Galvanized steel is a protected variety of the metal using the process of galvanization to prevent and repel corrosion. Because the galvanized metal is designed to be resistant to outside harm, soldering pieces of steel that have been galvanized can pose a problem if done improperly. It is fairly simple to get the soldering on the steel done by just altering a few of the standard soldering steps for galvanized specific ones.
Clean the steel surface with a piece of sandpaper to smooth the metal where you want to solder it. The sandpaper removes inconsistencies on the metal that prevent solder from bonding to it.
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Wipe the galvanized steel along the sanded area. Use a cloth and degreaser to remove any dirt or grime from the steel as well as dust from the sanding.
Drive a pushpin through a piece of steel wool near the galvanized steel. The steel wool should be close enough to the metal that you don't have to get up to reach it while you're working.
Rub the sanded and cleaned area on the steel with liquid flux to make attaching solder easier. The flux creates a conductive surface for the solder.
Heat the soldering tool to the maximum heat setting and hold the tip against a piece of acid core solder. Turn the tool slowly to coat the tip in a thin layer of solder.
Hold the soldering tool against the galvanized steel where you want to apply the solder. Continue along the metal until you reach the end of the area you are working in.
Check the tip of the tool often while soldering to ensure there are no pieces of metal or dirt sticking to it. Rub the tool against the steel wool to remove the pieces.
Apply more flux to the steel as you solder to ensure proper adhesion. The steel should be lightly wet at all times.
Wipe the soldering area after every pass of the tool using an abrasive cloth. This will remove the excess acid form the solder.