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Materials Metals and timber

could cause corrosion problems. All metal fixings should therefore be of appropriate corrosion resistance and should be compatible with the timber species being used and with any preservative treatment specified.

Iron stain Iron stain is the result of a chemical reaction between iron and tannins or tannin-like materials in the timber that contribute to form iron tannin compounds. Commonly described as iron tannate, these compounds form a blue/black stain that can develop in damp timber in contact with ferrous metals Metal connections on Deal Pier. such as iron and mild steel. Photo: Price & Myers Iron stain is most commonly associated with oak, but also with sweet chestnut, makore, idigbo and kapur. Softwood species prone to iron stain include Douglas fir and western red cedar.

Metal connections on Deal Pier. Photo: Price & Myers

Some fire-retardant salts also promote the corrosion of metals and can raise the moisture content of treated timber. The potential of preservatives and fire retardants to corrode metals increases as the moisture content of the timber rises. The manufacturer of the wood treatment product must be consulted about the appropriate fixings to be used. There are other fire retardants with active ingredients that are not corrosive to metal fixings.

Seawater The potential for corrosion by timber of metals increases in the presence of salt water and salt water spray. For example, to counter this effect, austenitic stainless steel fixings for roof battens may be used in locations close to the coast, while galvanised steel fixings may be suitable for low-risk locations away from the coast.

Swimming pool halls Provided the appropriate measures have been taken, the moisture content of timbers in swimming pools will not generally be high enough to be the direct cause of corrosion in metal fixings. However, occasional but repeated wetting, and/ or condensation on glazing and chemicals in the atmosphere, www.trada.co.uk

Iron stain can arise where ironworks have been carried out near to the affected timber. It can be avoided by keeping ironworks and timberworks separate and/or by carrying them out at different times in the building process. >>

Dos and don’ts when using metals with timber • Where possible, use a timber species that is less likely to corrode metals. • Use metals, metal alloys or coated metals (for example, galvanised or powder-coated) that are less likely to be corroded by timber. • Separate metals from timber using drainage and ventilation gaps, inert materials such as plastic and/or impermeable membranes (for example, vapour control layers, dampproof courses impregnated breather membranes, bitumastic coatings and protective paint systems). • Avoid contact or close proximity between different metals. • Consult manufacturers of metal products to ensure the correct procedures are followed and that compatible materials are used. • Consult manufacturers of wood preservatives and fire retardants to ensure correct procedures are followed and compatible materials are used.

Timber 2019 Industry Yearbook

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Profile for BM TRADA

Timber 2019 Industry Yearbook  

The annual publication of the Timber Research and Development Association (TRADA) includes topical and technical features on all aspects of...

Timber 2019 Industry Yearbook  

The annual publication of the Timber Research and Development Association (TRADA) includes topical and technical features on all aspects of...

Profile for trada
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