Structural glass glazing is an aesthetically pleasing architectural feature, but the systems must transfer wind loads from the glass to the supporting structure while accommodating movement caused by temperature changes, building movement, and seismic activity. As a result, the assembly of a structural glass glazing system and the materials used to bond the panels are essential to their overall performance.
Our team reviews two popular structural silicone glazing (SSG) sealants: Tremco Proglaze® II and DOWSIL 983™. We compare their performance capabilities and specifications, as well as outline their ideal use cases, to help you determine which one is best for your application.
About Tremco Proglaze II
Tremco Proglaze II is a two-part, neutral-cure silicone sealant designed for structural glazing applications. It is a high-modulus sealant that cures into a tough, flexible rubber when properly mixed. The formula offers ±25% movement capability and a controlled cure time that can help reduce glazing and sealing production time.
The Tremco Proglaze II silicone sealant meets the following standards:
- ASTM C920, Type M, Grade NS, Class 25, Use NT, G, and A
- Federal Specification TT-S-00227E, Type II, Class A
Designed primarily for two-sided and four-sided structural glazing applications, the Proglaze II SSG is most commonly used for factory glazing and curtain wall production.
About DOWSIL 983
DOWSIL 983 is a dual-purpose, two-part structural silicone sealant used for structural glazing and weathersealing applications. It is a neutral-cure silicone that offers both high structural strength and watertight seals for long-term durability in outdoor conditions. It has a high movement capability of ±25%, offers primerless adhesion to many substrates, and has a low VOC formula.
The DOWSIL 983 silicone sealant is also marketed by Dow as:
- Meeting ASTM C719 Class 25 (G, A, O)
- Meeting ASTM C1184 Structural Glazing Specification
- A low embodied carbon DOWSIL™ Silicone
- Offering a project-specific DOW Carbon Neutrality Certificate on request
- Potentially contributing toward additional credits in green-building certification programs
DOWSIL 983 can bond aluminum, glass, metal, and other materials. It is most commonly used for curtain wall production or factory glazing.
Tremco Proglaze II Versus DOWSIL 983
While both can be used for structural glass glazing applications, they differ in performance. We outline the key similarities and differences between the Tremco Proglaze II and DOWSIL 983 sealants to help you determine which one is a better match for your application.
| Property | Tremco Proglaze II | DOWSIL 983 |
|---|---|---|
| Sealant type | Two-part structural silicone sealant | Two-part structural and weatherseal silicone sealant |
| Cure chemistry | Neutral cure | Neutral cure |
| Movement capability (ASTM C719) | ±25% | ±25% for weatherseal applications |
| Snap time | 30-60 minutes | 20-60 minutes |
| Shore A hardness (ASTM C661) | 40 to 45 | 35 to 45 |
| Tensile strength (ASTM D412) | 200 to 210 psi (1.37 to 1.44 MPa) | 300 psi (2.0 MPa) |
| Maximum elongation (ASTM D412) | 275% to 300% | 400% |
Choose Tremco Proglaze II when you need a high-modulus, non-sag silicone developed specifically for two-sided or four-sided structural glazing. It is well suited for dedicated structural glazing applications, including in-plant glazing and curtain wall production.
Choose DOWSIL 983 when you need one product for both structural glazing and weathersealing. DOWSIL 983 may also be the better choice when low VOC content, documented embodied-carbon claims, or sustainability is important.
Mixing, Dispensing, & Application
Whether you choose Tremco Proglaze II and DOWSIL 983, both sealants rely on proper mixing and application to live up to their expected performance capabilities. The wrong mix ratio, incomplete mixing, or improper surface preparation can lead to poor adhesion or bond failure.
Surface preparation for both materials will vary depending on the specific application. Both products can provide unprimed adhesion to common substrates used in glass glazing. A primer may be recommended for substrates with special surface characteristics. Both the Tremco Proglaze II and DOWSIL 983 technical datasheets emphasize that the structural joint design should be reviewed by a technical service specialist, and installation should generally follow their structural glazing guidelines.
Along with proper surface preparation, the Tremco Proglaze II and DOWSIL 983 two-component sealants require proper mixing before application to the substrate. The Tremco Proglaze II datasheet specifically says hand mixing or mechanical mixing is not acceptable.
Compatible dispensing systems are required, as they can provide precise and accurate metering and mixing of the materials. The HG Little Bear silicone dispensing system, for example, is designed specifically for field glazing applications. It is compact and pneumatically powered for ease of use at job sites. If you are looking for a factory-glazing system for higher-volume production, the HG 437 silicone dispensing system is a good option.
Choosing between the Tremco Proglaze II and DOWSIL 983 silicone sealants is only part of the equation. Accurate dispensing and application are equally important to ensure proper performance.
At Dispensing.com, we offer structural silicone glazing sealant dispensing systems designed to handle either of these materials efficiently and consistently. Contact our dispensing experts for help selecting the right equipment for your application or guidance on how to optimize your application process.
Dispensing.com is not affiliated with Dow or Tremco. DOWSIL™ is a trademark of The Dow Chemical Company or an affiliated company of Dow. Proglaze® II is a registered trademark of Tremco Incorporated.
