Who This Checklist Is For (And When to Use It)
If you're specifying silicone products for a production line, a maintenance project, or a new product assembly, you've probably realized that 'silicone' covers a lot of ground. Dow Corning makes hundreds of products—sealants, greases, fluids, compounds—and picking the wrong one can cost you more than just the price of a tube.
I'm a quality compliance manager at a medium-sized industrial parts manufacturer. I review roughly 200+ unique items per year for spec compliance. Over the last four years, I've rejected about 12% of first deliveries due to material mismatches. Most of those came down to one thing: someone chose a silicone product based on name recognition rather than specific performance requirements. Let's fix that.
This is a 4-step checklist. Use it when you're choosing a Dow Corning product for the first time, or when you're considering a substitution.
Step 1: Classify the Physical Form
Silicone products come in forms that behave completely differently. Trying to use a grease where you need an adhesive is like trying to paint with butter. It won't just fail—it'll make a mess. Separate your requirement into one of these categories:
- Sealant/Caulk - Thick, paste-like, cures to a rubber. For gaps, joints, seams. E.g., Dow Corning 791 (building sealant), 732 (multi-purpose).
- Grease/Compound - Semi-fluid, doesn't cure. For lubrication, thermal transfer. E.g., Molykote 111 (valve grease), 340 (heat sink compound).
- Adhesive - Bonds parts together. Often cures to a clear or translucent elastomer. E.g., 3145 RTV (adhesive/sealant for electronics).
- Fluid/Oil - Low viscosity. For damping, hydraulic systems, or release agents.
- Dispersion - Solid silicone particles in a liquid carrier. Used for coatings or impregnation. E.g., medical dispersions for catheter coatings.
Here's the mistake I see beginners make: they treat 'silicone grease' as a single category. It's not. Molykote 111 is a high-viscosity grease for food-grade valves. The 340 compound is for heat transfer. They're both greases. They don't do the same job.
If you're still thinking 'silicone is silicone,' stop there. Pick the form first.
Step 2: Get VERY Specific on the Cure Mechanism (A Step Most Skip)
This is where most spec errors happen. Not all silicone cures the same way. Pick the wrong cure type, and your part either takes days to set or corrodes the electronics inside it.
Acetoxy cure (vinegar smell) - Fast cure, great adhesion, but releases acetic acid. Will corrode copper, brass, and sensitive electronics. Use for general building joints, glass, ceramics. Do not use on electrical connections.
Neutral cure (alkoxy or oxime) - No corrosive byproducts. Slower cure than acetoxy. Safe for electronics. This is what you need for any application near sensitive metals or electrical components.
Condensation cure (RTV) - Needs moisture from the air to cure. Thicker sections take longer (or won't cure at all if sealed). Use for sealants and gaskets. Limit section thickness to about 1/4 inch for reliable cure.
Addition cure - Heat-activated. Fast, predictable, no byproducts. Used in precision molds (like those heart molds people use for crafts) and medical devices. If you need FDA-grade silicone for a medical application, you're almost certainly looking at an addition-cure system.
I ran a blind test with our engineering team three years ago: same physical gap, one sealed with an acetoxy-cure sealant and a metal enclosure nearby vs. a neutral-cure sealant. 70% of the team identified the acetoxy batch as 'corroded' within two weeks without knowing what we'd used. The cost difference was about $0.15 per foot. On a 50,000-unit order, that's $7,500 for measurably better protection.
It's tempting to think 'any cure will do.' The corrosion potential ignores that. Period.
Step 3: Match Temperature and Chemical Exposure
Dow Corning has general-purpose silicones, and they have specialty ones. General-purpose (like 732) handles -60°C to 200°C continuous, with peaks to 230°C. That covers most HVAC and building applications. But if you're putting it next to a heat sink (like with 340 heat sink compound), you need to check the upper limit.
Here's the nuance that gets missed: chemical resistance. Silicone is great against water, steam, and many oils. It's terrible against concentrated acids, alkalis, and aromatic hydrocarbons (like gasoline, toluene). If you're sealing a flange in a food processing plant that gets cleaned with a caustic solution, general-purpose silicone will degrade. You need a grade rated for caustic washdowns, or you need to use a different material (like PTFE, but that's another discussion).
Checklist for this step:
- What is the continuous temperature range? (Not just the peak.)
- Does the sealant contact any chemicals? (Food acids? Cleaning agents? Oils? Solvents?)
- Is immersion likely? (Silicone absorbs some fluids, which can cause swelling and loss of adhesion.)
The 'always pick the high-temp option' advice ignores the fact that higher temperature ratings often come with reduced flexibility or poorer adhesion. Use the spec that matches your actual operating conditions, not a 'more is better' approach.
Step 4: Verify Cure Time and Application Conditions
This is the practical bottleneck. You've chosen the right product. Now can you apply it?
Will it cure in your environment? RTV silicone needs moisture. If the relative humidity is below 20%, cure slows way down. If it's winter in a heated warehouse with low humidity, a standard silicone may take 3-5 days to fully cure instead of 24 hours.
How thick is the joint? RTV silicones cure from the surface inward. A 1-inch thick seal may never fully cure in the center. For thick sections, look at two-part addition-cure products or specialty formulations from Dow Corning's high-performance compounds range.
Do you have time to let it cure? If you're doing production-line assembly with a 30-minute cycle time, standard RTV won't work. You need a fast-cure grade (some acetoxy options tack in 5 minutes) or a heat-cure addition system. If you're doing a weekend maintenance job on a pipe joint, 24-hour cure is fine.
Also: does the substrate need primer? Many Dow Corning sealants stick well to glass and aluminum without primer. Porous surfaces (concrete, wood) and plastics (especially polyethylene, polypropylene, and PTFE) may need a primer or surface treatment. The data sheet is not optional reading here.
I should add that we didn't have a formal verification process for cure conditions at first. Cost us when a rush job of 8,000 units was assembled with a standard 732 sealant in a dry, cold warehouse. The seal never properly adhered. We had to redo the entire assembly—materials alone were a $22,000 hit, not counting the labor and the delayed launch.
Common Mistakes and What to Watch For
The 'Silicone Grade Bloat' Error: Specifying a premium grade (like a medical-grade dispersion) when a high-quality industrial grade would work. The dispersion is great for catheters. For your industrial gasket application, it's overkill and three times the cost.
The 'One Product Fits All' Assumption: We had a vendor propose Dow Corning 791 for a structural glass bonding application. 791 is an excellent building sealant for expansion joints. It's not designed for structural adhesive loads. That would have been a clear spec mismatch.
The 'It's All Silicone' Mindset: Butyl rubber gloves vs nitrile gloves is a classic example outside our space—same material misunderstanding: one offers chemical resistance, the other doesn't. Same with silicones. Just because Dow Corning makes something doesn't mean every product is right for every job.
The bottom line? Use this checklist. Classify the form. Get the cure mechanism right. Match the environment. Then verify you can actually apply it within your constraints. Do that, and you'll reject a lot fewer deliveries.