BS EN 212:2003 pdf download.Wood preservatives — General guidance on sampling and preparation for analysis of wood preservatives and treated timber.
6 Guidance on sampling treated timber 6.1 General The effectiveness of any treatment depends on the introduction of suitable quantities of preservative to a sufficient depth below the surface of the wood to protect from biological attack, and to combat existing infection. The degree of protection required varies with the severity of the environment to which the treated timber is exposed. The penetration of preservatives into the timber is governed by three main factors: a) the properties of the preservative; b) the method of applying it to the timber; c) the permeability of the timber itself; this property varies markedly with species, with direction of penetration, and, even within a single timber, regions of different permeability (e.g. heartwood/sapwood) may be present. In practice, therefore, a wide range of preservative distribution ”profiles” is encountered within treated timber and any methods designed for the detailed examination of such materials should make provision not only for the detection and/or measurement of active components but also for the determination of their location within the timber samples or wooden members. The exact sampling technique to be employed in any particular case will depend on the factors enumerated above and, where required, should take account of the end use and location of the product. Most general sampling schemes for preservative-treated timber are designed to allow the determination of the retention or loading of a preservative either in the timber as a whole or in a specific part of the treated component. In deciding which sampling method to select, certain factors need to be considered.
The primary requirement of any sampling system is that the samples taken should be as representative as possible of the lot of treated wood. These should be selected so as to avoid knots, splits and other growth irregularities. It should be noted that samples consisting entirely of heartwood will contain relatively little preservative because, in general, heartwood is considerably less permeable than sapwood. Conversely, samples consisting entirely of sapwood will have a relatively high retention of preservative. Thus the proportion of sapwood and heartwood in a batch of timber should be considered if it is the intention to determine average retention of preservative within the batch. It should be borne in mind also that preservatives enter timber most rapidly through the end grain, and relatively high loadings are obtained in these areas. The effect of end penetration on the overall loading of a piece of timber will thus depend on the length of the timber while the contribution of lateral penetration to this total will vary with the cross-sectional area of the timber. It is therefore important that the dimensions of the wood components to be sampled are taken into account when deciding the sampling procedure to be adopted. When determining retentions from lateral or end-grain surfaces, it is necessary to appreciate the depth to which the preservative is likely to have penetrated. Pressure impregnation of a permeable timber will result in a relatively deep, even distribution of preservative within the wood while, at the other extreme, dipping or brushing an impermeable species will provide only a shallow, less uniform distribution which is confined to the outermost layers of the wood.BS EN 212 pdf download.