ASI 388 Electronic Grade RTV Silicone, Clear, 10.2 oz Cartridge

This ASI 388 10.2 oz cartridge is the production size of ASI 388 Electronic Grade RTV Silicone: a clear, one-part, neutral-cure (oxime) silicone that cures in room air to a tough, flexible rubber. A cartridge makes sense when bead after bead has to go down with a caulking gun, for example on a run of enclosures, panels or cable entries, rather than being squeezed from a small tube.

Key features

• Non-corrosive, electronic-grade neutral cure (per ASI); no acetic acid released while curing
• UL Recognized (File No. E209770), meets MIL 46106B Type 1, VOC compliant at 21 g/L
• Electrical data: 500 V/mil dielectric strength, dielectric constant 3 and dissipation factor 5 × 10⁻³ at 50 Hz
• Gun-grade, non-slump paste that skins in about 20 minutes at 70°F and 50% RH
• Cured rubber: 30 Shore A, 300 psi tensile strength, 600% elongation; -70°F to 400°F service, 450°F intermittent

Where to use it

ASI’s application list centers on electronics and telecom: sealing lead-wire entries, waterproofing and sealing electronic assemblies, circuit board protection, component mounting, encapsulating, and coaxial cable connectors. ASI also lists engine components and general industrial work. The cartridge suits builders sealing many enclosure lids or cable entries, shops assembling control boxes or outdoor sensor housings, and field crews weatherproofing coax connections across a job.

How to use

1. Clean parts with 100% isopropyl alcohol or acetone, as ASI recommends, and let them dry; avoid petroleum-based solvents. Work on de-energized equipment.
2. Load the cartridge into a standard caulking gun and cut the nozzle to the bead size you need.
3. Apply within ASI’s application range of -35°F to 150°F and tool within about 20 minutes, before a skin forms.
4. Allow about 24 hours per 1/8″ bead. Deep or confined beads cure more slowly; warmth and humidity speed things up.
5. Run adhesion or strength checks on day 7, as ASI recommends.

Compatibility and cautions

ASI lists glass, most metals, aluminum, steel, most fiberglass, porous surfaces, vinyl, PVC, rubber, natural and synthetic fiber, most painted surfaces and some plastics. Its data sheet also warns that 388 can discolor copper around the applied or confined area, so trial it where copper appearance matters. The curing by-product is methyl ethyl ketoxime (MEKO); the SDS lists eye irritation, possible skin sensitization and suspected fertility effects, so use gloves, eye protection and good ventilation. Shelf life is 12 months from shipment at 70°F and 50% RH, so buy what you will use in that window. Label, TDS and SDS: technical documents.

Choosing between sizes and formulas

For occasional repairs or tight spots, the ASI 388 2.8 oz squeeze tube is easier to handle. If the job is a general seal with no electronics or sensitive metal involved, the acetoxy ASI 502 clear 10.2 oz cartridge skins faster (about 10 minutes) and is listed to NSF Standard 51 for incidental food contact. Keep 388 for electronics and for metals an acetoxy cure could corrode. Background reading: neutral-cure silicone guide and acetoxy silicone guide.