C.R. LAURENCE 999AW CRL White Dow Corning 999-A Silicone Building and Glazing Sealant. Dow Corning 999-A is a one-part acetic cure silicone sealant that cures in the presence of atmospheric moisture to produce a durable and flexible wet glazing and curtainwall seal. It is designed for conventional glazing of glass and plastic, curtainwall sealing, solar panels, and replacement glazing.. Part Numbers Variations: 999AW