Page 24 - Professional Parquet July 2013

ON FIELD
Risk classes (extracted from Standard En 335)
Risk class
Situation
Risk class 1
Situation in which the wood or wood-based product is completely under cover, protected against weather conditions and not exposed to wetting. In this environment, the moisture content of wood is such that the risk of attack by surface mold, blue fungi stain or xylophages fungi is insignificant. The maximum moisture content of wood must be maximum 20% for practically the whole of its service life. However it is possible to have attacks from xylophages insects including termites but the frequency and the magnitude of the insect risk depend on the geographical region.
Risk class 2
Situation in which the wood or wood-based product is under cover and fully protected from the weather, but high envi- ronmental humidity can cause occasional, but not persistent wetting. In this environment the % of moisture content of the solid wood is sometimes greater than 20% in all or only in some part of the element, thus allowing the attack of xy- lophages fungi on the wood, which is also employed for decorative functions. There may be a change in appearance due to the growth of surface mold and staining fungi. The risk of insect attacks is the same as indicated in Risk Class 1.
Risk class 3
Situation in which the wood-based product is not under cover and not in contact with the ground. It is either continually exposed to the weather or is protected from the weather but subject to wetting. In this environment, the wood can often have moisture content greater than 20% and therefore will be frequently exposed to the attack of xylophages fungi on wood, which is also employed for decorative functions. The risk of insect attacks is the same as indicated in Risk Class 1.
Risk class 4
Situation in which the wood-based product is in contact with the ground or fresh water and thus is permanently exposed to wetting. In this environment the wood has a moisture content that is permanently greater than 20% and is exposed to attack by xylophages fungi. In some geographic regions, the termites can also be a problem furthermore in certain environments such as fence posts, the portion situated above the ground or water is exposed to possible attacks of xylophagous beetles.
Risk class 5
Situation in which the wood or wood-based product is permanently exposed to salt water. In this environment, the wood moisture content is permanently above 20%. The main problem is the attack of invertebrate marine organisms especially in warm waters, in other words where organisms such as limnoria spp. and teredo spp. can cause severe damages on the portion that emerges from the water, such as piers that may be exposed to xylophages insects such as termites.
IN-DEPTH ANALYSIS
centage, as well as the provenance of plant species, and the location where the plant has grown, and sometimes even to the environmental conditions where the wood is utilized.
The durability of the wood
The main cause of the degradation of the wood, therefore, is the water in its all possible forms, other cause of deteri- oration is the attack of xylophage in- sects (very little relevance with respect to the first one), in relation to this, it is very important the choice of wood type, identifying the most suitable one to confer durability to the work.
To achieve the best result, it is necessary to start from areas where trees grow, places of exposure and the cutting, methods of aging, the loss of its founda- tion water until reaching an equilibri- um with the environment, and tech- nologies of sawing; the best time period for cutting is autumn and winter with a waning moon, when the plant is not "grafted".
In the past, when exotic wood species were not widely known and diffused,
we tried to stem the deterioration of wood by chemical preservation, first manually, then with technologies of im- pregnation with chemical elements un- der high pressure with autoclave. To- day, we treat timbers in autoclave with less harmful chemicals than before to ensure durability and structural safety. This result is also obtained by naturally durable wood species.
By definition, the "natural durability" is the ability of a wood kind that resists degradation caused by humidity and lignivorous insect attacks without preservative treatments. The durability concerns only the heartwood, whereas the sapwood of all timber species should never be taken into considera- tion. The standard En 350-2 contains the list of over a hundred wood species of conifers and broadleaf trees as well as tropical ones that have the characteristics of natural durability. The standard En 335 introduces the concept of biological risk class, which
is defining 5 situations depending on the humidity of the environment in which the wood is 'alive'. R