Typically, the job of a sealant is to fill gaps that are exposed to the elements and experience minor to moderate movement. Adhesives are different in that they work best in confined, unexposed spaces.
Occasionally, that doesn’t stop someone from trying to force a sealant to behave like an adhesive. Silicone is the most common material for this “misuse.”
… Or is it a misuse? If you’ve ever asked, “Can I use silicone sealant as an adhesive?” you’re in the right spot.
Your experience may differ, depending on the application. But, generally speaking?
Yes, you can use certain silicones as a construction adhesive.
Now, is silicone sealant a good adhesive? That depends on the product as well as the substrate(s). It's important to understand the differences and characteristics of sealants vs. dedicated adhesive products.
First, let’s define sealants. These gap-closers come in several material options; each has different surface compatibility and performance traits (like adhesion). One of those options is silicone, a rubber-like polymer made of siloxane. It’s widely hailed as the best construction sealant, although in certain job conditionss polyurethane may work better.
Now, on to adhesives. These construction products bond a component to another surface. They come in many forms, including:
|
Adhesive |
Example Use Case |
|
Tape |
Bond and seal walls, windows, & doors |
|
Glue |
Support screwed-in wood assemblies |
|
Mirror Mastic |
Standalone solution for hanging bathroom mirrors |
|
Epoxy |
Bonding concrete pieces, drilling holes, load bearing |
|
As primer for a sheet membrane |
Adhesives can be rigid and durable, too. Structural adhesives feature a special formula for bonding applications, providing superior shear strength vs. general-purpose sealants.
Do you know someone who uses the terms “silicone sealant” and “silicone adhesive” interchangeably? They’re saying it a bit wrong.
Silicone adhesives don’t technically exist. If there’s a silicone product out there that’s adhesive, it’s still a sealant first (by name, at least).
Silicone sealant comes in the package in a paste-like consistency. Its flexible nature can accommodate movement without breaking. Sealants also include a structural line of products, which have higher:
As we mentioned, structural sealants can also be quite … adhesive. That’s where the confusion comes in. That doesn’t mean all sealants work as adhesives or as structural elements. Learn the product systems before you buy or use them.
The ability of a sealant to create a proper bond depends on the product composition and the working surface.
The best silicone adhesive sealants kill two birds with one stone, bridging the gap between waterproofing and structural products.
Silicone + adhesion might sound like an unbeatable dream team, but you should stick to traditional construction adhesives in many situations:
Only certain silicone products are acceptable as an adhesive solution. There are a couple of important material categories you should get to know:
Hybrid silicone is an answer for large-scale construction needs.
Made of silicone and polyurethane, a hybrid sealant combines the benefits of both worlds. The addition of polyurethane strengthens the sealant, forming a nearly unbreakable bond with the surface.
Benefits over standalone silicone and polyurethane products include:
This product specializes in helping engineer a strong infrastructure for buildings and bridges. They're ideal for any area where you want a durable, flexible seal, including:
This product's specialty is waterproofing on a smaller scale. Neutral cure products actually need moisture to cure, unlike other sealants that require chemical curing.
Because they don't release acetic acid, neutral cure silicone products are also noncorrosive.
From an adhesion standpoint, a neutral silicone sealant comes with plenty of perks:
Other benefits of neutral silicone sealant include its ability to easily cure around water surfaces. You'll never have to worry about it creating yellow stains, cracks, mold, or mildew.
Thanks to these qualities, neutral silicone is popular in many applications that need corrosion protection:
These aren’t the types of material you buy at Home Depot or Lowe’s for $7. Structural, adhesive silicone is a highly engineered product.
Structural silicone sealants have earned popularity in a variety of assembly, installation, and repair jobs. These types of sealants can add considerable design freedom to commercial buildings. Architects especially value the strength they bring to complex glass structures.
Structural silicone glazing is the technique of attaching glass to a metal frame using highly engineered and adhesive sealants. This allows architects to create glass-heavy structures with minimal obstruction.
The “structural” part is notable, as the glass panels actually bear part of the structure's weight. The process also results in a cleaner look vs. traditional metal retainers and trim.
If you pick a silicone product suited for mixed-material bonding, the possibilities are nearly endless for:
Certain expansion joint types (i.e. seismic-rated) also make use of silicone sealant. Expansion joints sometimes come with fuel- and traffic-resistant silicone, others with standard. The flexible, elastomeric nature of silicone allows it to effectively adhere to surfaces, even during expansion joint movement. The silicone is merely there to connect the factory-applied and cured silicone to either substrate.
Situational uses include:
Quality and compatibility make up half of the winning formula. The rest depends on actually installing the sealant properly.
|
Surface Prep |
Application |
Curing |
|
|
Before |
May need to abrade or roughen certain surfaces for applicability |
Get applicators that can handle structural sealants' high viscosity |
Watch the weather – humidity & low temps can slow drying |
|
During |
Remove debris & chemicals using manufacturer-rec'd cleaner for the substrate |
Apply steady, consistent pressure for proper bead size |
Expose sealed area to airflow (especially for thick beads & enclosed joints) |
|
After |
Wait for surface to dry before continuing |
“Tool” sealant immediately to improve surface contact, reduce air pockets |
Don’t subject joint to traffic yet – full bonding can take 10-14 days |
As always, check the manufacturer’s guidelines or ask your distributor about best practices for specific surfaces and conditions. And make sure your sealant and the working surface make a compatible team.
“Can I use silicone sealant as an adhesive?” Yes, you can, even in commercial construction. Just keep a few big asterisks in mind:
*Only use silicone specifically marked for structural use.
**Verify its compatibility with the substrate by consulting the manufacturer's guidelines.
There are more construction sealant and adhesive varieties than is possible to cover in one shot. For a more specific look at what’s out there, see our manufacturer list: