Question 1: Same silicone rubber — what does "addition" vs. "condensation" actually change?
Answer: One sentence: addition-cure crosslinks vinyl + Si–H with platinum and gives off nothing; condensation-cure joins Si–OH with an alkoxime/alkoxysilane crosslinker and releases a small molecule (alcohol, oxime, acetic acid…).
That single difference cascades through everything else: addition systems show essentially no by-product, linear shrinkage <0.1%, deep cure through any thickness, but cost more and are vulnerable to catalyst poisoning; condensation systems are cheaper, stick to many substrates naturally, cure at room temperature using air moisture (RTV-1) or tin/bismuth catalysts (RTV-2), yet release volatiles that slow thick-section cure, drop initial dielectric strength, and cause "reversion" when sealed parts are reheated. Selection rule: precision potting, optics, thick sections → addition; moldmaking, sealing, budget-driven jobs → condensation.
Question 2: Where exactly do they differ in practice? Can one replace the other?
Answer: Let's look scenario by scenario (based on measured parameters of commercially available grades):
Conclusion: They are complementary, not interchangeable. For LED/optical potting, power supplies, solar junction boxes, deep-pour encapsulation, and food/medical-grade silicones, addition-cure wins outright — no shrinkage, no reversion, no corrosive by-products. For mold making, construction sealants, large-area glazing, and cost-sensitive gaskets, condensation-cure remains the practical choice because it self-adheres, tolerates dirty shop conditions, and costs less per kilogram. Three caveats before switching: ① addition systems demand clean tooling — gloves, molds, and mixer parts contaminated with amine/sulfur/tin chemistry will leave uncured spots; ② condensation acetoxy grades corrode copper and sensitive electronics — pick oxime or alkoxy types there; ③ if a condensation part will see sealed high heat, insist on stepped post-cure to vent volatiles. Verify all substitutions with sample testing on your actual process.
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