Sealants now available and present knowledge of joint sealing criteria are adequate to provide successful joint sealant installations at least 90% of the time. Use of an appropriate type of sealant and proper sealant installation, however, are not a guarantee of successful performance. The location and design of the joint itself may be to blame if sealing problems develop. Also, the shape of the joint and the amount and type of movement that occur at the joint will affect sealant behavior. The best way to ensure that sealing efforts will pay off is to combine the right type of sealant with the appropriate joint detail for the application, then properly design, specify, install, and maintain the joint sealant system. Joint sealants fall into two categories: field-molded and preformed. Field-molded sealants are applied in liquid or semi-liquid form and take on their required shape from the mold provided at the joint opening. They usually cycle between compression and tension and change their shape without changing their volume. Preformed sealants are preshaped in relatively solid form, usually are in compression, and change their shape as their width changes.