Two component, room temperature curing epoxy compound

Key Features

  • Moderate viscosity
  • Electrically insulative
  • Room temperature curing
  • One to one mix ratio — rigid to flexible cure
  • Shore D hardness 70-80
  • Dimensionally stable

Product Description

Master Bond EP21 is a two component, room temperature curing epoxy adhesive, sealant, coating, and encapsulating system featuring outstanding physical properties, superb dimensional stability and low shrinkage upon curing. This moderate viscosity system has a very forgiving 1 to 1 mix ratio by weight or volume. In fact, EP21 has the unusual feature of allowing the properties of the cured system to be altered by tweaking the mix ratio. Adding more Part A (maximum allowed 2:1 mix ratio by weight) will give a more rigid cure, which allows for better machinability. Adding more Part B (maximum 1:2 mix ratio by weight) offers a more forgiving cure, allowing for enhanced impact and shock resistance. It bonds well to a variety of substrates including metals, composites, glass, ceramics and many rubbers and plastics. EP21 features solid thermal cycling resistance. It also withstands many chemicals including water, oils, fuels and many acids and bases. It is serviceable over the wide temperature range of -60°F to +250°F. The color of Part A is gray and Part B is amber. Once cured, EP21 is a highly reliable electrical insulator. EP21 is truly a versatile system and can be used in electronic, electrical, aerospace, optical and OEM applications, among others.

Product Advantages

  • Convenient mixing: non-critical 1:1 mix ratio by weight or volume
  • Variable mix ratio feature allows adjusting the type of cure
  • First rate physical strength properties
  • Moderate viscosity; even and smooth flow
  • Sound dimensional stability; low shrinkage upon curing
  • Sterling electrical insulation properties



Double Barrel Cartridge


Gun Applicator


Premixed & Frozen Syringe

EP21 is available is various sizes and units to accommodate customer's needs.

Case Studies

Researchers in Germany wrote a paper on how a miniaturized sensor for dissolved oxygen was fabricated in silicon thin film technology. In this paper, they cited Master Bond as follows. “Finally, the chip and the bond wires were encapsulated with a two component epoxy resin EP21.”1

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