Dow Corning 995 vs 785 Silicone Sealant: An Honest FAQ from a Procurement Guy

I'm a procurement lead who's been handling silicone and elastomer orders for 8 years. In that time, I've personally made and documented 14 significant mistakes—totaling roughly $30,000 in wasted budget. Now I maintain my team's pre-order checklist so other people don't repeat my errors. These are the questions I actually get asked, plus the one I wish someone had asked me.

What's the real difference between Dow Corning 995 silicone structural sealant and Dow Corning 785 silicone sealant?

Dow Corning 995 is a structural silicone sealant designed for structural glazing—load-bearing glass joints, curtain wall panels, that kind of thing. Dow Corning 785 (also called the 'neutral cure' sealant) is a general-purpose, non-structural sealant. Back in 2019, I used 785 on a curtain wall mockup because it was cheaper. Looked perfect for two weeks. Then the shear test failed. That mistake cost $5,200 in redo plus a 10-day delay. Or rather, $6,100 if you count the overnight shipping. Quick rule: 995 for structural, 785 for everyday sealing.

Can I substitute Dow Corning 785 for structural applications?

No. I'm not being dramatic; I'm being specific. 785 handles weather, movement, and standard joint sealing well. But it is not specified for structural glazing or load-bearing adhesion. If the spec says 'structural sealant' or references ASTM performance requirements, 785 is not your sealant.

I learned this by ignoring a senior engineer's warning in 2019. The sealant failed adhesion pull testing on day three. Why does this matter? Because the cost isn't just material—it's rework, retesting, schedule impact, and losing the team's trust. Check the project spec first. If you're unsure, ask for the technical data sheet.

What should I look for if I'm searching for 'silicone buttocks' or body-contact silicone materials?

That search term sounds odd, but I get it from manufacturers working on soft-touch medical and personal care products. If you're buying silicone for body-contact parts, don't stop at durometer and color. You need biocompatibility documentation, not just a nice feel.

Per FTC guidelines (ftc.gov), claims like 'medical-grade' or 'body-safe' need evidence to back them up. And in my experience, silicone vs TPE is not a clear winner. Silicone offers heat resistance and a distinctive feel; TPE can be easier to process and more affordable. I've sourced both. The right choice depends on your manufacturing process and regulatory requirements. What was best practice in 2020 may not apply in 2025.

How do I evaluate thermoplastic suppliers when I also need silicone parts?

I've ordered from 11 thermoplastic suppliers, and the biggest mistake early on was comparing only price per kilogram. The real metric is total cost: price per part, tooling lead time, quality consistency, and how they handle changes mid-order.

I went back and forth between a cheaper new supplier and the incumbent for two weeks. The new one quoted 18% less. I switched on a 3,000-piece order, and every single batch had inconsistent hardness readings. We caught it before shipping—lucky—but QC hours ate the savings. Fundamentals haven't changed: price, quality, delivery. But execution has. Good suppliers now share process data, not just samples. Ask for a process capability report and a sampling plan.

How do I clean PVC pipe before applying silicone sealant?

Most people skip this step. I did too, and my first attempt at sealing a PVC drainage joint with silicone failed within a month. The secret is not to use common degreasers or citrus cleaners—they leave a residue that kills adhesion.

Use isopropyl alcohol (90% or higher) on a lint-free cloth, wipe the PVC surface, let it dry completely, then apply. It works because PVC often has mold-release residue from manufacturing. Water won't remove that. Which leads me to the question people don't think to ask:

Why would a Dow Corning sealant cure fine but peel off later?

Usually surface prep or expired material. In late 2023, I bought a batch of 995 that looked normal but came out of a hot warehouse. Shelf life is typically 12 months from the manufacture date, but heat shortens that. It cured on the surface; adhesion was weak underneath.

The manufacturer publishes storage guidelines, and I ignored them. Now I check every lot number and run a small bead on the actual substrate before big jobs. That habit has caught 47 potential failures in 18 months. My experience is based on mid-size projects, so your volumes might differ—but the test costs a day, and the failure costs a lot more.