ASI 335 neutral cure silicone can be used as a durable, general-purpose sealant/adhesive in a wide range of industrial applications. Unprimed adhesion to a wide range of substrates is available with the use of ASI 335. For example, ASI 335 neutral cure silicone adheres to unprimed chrome and stainless steel, which other high modulus silicone sealants would require to be primed. As a formed-in-place gasket, ASI 335 exhibits low swell, low compression set and good oil resistance. These characteristics impart an unusual balance of properties to ASI 335 to prevent leakage in harsh environments such as engines, transmissions, water pumps, rear axles and oil pans. ASI 335 is not recommended to be used in cylinder heads, exhaust manifolds or in contact with fuels.
ASI 335 neutral cure silicone is ready to use and requires no mixing or additives. The cure mechanism begins as soon as the sealant comes in contact with the air. At conditions of 25°C (77°F) and 50% relative humidity, the sealant will skin in 10-20 minutes and cure in 24 hours (1/8″ bead), with full cure strength in 7 days. Higher humidity accelerates cure. Tooling should be done before skinning takes place. In applications where partial or total confinement of sealant is prevalent, the time required for proper cure is generally lengthened by the degree of confinement.
Provided that all bonding surfaces are clean and dry, ASI 335 neutral cure silicone has excellent unprimed adhesion to most substrates. If there is any doubt about contamination, surfaces should be solvent wiped with oil-free solvents, such as xylol, toluol, naphtha or non-flammable chlorinated solvents. Do not solvent-wipe with oil-based solvents such as Varsol.
Priming for ASI 335 neutral cure silicone is normally not required for application to most substrates. Unprimed adhesion can be readily tested by applying a small trial bead and allowing 7 days for maximum adhesion to occur. ASI 335 has excellent unprimed adhesion to many substrates as shown in the adhesion chart.