3M™ EC-3550 B/A FST Scotch-Weld™ Structural Void Filling Compound 400mlProd Code: CTA35506 Product Info 3M Scotch Weld Structural Void Filling Compound EC 3550 B A FST is a two part, low density, flame retardant epoxy compound that can be stored, applied and cured at room temperature. Scotch Weld EC 3550 B A FST a non sag, non brittle compounds designed for void filling, edgesealing close out, corner reinforcement, local reinforcement for mechanical fixation and complex gap filling in honeycomb sandwich structures. The