PRODUCTION OF HAZARD/USE CLASS 4 TREATED POSTS SUPPLIED BY WILLIAM KIRKWOOD & SONS

Kiln Dried

After being milled, to give a pointed end and chamfered top, the machine rounded posts are kiln dried to facilitate the absorption of the preservative. Spruce is dried to around 35% moisture content and pine below 28%. This process takes approximately a week.

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High Pressure vacuum treatment of posts with preservative

The kiln dried posts are treated with wood preservative in a high-pressure vacuum system. The depth of penetration of preservatives into the posts is dependent on the softwood species. Pine accepts treatment more readily than spruce and the preservative can achieve the required penetration levels for Use Class 4. The required level of penetration of preservative, for Use Class 4, in spruce can be achieved with mechanical incising of the post.

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Incising

Incisions cut into the surface layer of the milled timber before treatment ensure a deeper impregnation of the preservative to meet EU standards for Use Class 4.

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Both spruce and pine posts meet EN335 standards for Use Class 4.

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Before treatment the posts are marked with a metal nail for tracing – the nail gives the year of production of the post. This allows the lifetime and origin of the post to be traced.