The tin is already in the paste if you want to weld the pipes you need welding tin no 404004 use for plumbing fittings metal containing soft soldering paste for soldering copper pipes in cold and hot water installation after cleaning apply a thin coat to the pipe end with the brush push ferrule into its final position and then heat it up until the shiny metallic surface of the soldering paste is visible then clean the joint with a damp cloth 250 g tub