Will Not Dry or Harden, Always Adjustable: Unlike epoxy and traditional sealants, E/Fusing 900 remains in a putty-like state, allowing you to reposition, reshape, or remove it whenever needed. E/FUSING 900 is a non-hardening multi-purpose gap sealant putty for filling voids, cracks, and seams where water, air, or wildlife intrusion is a concern.