Grey Mountain bought into the company five years ago.
Financial terms of the deal were not disclosed.
Robbins has almost 200 employees across three facilities in the southeastern US, and manufactures custom mixed rubber compounds and moulded rubber products.
Grey Mountain is currently investing from its second fund, which closed on $225m in 2010.
Grey Mountain’s last reported deal was the purchase of substantially all the assets of Hawkins Glass Wholesalers’ flat glass division in February.
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