Why use impregnated foam backing–Why not use closed-cell backing?
This very logical question was asked, explored, tested and answered by EMSEAL decades ago. Closed-cell foams are cheap and if they worked to provide a comparable alternative to impregnated precompressed sealant, why wouldn’t we use them instead? The bottom line is they don’t work as a backing to moving, structural expansion joints. Closed-cell foams suffer greater compression set than high-quality impregnated foams. Closed-cell foams are therefore not suited to structural, moving, expansion joints. Compression set is worsened by rise in temperature. At expansion joints, as temperature rises, building elements expand causing the expansion joint gap to close down. This means that the material installed into the gap is being squeezed and heated at the same time–the perfect conditions to cause compression set. Closed-cell backed alternatives to EMSEAL’s microsphere-modified-acrylic impregnated, foam look on their faces to be similar. The backing is their considerable shortcoming. Permanen
