Sika 3/4 In. Backer Rod is used to partially fill deep expansion joints and cracks before the application of your sealant. It helps prevent 3-sided adhesion while allowing you to control the depth of the sealant. Backer Rod is used to partially fill deep cracks or joints before applying sealant Helps improve durability and stability of your joint or crack application Assists in a proper joint design For vertical and horizontal applications Compressible and non-absorbent