Sealant Chemistries

Joint Sealants can be broken down into six primary categories:

  1. Acrylics
  2. Butyls
  3. Latex
  4. Polysulfides
  5. Polyurethanes (PU)
  6. Silicones
  7. Silyl Modified Polymers (SMP)

1. Acrylics (solvent-based) Paint

  • Used in residential and light commercial construction, mainly for exterior applications
  • Generally meet ± 12.5% movement (ASTM C 920, Class 12-1/2)
  • May need special handling for flammability and regulatory compliance
  • Can be painted
  • Short open time; difficult to tool
  • Exhibit some shrinkage upon cure
  • Often used for perimeter sealing and low movement joints

2. Butyls (solvent-based)

  • Excellent adhesion to most substrates
  • Excellent water vapor transmission resistance
  • Limited movement capabilities, generally up to ± 10%
  • Excellent weathering
  • Sometimes used in curtain wall applications where adhesion to rubber compounds is needed
  • Most are stringy and difficult to apply neatly
  • May show some shrinkage after cure; may harden and crack over time on exposed surfaces
  • Some are not suitable for application where exposed to UV
  • Some are non-hardening and are suitable for concealed application where sealant needs to remain pliable

3. Latex (water-based, including EVA, acrylic – also known as "caulk")

  • JulyGun.pngCourtesy AlbionUsed mainly in residential and light commercial construction applications
  • Interior and exterior use
  • Premium products meet ± 25% movement (ASTM C 920, Class 25)
  • Excellent paintability (with latex paints)
  • Very good exterior durability
  • Exhibit some shrinkage after cure
  • Not used for exterior applications, particularly on high rise construction, for applications undergoing significant cyclic movement,  or for high-profile structures

4. Polysulfides

  • First “high performance” sealant; mainly used in industrial applications (ASTM C920, Class 12-1/2 or 25)
  • Poor recovery limits their use in joints with high cyclic movements
  • Can be formulated for excellent chemical resistance (especially for aviation fuel)
  • Good performance in submerged applications
  • Require a primer on almost all substrates

5. Polyurethanes (PU)

  • Used in industrial and commercial applications
  • Very good movement capabilities, up to ± 50% (ASTM C 920, Class 25 and 50).
  • Not used in SSG applications (avoid direct contact to glass)
  • Excellent bonding, generally without a primer for many surfaces
  • Can be formulated for good UV resistance, which may be compromised by a selected color
  • Paintable
  • Some formulations may contain low levels of solvent

6. Silicones

  • NYCondoPicture of a NY Condo built using silicones Structural bonding and structural sealant glazing (SSG) of glass to frames
  • Excellent joint movement capabilities; can exceed ± 50% (ASTM C 920, Class 50 and Class 100/50)
  • Excellent low temperature movement capability
  • Excellent UV and heat stability
  • Good adhesion for many substrates especially glass; a primer is recommended on certain substrates, particularly porous substrates
  • Not paintable
  • Used in protective glazing systems and insulating glass units to improve thermal performance (reduce heat loss). Also used for missile impact and bomb blast situations
  • Acetoxy chemistry based sealants have strong odor, but newer chemistries have very low odor
  • Adhesion, as for all sealant types, is adversely affected by less than perfect application conditions
  • High, medium and low modulus sealants available
  • May stain some types of natural stone without primers. Low staining potential formulations are available

7. Silyl Modified Polymers (SMP)

  • One of the newest sealant technologies
  • Enable broad use in construction, industrial, DIY, automotive, marine and transportation markets (not recommended for structural sealant glazing applications)
  • Excellent adhesion and movement capabilities; good UV and heat stability
  • Paintable
  • Provide exceptional bonding to plastics, metals, wood and stone
  • Can exceed ± 50% joint movement capability (ASTM C 920) even in low temperatures
  • Contain no solvent, contribute less VOC, and yield lower odors compared to other chemistries