How to Check Whether Wood Will Last for Years? Ageing and Fire Testing Without Myths

Despite the dynamic development of technology and the emergence of new materials, wood still remains one of the most important raw materials. This results from its renewability and natural origin, which translates into a low carbon footprint and even a negative CO₂ balance. Wood and wood-based materials, such as plywood, are characterised by relatively low density combined with high mechanical strength. On the other hand, they are susceptible to destructive factors such as water (causing swelling, shrinkage, cracking or warping), fungi, insects and fire – wood is a combustible material.

Most domestic wood species are characterised by medium or low natural durability, therefore they require appropriate protection. In order to increase the durability of wood, protective agents such as paints, varnishes or impregnating agents are commonly used. However, it is crucial that the preparations used effectively protect the material and extend its service life, while having minimal impact on its functional properties. A longer lifespan of wooden and wood-based products directly contributes to reducing the carbon footprint.

Manufacturers of paints and varnishes offer a wide range of products intended to increase the durability of wood. However, the question arises whether these agents are properly selected for the specific wood species we want to protect. In technical specifications, it is rare to find information on which wood species ageing tests were carried out, and often it is not known whether such tests were carried out at all. Can the user independently verify how protected elements will look after several years of use? It is possible; however, tests in natural atmospheric conditions are time-consuming and, in accordance with PN-EN 927-3:2019, last appropriately long.

An alternative is accelerated testing conducted in a QUV chamber, for example in accordance with PN-EN 927-6:2018-10 “Paints and varnishes – Coating materials and coating systems for exterior wood – Part 6: Exposure of wood coatings to artificial weathering using fluorescent UV lamps and water”. After just several weeks of such testing, it is possible to obtain information on how a building façade or garden gazebo will look after 5, 10 or even more than a dozen years of use (depending on the duration of the test). During the tests, among others, changes in colour and gloss, as well as the occurrence of cracks and coating delamination, are analysed. All paint and varnish products, such as impregnating agents, varnishes or enamels, as well as various wood species, may be subjected to testing.

In recent years, an increase in customer awareness regarding fire protection regulations (fire safety) for wooden buildings has also been noticeable. Increasingly, wood or wood-based materials, such as plywood, protected with fire-retardant agents are used. Such a product should be classified in accordance with EN 13501-1, on the basis of the SBI reaction to fire test carried out in accordance with EN 13823. The production of such products takes place under the supervision of an independent notified body, which allows for the granting of a CPR certificate (Construction Products Regulation – EU Regulation No 305/2011 laying down harmonised conditions for the marketing of construction products). This ensures that the product meets all requirements and that responsibility for its properties rests with the manufacturer.

In the case of independently protecting wood with a fire-retardant varnish, it is absolutely necessary to check on which wood-based material the given agent was tested. The best solution is to carry out an SBI test on one’s own product. In such a case, full responsibility rests with the investor, and not with the manufacturer of the varnish or other protective agent.

An important issue is also the possibility of using fire-retardant products on the exterior of buildings. A fire test alone is then not sufficient, because it does not provide certainty that the material will not lose its properties during use under the influence of atmospheric conditions. EN 16755:2017 indicates that moisture may cause crystallisation of flame-retardant agents, particularly those based on salts, on the surface of wood impregnated with retardants. As a result, the fire-retardant agent may be leached from the surface of the wood, leading to a weakening of its non-flammable properties. The content of flame-retardant substances in wood may decrease as a result of rainfall, changes in humidity and the action of UV radiation.

For these reasons, the functionality and long-term durability of fire-resistant wooden products should always be verified not only by means of the SBI test, but also through ageing tests in a QUV chamber or in external conditions. After such an ageing process has been carried out, the reaction to fire test should be repeated. Only then can one have real certainty that the building is safe in practice, and not merely compliant with formal requirements.

Paged LabTech has the capability to conduct durability testing of coatings on wood in accordance with PN-EN 927-6. The method includes exposure in artificial atmospheric conditions using fluorescent UV lamps and water, and the samples are placed in a QUV chamber for accelerated ageing tests, where in a cycle including condensation, UV radiation and spraying, conditions corresponding to approximately five years of natural external exposure are reproduced. Laboratory tests are supplemented in parallel with field tests, which allows the development of microorganisms, impossible to fully reproduce in chamber conditions, to also be taken into account. Evaluation is carried out after 2, 6 and 12 weeks and includes, among others, analysis of gloss loss, the formation of cracks, blistering and colour changes.