Substrates for VM ZINC® applications Laying zinc sheets on a continuous substrate is part of the traditional roofing method. In order to ensure the durability of VM ZINC®, the substrate must meet the following requirements: . Geometrical continuity: The substrate is considered to be continuous when there is no more than a 5 mm difference in height (flush tolerance) between its components at their junction. There should be no protruding elements on the substrate (e.g. screws or nails) that could damage the underside of the zinc. The roofing company responsible for the installation of VM ZINC® must check that these minimum requirements have been met. . Project Structural conformityaccording to the loads: the building design team should make sure that the project loads are compatible with the performance of VM ZINC® systems. These loads include, in particular, the weight of the system, live loads, loads due to climatic constraints as well as the effect of wind. . Physico-chemical compatibility of material in contact with zinc. The geometric continuity, structural conformity and physico-chemical compatibility of the VM ZINC® substrate should be studied at the design stage of the roofing or facade complex in order to select the appropriate VM ZINC® system.      Compatible timber roof decks      Plywood and treated wood      Zinc in relation to other materials      Zinc in relation to other metals Compatible timber roof decks Because techniques are simple and adaptable and the material malleable, the most frequently used roof substrate is close-boarding of a timber compatible with zinc. Boarding of solid timber with a pH between 5 and 7 is the safest direct substrate and the most suitable for zinc roofing. Timber with a pH less than 5 is forbidden because of its corrosive action on the metal in damp conditions. Acceptable timbers Forbidden timbers Pine Larch Spruce Oak Scots pine Chestnut Poplar Red cedar Douglas fir White cedar Plywood and treated wood Direct contact between zinc and plywood or chipboard is forbidden. These panels may be made of acid timber types, or of timbers containing tannins, and may contain phenolic adhesives: all three factors increase the risk of corrosion on the underside of the zinc. In addition, they are not good at absorbing humidity beneath the zinc and allowing its removal by means of a ventilated air gap. If these materials are used, VM ZINC® recommends using exterior quality treated plywood panels (insecticide fungicide). To allow the installation of titanium zinc on this substrate VM ZINC® recommends using VM ZINC® PLUS (titanium zinc protected on the underside) or the DELTA VM ZINC® separation membrane. Zinc in relation to other materials Bituminous felt: Bituminous felt is forbidden in direct contact with zinc because of the risk that water may be retained. Since the water cannot be removed from the felt, it will constitute a corrosion risk. If felt is used, a neutral membrane such as DELTA VMZ should be used. VM ZINC® PLUS can also be used a foil allowing correct VM ZINC® expansion since both the protective coating on the underside and the foil will avoid any problem . Care should be taken not to lay VM ZINC® PLUS on an abrasive substrate to avoid damage to the protective coating due to movement caused by thermal factors. Concrete: Laying directly on concrete or reinforced concrete is not recommended except when using a DELTA VMZ separation membrane or a timber decking with ventilated underside with VM ZINC® PLUS. Zinc in relation to other metals Various metals can be classified in accordance with their reactivity potentials, relative to the normal hydrogen electrode. If two metals are in contact, the metal with the higher potential in the electrochemical ranking decomposes the metal with the lower potential and, by accelerating corrosion, destroys it after a certain time. In practical terms, a certain number of bimetal contacts are acceptable while others must be avoided. This is particularly important when installing lightning protection. In addition, water must never be allowed to run from a higher potential metal to a lower one: the water can contain charged ions which would accelerate the removal rate of the weaker metal. For this reason you should install metals in the following order, from top to bottom: aluminium (top), zinc, galvanised steel, lead, copper (bottom). Acceptable contact metals Lead There are no associated problems with this metal Aluminium Although a lower potential, it has a similar protective coating, thus the two metals have very similar potentials, eliminating any risk of corrosion. Galvanised Steel Galvanisation coats the steel with a fine film of zinc. This zinc-zinc contact poses no problems. Stainless Steel Austenitic stainless steel and lead or tin-coated ferritic stainless steel is permissible. Unacceptable contact metals Copper Steel (Non galvanised)