3000 PSI AT 5 GPM THROUGH A ROTARY TIP DOES THE TRICK. IN VANCOUVER BRITISH COLUMBIA WE HAVE A MOSS AND ALGEA PROBLEM,THAT ON ALUMINUM SIDING WILL CAUSE THIS PROBLEM OF CHALKING.IF YOU ARE CAREFULL WITH THE PRESSURE YOU CAN ELIMINATE PAINTING AS THE CHALKING HIDES A PERFECTLY GOOD LAYER OF PAINT.MOBILE BUILDING PRESSURE WASH SERVICE (1969) 604 294-6860