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ZINC-WOOD CONTACT

TECHNICAL NOTE ON ZINC CONTACT – WOOD

Corrosion by wood

Corrosion by wood can have several origins :

  • The presence of acids normally in the wood (tannic acid, acetic acid, cellulosic chain ends …);
  • The high sensitivity of wood to oxidative actions;
  • The presence of soluble extracts of wood decomposition products

As a result, woods with pH values below 5 are prohibited :

  • Chestnut pH 3.4
  • Oak pH 3.9
  • Larch pH 4.3
  • Birch pH 4.8
  • Douglas fir pH 2.9
  • White cedar pH 3.35
  • Red cedar pH 3

Also, the wood species compatible with zinc and used as a roof support are:

  • fir,
  • Spruce,
  • The Scots pine,
  • Poplar.

What the NF EN ISO 14 713-1 standard says

7.8 Contact with the wood
Zinc coated products are satisfactorily used in many applications for which they are in contact with a large number of wood species. However, care should be taken to avoid direct contact between zinc coatings and freshly treated wood with acid preservatives. Once the dried wood and preservatives have been applied, contact is acceptable, even if the wood is wet again. Highly acidic woods such as oak, chestnut, western red cedar and Douglas fir may be used with zinc coated parts, although initial corrosion may be considered. In these cases, isolation techniques may be provided, for example application of an organic coating on the contact surface.

Source: Galvazinc, Technical note on zinc-wood contact, July 2012

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