Momentive RTV157 Processing Recommendations
Application and Cure Time Cycle
RTV157 and RTV159 sealants may be applied directly to clean or primed substrates. Where broad surfaces are to be mated, the sealant should be applied in a thin, less than 6mm (1/4 in.) diameter, bead or ribbon around the edge of the surface to be bonded.
The cure process begins with the formation of a skin on the exposed surface of the sealant and progresses inward through the material. At 25°C (77°F) and 50% relative humidity, RTV157 and RTV159 sealants will form a tack-free surface skin in about 30 to 60 minutes. Once the tack-free skin has begun to form, further
tooling of the adhesive sealant is not advisable.
As the adhesive sealant cures, acetic acid vapours are released from the sealant surface. The odour of acetic acid will completely disappear when curing is completed.
Because these adhesive sealants cure by reacting with atmospheric moisture, higher temperatures and humidity will accelerate the cure process lower temperatures and humidity will slow the cure rate. Exact cure time will depend on temperature, humidity, sample thickness and sealant configuration. Since
cure times increase with thickness, use of these adhesive sealants should be limited to section thicknesses of 6mm (1/4 in.) or less
Bond Strength Development
In addition to the effects of temperature and relative humidity, development of maximum bond strength will depend on joint configuration, degree of confinement, sealant thickness and substrate porosity. Normally, sufficient bond strength will develop in 12 to 24 hours to permit handling of parts. Minimum stress should be applied to the bonded joint until full adhesive strength is developed, generally considered to be 7 days at 73°F / 50% RH. Eventually, the adhesive strength of the bond will exceed the cohesive strength of the silicone rubber adhesive sealant itself. Always allow maximum cure time available for best results.