Specialty Sealants & Caulks

Q: What does ASTM C920 Class 25 actually mean?

Class 25 is the movement capability rating. The sealant can accommodate a joint that expands or contracts by ±25% of its original width without failing. A Class 25 sealant in a 1/2-inch joint handles ±1/8 inch of movement. For most vertical building joints, Class 25 is the minimum; curtain wall joints and large expansion joints typically need Class 50 or higher. The joint sealant selection guide covers the full Type/Grade/Class/Use decoder.

Q: Silicone, polyurethane, or hybrid: which sealant should I use?

Silicone for long-term weather exposure on glass, metal, and sanitary surfaces when paintability doesn't matter. Polyurethane for concrete, masonry, and horizontal traffic-bearing joints where you need to paint over the sealant. Hybrid STPE (sometimes called MS polymer) when you want silicone's weather resistance with polyurethane's paintability. The sealant and caulking selection guide has a chemistry-by-application matrix if you want to dig deeper.

Q: Can I paint over silicone sealant?

Most pure silicones cannot be painted. Paint beads up or peels off. A few silicone-hybrid products are labeled as paintable, but read the datasheet carefully. If the joint will be painted, use a polyurethane or hybrid STPE sealant instead.

Q: Which sealant is right for food-processing equipment?

Look for NSF/ANSI 51 certification for incidental food contact. Food-grade silicone is the most common choice because of its temperature resistance and long service life. Avoid general-purpose silicones with mildewcides or plasticizers in food areas. The food-processing sealants guide covers certification details and approved product categories.

34 products in this collection ↓

Industrial and specialty sealants for commercial construction, firestop penetrations, structural glazing, high-temperature service, and food-processing equipment. These are high-performance formulations defined by joint movement capability, temperature resistance, chemical resistance, and compliance with industry standards, not the everyday caulks you would find at a hardware store. For chemistry selection, joint design, and application guidance, the sealant and caulking selection guide is the starting point. To convert joint dimensions into cartridges, sausages, or pails, use the sealant yield calculator.

ASTM C920 Class 25: the industrial joint-sealant benchmark

For building joints, ASTM C920 is the baseline for elastomeric joint sealants. Class 25 formulations accommodate ±25% joint movement, the minimum grade for most commercial joints. Class 50 and Class 100/50 handle larger movements common in curtain walls and large expansion joints. C920 sealants carry a Type/Grade/Class/Use designation, and the joint sealant selection guide walks through decoding a spec string into a product pick.

Chemistry comparison

Chemistry	Exposure	Paintable	Movement	Typical use
Silicone	Excellent (20+ yr)	No (most)	±25% to ±50%	Curtain walls, glazing, sanitary joints
Polyurethane	Good (10 to 20 yr)	Yes	±25%	Traffic decks, sidewalks, masonry
Hybrid STPE / MS polymer	Very good	Yes	±25% to ±35%	Low-VOC occupied buildings, multi-substrate
Intumescent firestop	Indoor only	Yes (most)	Per UL listing	Rated wall/floor penetrations
High-temp silicone	500°F+ continuous	No	Limited	Furnace doors, flue pipe, exhaust

By application

Commercial construction: C920 Class 25 for vertical joints, Class 50 for expansion joints, and UL-listed firestop systems tested to ASTM E814 for rated wall and floor penetrations. For firestop selection, see the firestop product selection guide; for electrical boxes in rated walls, the firestop putty pads guide. For data centers, colocation, and mission-critical facilities, start with the NFPA 75 firestop guide for data centers or the broader firestop compliance hub for mission-critical facilities.

Manufacturing and industrial: high-temperature silicone for furnaces and exhaust, chemical-resistant polymers for process piping, and NSF 51 certified sealants for food and beverage lines. See the high-temperature sealant guide and the food-processing sealants guide. For walk-in coolers and freezer panels, the walk-in cooler and freezer sealant guide covers low-temperature application and panel-joint details.

Infrastructure and paving: traffic-bearing polyurethane for parking decks and sidewalks; specialized cold-applied or hot-poured formulations for bridge decks and PCC pavement. See the bridge expansion joint guide and the highway and pavement joint sealant guide. For crack repair on slabs and walls (rigid filler vs flexible sealant vs self-leveling), see the concrete crack repair guide.

Building envelope and sound control: paintable elastomerics for siding, trim, and cladding joints, butyl and silicone for roof flashing and penetrations, and acoustical sealant for sound-rated wall assemblies. The best caulk for exterior siding guide covers gap sizing and chemistry picks, the commercial roofing sealants guide covers flashing and penetration details, and the acoustic sealant guide explains where a wall assembly needs sealant to keep its STC rating.

Cross-reference a competitor part number

If you have a competitor part number from Boss, DAP, Hilti, OSI, Sika, 3M, or another major brand, the sealant cross-reference looks up an in-stock equivalent with current pricing.