SEA walls designed to protect vulnerable coastlines from erosion by the sea are themselves at risk from the pounding of the waves. It's a problem likely to get worse if sea level rises or storms become more frequent because of global warming.

To protect these sea defences, the German chemical firm BASF has developed a spray-on polyurethane coating that is now being tested on the shores of the North Sea. Made by mixing two chemicals - a polyol and isocyanate - the coating can be applied directly to a loose layer of stone using a high-pressure spray, or mixed with crushed stone and sprayed in layers up to 30 centimetres thick. It cures in about 20 minutes, creating an elastic surface peppered with pores a few centimetres in size.

"In a conventional boulder and concrete reinforcement, the surface gets the full impact of the wave and starts to break away," ...