What are resistance classes?

They are consistent groups of values with which to determine the mechanical response of wood; they do not refer to a specific wood, but represent a systemisation of the values, similar to other materials such as the HA 30 for concrete.  So, for each resistance class we will have a list of resistance values (to flexion, traction, compression, cutting...) rigidity (longitudinal and transversal elasticity...) and density, which enable us to systemise the verification of guidelines for a structure.  The resistance classes usually used are those of European guideline UNE EN 338.  However, in species or groups of species of specific wood, it is possible to make the calculations with specific values for a parameter (for example, the elasticity module or resistance to flexion), if the class does not adequately represent the resistant profile of the wood in question. 

What is the difference between the classes of visual quality of wood and the resistance ones? 

In a very simplified way, the best “traditional” visual qualities tend to correspond to the best resistant classes of a determined species.  But the criteria and restrictions of the visual classifications whose final objective is appearance, do not have to coincide with the visual classifications whose final objective is resistance, the restrictions for the latter are only defined after extensive trial campaigns to breaking point.

Is the method reliable?

The whole process is backed by European guidelines, based on the experience of different countries over the last 150 years, establishing both the trial procedures and the statistical procedures prior and subsequent to same.

The visual classification system of wood for structural use consists in the inspection of the totality of the pieces through a visual examination of their singularities (knots, cracks, flaws...). By means of a simple measurement, the product is classified and assigned the resistance obtained in the trials.  Given that the resistance depends on the correct classification, a system of internal quality control is established in the lumber mill, complemented by an external control.

What are the CE Markings on lumber?

CE Markings constitute a system to guarantee the safety of some products as required by current European guidelines and incorporated into the Spanish Building Code.  Said markings will be obligatory for all structural wood used in Spain from 2008 onwards.  Amatex has been offering these markings to prescribers since 2007.   

What are the guidelines for visual classification?

They are documents in which the criteria for visual classification are established for a series of specific species as determined by predefined geographical origins.  These geographical origins can be very extensive, national, or more restricted (regional).  An example of the former would be the French guidelines NBF52001, or the Spanish UNE 56544 guidelines.  These guidelines, by their very nature, tend to fail to take advantage of the characteristics presented by the materials on reduced geographic scales, or do not take into account species that may be of great local significance.  They are consistent and safe guidelines but not always economical and/or industrially optimum.  To resolve this, guidelines are being developed oriented towards specific regional species and/or ambits.     

CESEFOR, public foundation, has developed – as the basis of the “Soria Pine” Warranty Stamp –a guideline for visual classification specifically for wild pine structural wood grown in the many hundreds of pine groves of Soria and Burgo.  The “Soria Pine” Warranty Stamp also ensures that the exploitation and subsequent mechanisation of the wood complies with the quality standards established by the Stamp, and incorporates the expertise of the area, traditionally dedicated to the production and transformation of wood.  All the pine groves included within the Warranty Stamp have been certified by the PEFC system of Sustainable Forestry.   

A reliable, traditional and sustainable material, three good reasons to make structures from Soria Pine with CE Markings, permitting innovation, design and reliability.

The guidelines for visual classification establish controls which ensure, over and above the requirements of the CE Markings, compliance with the guidelines and, therefore, the resistance characteristic of the selected material.  Firstly, there is an internal control in which AMATEX tracks the classification processes as well as that of the classifying personnel, designed and controlled by CESEFOR.  Secondly, CESEFOR carries out an external control through which the classification carried out by the company is audited, modifying where necessary the internal controls or establishing sanctions.  Lastly, control of the building work is provided in which the precision of the classification is checked, in such a way that the builder and the insurance company have total guarantees relating to the properties of the materials used, complemented with mechanical trials, if required.