I’M WORKING ON A JOB WHERE THE PLUMBERS PUT RADIANT HEATING IN THE BATHROOM AND THE HOME OWNER WOULD LIKE ME TO PUT IN THE CONCRETE. I AM TOLD THAT LITEWEIGHT CONCRETE IS THE WAY TO GO.I’VE PICKED UP SOME PERLITE AND WAS TOLD TO SUBSTITUTE THE AGGREGATE [SAND] WITH THE PERLITE.CAN ANY ONE TELL ME WHAT THE CORRECT RATIO OF PORTLAND CEMENT TO THE PERLITE IS.THIS IS IN A SECOND FLOOR BATH THAT IS GOING TO BE TILED BY THE WAY. THANKS FOR ANY HELP I CAN GET. REGARDS,NORM