THIRUVANANTHAPURAM: Erecting red gypsum blocks to protect houses in the coastline against rough seas will begin at Vettucaud on a trial basis from Thursday. The corporation plans to use red gypsum to build protective walls where rough sea causes massive destruction on houses in areas such as Valiyathura, Vettucaud and Shankhumukham. With the cooperation of Travancore Titanium Products Ltd, red gypsum which is the residue in titanium production, will be used in blocks to build the walls. The blocks developed by the research unit of Travancore Titanium has 46 percent red gypsum, 36 percent sand and 18 percent cement in it.