially designed to be used with Bondo All-Purpose Putty. When the filler and hardener are mixed, a chemical reaction occurs to deliver long-lasting home repairs and professional looking results.Bondo All-Purpose White Cream Hardener mixes with 2-part fillers, putties and glazes to create high-quality, long-lasting repairs. When filler and hardener are mixed, a chemical reaction occurs to create a mixture that will deliver a strong, lasting repair. Our hardener is smooth and easy to mix with fillers, putties and glazes.