Shore hardness is a measurement of a cured coating's resistance to indentation, tested with a handheld durometer and expressed on a Shore A or Shore D scale depending on how rigid the material is.
Understanding Shore Hardness in Coatings
Shore hardness is measured with a spring-loaded device called a durometer, which is pressed against the cured coating and gives a reading based on how far its indenter penetrates the surface. Softer, more flexible materials like polyurea membranes are tested on the Shore A scale, while harder, more rigid coatings like cured epoxy and polyaspartic topcoats are typically tested on the Shore D scale.
What Affects a Coating’s Shore Hardness?
Resin chemistry is the main factor, since epoxies and polyaspartics naturally cure harder than flexible polyureas. Full cure time also plays a role, since hardness readings taken before a coating fully cures will be lower than its final value. Additives like plasticizers, sometimes used to increase flexibility, will lower the hardness reading in exchange for better impact and crack resistance.
Shore Hardness vs. Coefficient of Friction
Shore hardness measures how resistant a coating is to indentation and wear, while coefficient of friction measures how slip resistant its surface is. A coating can be very hard and still be slippery, or softer and still provide good traction, so specifiers typically look at both properties together rather than assuming one predicts the other.
Practical Tips for Using Shore Hardness Ratings
Compare hardness values only within the same scale, since a Shore A reading and a Shore D reading are not directly comparable. Take readings after the coating has reached its full cure time listed on the technical data sheet, not right after the recoat window closes. Match the hardness to the application, since a very hard coating resists gouging in a warehouse, while a slightly softer, more flexible coating can better handle substrate movement or impact in other settings.
Also Called
Durometer Hardness, Shore Durometer Reading
