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Assembly > Metal fixings - Pg. 192

192 Assembly TIP STAINING Remember that metals will stain: for example, the verdigris from copper sheeting will stain concrete green (which can be used intentionally in a design), while rust from iron and steels will stain adjacent materials brown and red. A concrete made with iron in the aggregate will also stain. Furthermore, (zinc-) galvanized mild-steel bolts used with stainless-steel structures will ultimately rust, thus spoiling the crisp finish of the steel and endangering structural integrity. Metal fixings Compatibility of metals, welding, and brazing Joining metal components, whether to make a railing, structure, gate, or seat, requires careful thought. Joining different metals can lead to corrosion. Welding, riveting, and the use of nuts and bolts are classic ways of joining two components and all are subject to problems. Welding can be very clumsy and weak if it is done without skill, while rivets and bolts need to be of compatible metals. Galvanic and electrolytic activity, rusting, and staining Galvanic (or electrolytic) corrosion results from dissimilar metals coming into contact, and the consequent flow of electrical current. An electrolytic medium--e.g. water, and especially salt water--speeds up the process. If dissimilar metals are to be used, separate them by means of a neoprene gasket or washer, by fabrics, or by the use of paints. Never place different metals touching without checking their compatibility. Ideally, make all components from the same metal. Electrolytic corrosion requires consideration when choosing metal fixings: ensure they are compatible. Metal ground fixings may well be preferred for lumber pergolas or decks, so as to protect the lumber from rotting. Table of dissimilar and similar metals Aluminum bronze Phosphor bronze Stainless steel Aluminum Cast iron Copper Brass Steel Lead Aluminum Aluminum bronze Brass Cast iron Copper Phosphor bronze Lead Stainless steel Steel Tin Zinc x x x x x o x x x o x x o x x o x o x x x x x x o x x o x x x o o x x o o x o o o o o o o o x o o x o o o x x o x x x x x x o x o x x x o o x o x o x + can be used together in all conditions x must not be used together unless isolated from each other o can be used together in dry conditions Zinc o x x x x x o o x x Tin