When it comes to weatherproofing the joints between tilt-up or other precast concrete panels, the last thing any contractor wants is sealant adhesive failure. What is wanting is lasting protection against the weather and freedom from callbacks. How can these goals be achieved? There's a difference in concrete form release agents. All are helpful in removing dense panels from forms but some are quite detrimental to sealants. For instance, agents containing wax, oil, or silicon are harmful. They leave a surface film that impairs the adhesion of the sealant to the joint surface and usually causes the sealant to lose its grip in a matter of weeks. To prevent this problem an agent should be used that will be absorbed by the concrete during the curing process. It is a good idea still to check panel joint surfaces before sealing the joints. Any release agents found must be removed. The only sure method is light sandblasting. Precast panel joints should always be checked for laitance, a lightly bonded dusty or powdery surface. Though not always visible, it ranks high on the list of sealant saboteurs. A simple test is to apply masking tape to the panel joint surface before sealing the joint. If laitance is present it will show up on the tape when the tape is stripped off. For either regular or exposed aggregate panels, any laitance should be removed by wire-brushing, high pressure water spray, or light grinding.