High Performance Bonding Compounds for the Composites Industry

ProTip: Versatile Vinyl Ester

By Bob Cottrell, CPIM

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Ben Zobrist recently signed a $56 million contract with the Chicago Cubs.  Why did they pay him such  a huge amount of money?  It wasn’t because he hit for the highest average or had the most home runs.  It was because of his versatility – of the nine baseball positions, he has played five and is a “switch hitter”.  He has been called a “super utility player”.  Versatility is valued in sports, as it should be in business.

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Arjay’s 7121 Vinyl Ester Bonding Compound, like Ben Zobrist, has proven to be an extremely versatile product in our customers’ arsenal.  It is used for the expected critical bonding applications such as:

• Stringers to Hull (shown, right)
• Liner to Hull
• Deck to Hull

When the above applications utilize a standard medium weight bonding compound, 7121 offers much higher tensile strength, tensile elongation and better lap shear.  While customers appreciate the improved quality of their boats associated with the intended applications, we are impressed with the unintended applications which they have found to utilize the superior physical properties of 7121: 

Mold Repair

Mold flanges take a beating during the pulling process.  A misdirected putty knife can take a chunk out of the flange – laminate as well as tooling gel coat.  Customers have found that filling the depressions with 7121 provides a durable, tough repair that lasts.


Radius Compound

Some customers building vinyl ester parts are using 7121 as a radius compound.  They like the fact that it is vinyl ester based, and more compatible with their laminating resin.  From a wet on wet standpoint it facilitates an improved coordination of the gel and cure times of the two resin systems.


High Vibration Areas

7121 is being used in bonding and filling applications in and around the transom.  Its excellent tensile elongation allows it to hold up to the vibrations from the engines.  Certain competitive products with even greater tensile elongation have been reported to result in excessive movement resulting in gel coat cracks.



One customer building a vinyl ester boat uses 7121 to fill the strakes.  Certainly there are more economical alternatives, but they prefer to maintain vinyl ester resin throughout their construction.


The above applications were entirely due to our 7121 customers realizing the versatility of this product and applying it to situations where they needed solutions. They appreciated the versatility of 7121 apparently as much as the Cubs appreciate the versatility of Ben Zobrist.