In recent years, cases have proliferated where treated wood exposed to a class of use 4 (in contact with fresh water and/or soil) has not surpassed a life of service beyond 3-6 years. This durability is well below user expectations, of the impregnant (issuing a guarantee) and the manufacturer of the protective product itself. Toto this has led to increased distrust of this type of treated wood products and the emergence of intense debate in the sector.

With this article the sector aims to launch a series of reflections to be able to make a loose and objective analysis of the possible causes that have led to the emergence of really alarming cases not only in Spain (Andalusia, Galicia, Castilla León, Catalonia,...) but in several European countries such as France and Italy.

The factors that can most influence the wood exposed to a kind of use 4 not adequately behaved is summarized in three:
• the type of protective product,
• the quality of treatment
• the area where the treated wood is exposed.

When these rapid degradation phenomena occur, the first thing you think is, Did this happen before? The answer to my judgment is that I do, though not as much as now, says Oriol Munné. There have always been one-off cases of having to replenish a % material treated for in-service behavioral problems. This could be due to several factors, but in general it was attributed to poor quality in impregnating the element (by the type of wood, treatment process, etc.). In any case, incidents of this kind had never transcended as much as they now (in number of cases and in % affected wooden elements), which makes it known that this is new and relevant.

Another frequently asked question (although it can lead us to hasty and erroneous conclusions if we are too simplistic) Is, what has changed during this time?

Based on the 3 key factors mentioned, the only one that has probably changed more significantly is the type of protective product. If we look back, less than 10 years seen, we find the definitive withdrawal of the famous CCA salts, highly used and recognized as the reference and trusted product of the sector. Products that have proliferated since then have been mostly chromium-free salts (although chromium still persists in the market), usually combining different copper sources with quaternary ammons.

Among recent cases of failures in the behaviour of treated wood, no wood treated with CCA salts has been detected, and it can be said that there has been no alternative product that predominates within the severe cases detected. As a result of the cases that occurred, reference centres that establish within their quality brands, indications on effective product retention, have in some ways been forced to increase recommended withholdings by more than one 60%.

It is common to make the mistake of thinking that the protective product is solely responsible for cases of failure.

A properly treated wood is one where the product has penetrated to the minimum required depth and has a quantity of product per unit volume (Retention) equal to or higher than the manufacturer's specifications. To determine the quality of a batch of treated wood, a sampling plan shall be followed in accordance with European standard and the above-mentioned analyses shall be followed. The reality of the sector reflects a significant deficiency in determining the quality of the wood treated. As a result, responsibility for failure can never be attributed only to the product if we do not know the quality of the treatment. In TECNALIA laboratories (AnEPROMA Partner Laboratory), in 2010 a total of the total 3.426 wood samples treated with copper salts, distributed in several batches. The results of the penetration analyses showed negative results in a total of 1.729 Samples (penetration class obtained below NP 5 according to EN standard 351:2008). This means that near the 50% samples were poorly treated. This somehow, highlights the credibility of the quality of the treated wood on the market.

Finally, the characteristics of the site where the treated wood is exposed will be decisive in the speed and capacity of biodegradation. Weather conditions, the type of soil, the presence of certain microorganisms, etc. can encourage and accelerate the neutralization of active product materials. In many cases there has been the fact that fungi present in the conflicting ground had high resistance to the compounds, what has made the protective products industry react in search of solutions that can cover a wider range of risks.

Based on the above, a multitude of conclusions can be drawn, although we will generally agree that the problem is multifactorial. The quality of wood on the market is not sufficiently controlled and there are significant indications that reflect a more than dubious quality of the wood treated for kind of use 4. Although there is not enough robust data in this regard and there is also no data on the quality of the wood treated makes 20 years, is considered likely not to have been significantly modified in this time period. As a result, everything seems to indicate that the new generation of products on the market, albeit with full guarantees of behaviour, require more care and thoroughness in the process of impregnation of wood. The possible proliferation of copper-tolerant fungi, especially in agricultural areas that have been repeatedly exposed to copper-based fungicides may also have influenced the case studies of published cases and should be examined whether or not this constitutes a growing phenomenon.

Oriol Munné Dtor.Madera-Biotek TECNALIA R&Ⅰ