USE RESIN TO FIX KNOTS IS MUCH TOUGHER AND SMOOTHER

Resin is a natural or synthetic compound that begins in a highly viscous state and hardens with treatment. Typically, it is soluble in alcohol, but not in water. The compound is classified in a number of different ways, depending on its exact chemical composition and potential uses. It also has many applications, ranging from art to polymer production, and many consumers interact with products that contain it on a daily basis.

Natural resin comes from plants. It's much healthier than putty. A classic example is pine sap, which has the characteristic sharp odor of terpene compounds. As anyone who has interacted with pine sap knows, the substance is very viscous, but it hardens over time. A number of other plants produce resins, and they have been used by humans for thousands of years. 

We use resin to fix knots, because it's tougher and smoother than putty. Putty will fall off easily, but resin will not even you prize it.