Two-step process for producing solid surface material with foam backing

A process of producing a cast composite article comprising a polymer matrix and two zones of different filler, said article being substantially flat with two opposing faces, a first zone of such article including one face of the article having filler at a level in the range of 10 to 80% by weight of the filler plus matrix, and a second zone including the second face opposing said first face having filler of 5 to 60% and 3 to 30% of bubbles, both by weight of the filler and bubbles plus matrix, said first and second zones forming a continuum with essentially no layer of unfilled matrix between the two zones, said process comprising the steps of forming a multi-layer composite article by casting on a flat surface or a base layer a first mix comprising polymerizable monomer and filler which will cure to give the composition of said first zone, and, before said first mix cures substantially, casting on the first mix a second mix comprising polymerizable monomer, filler, and bubbles which will cure to give the composition of said second zone, under conditions that will cause the second mix and the first mix to interpenetrate, so that there is essentially no interface in the matrix and no resulting layer of unfilled polymer, and curing the resulting composite article.