Soft Soldering @museum.de

Have you ever come across this? The most stylish gutter in the world is no good if the seals between the individual sections aren't watertight. It will continue to drip and dribble for hours after the rain has stopped. That's when you're grateful to have a real metal roofer to hand who has mastered the art of soldering.

In soldering, two sheets of metal are joined together by placing them on top of each other and treating them with soft solder. Soft solder is 40% tin and 60% lead. It's exposed to such high heat that it liquefies and runs between the sheets of metal. The canny metal roofer makes use of the capillary effect: the smaller the gap between the sheets, the more the melted solder is drawn into the intervening space.

But first, the sheet metal needs to be cleaned and coated with flux. Then a few soldering points are placed to fix the two sheets in place. And finally, the seam is carefully soldered until it's watertight and can be cleaned to finish off.

Soldering requires more than just craftsmanship. The metal roofer must also be familiar with the physical properties of his materials – especially their melting points. If he heats the solder or the soldering iron to a level that exceeds the melting point of the material– the gutter, say – then he'll soon find himself struggling with a molten workpiece. And he'll have blown it.

Ventilation is crucial. Outdoors, on a building site, there is no danger. After all, you're working in the open air. But here, indoors, you have to watch out for harmful vapours that arise when the solder melts. So, if you're soldering indoors as an amateur sheet metal worker, always use a fume extractor!