Some of the sort of chipboard inside a thin strip of kitchen worktop behind the sink has rotted away. The area was being used to dry stuff and obviously that's how the problem developed. The water was leaking in via an area of rotten caulk and damaging the worktop at the far end near the wall tiling. I removed all the caulk but now want to firm the area up somehow before adding new caulk. The laminate layer on top is fine but shows a slight concavity. Because of the hollow under the laminate however it bends in further with any pressure, thus it's not rigid enough to support new caulk to seal the edge of the worktop to the tiles. What should I use to fill in the damaged area? Expanding foam filler? I need something to fill out a gap that's difficult to access because it's under the laminate, and there's overhanging tiles. Just enough of a gap at wall to stick a thin nozzle in. It's not a large area, probably 6cm wide area affected.