Fältförsök med träskyddsmedel för klass AB
Resultat efter 15 års exponering
Field trial with wood preservatives for class AB. Results after 15 years' exposure
In 1996 a field trial was set up in order to get information about the durability in ground and above ground of wood treated with preservatives intended for above ground use. Results after 3, 5 and 10 years' exposure have been presented in previous reports (Johansson et al 1999; Johansson et al 2001, Edlund et al 2006).
Samples were treated according to Nordic wood preservation class AB with the following preservatives: Basilit Bauholz KVD, Impralit KDS, Kemwood ACQ 1900, Tanalith E, Wolmanit CX-S and Wolmanit CX-8. Untreated spruce and heartwood of pine and larch were also included in the trial. In addition to testing according to modified versions of EN 252 and ENV 12037 (lap-joint), testing was also carried out according to methods specially designed for this trial. In 1997 wood treated with Scanimp KF, a waterborne metal free wood preservative, was added to some of the test procedures.
After 15 years' exposure it can be concluded that:
- The progress of decay is slower in the above ground samples than in the samples in ground contact. However, the ranking with respect to the performance is still roughly the same.
- Wood treated to preservation class AB (= Use Class 3 according to EN 335-1) is not recommended for use in ground. The service life can be expected to be approximately 10 years.
- Wood treated with the copper-organic type wood preservatives used today performs generally better than wood treated with metal-free preservatives as well as heartwood of pine and larch.
- Based on experience from the above-ground trials class AB treated wood will have a service life of at least 20 years, providing it has been used correctly and will thus comply with the 20 years' warranty provided by the Swedish Wood Preserving Association. However, end-uses close to ground may be critical. A majority of samples in the mini-deck trial were slightly attacked by decay after 15 years and it is necessary to be aware that:
− the test samples consist of 100 % sapwood with full penetration of wood preservative,
− in practice decking boards etc will consist of approximately 50 % heartwood,
− heartwood in the wood surface will be critical for the service life,
− sub-standard penetration will affect the service life,
− present retentions for the copper-organics approved by the Nordic Wood Preservation Council (NWPC) are lower than those applied in the trial.
- A comparison between results from five years' testing in ground according to EN 252 and 15 years above ground according to ENV 12037 (lap-joint) and the mini-deck method shows some similarities in the ranking of the wood preservatives. However, there is no obvious general correlation between testing in ground and testing above ground with these methods. Thus, there is no simple way of translating results from trials in ground to results from trials above ground. Further work and analysis of results from several trials are required in order to be able to use results from in ground trials for approval of wood preservatives to class AB (Use Class 3).
- Samples treated with metal-free preservative and subsequently coated performed reasonably well. However, the real effect of the coating was difficult to evaluate, as neither uncoated preservative treated nor coated untreated samples were tested.
- Reference preservative TBTO got severely attacked by decay after 10 years and its role as reference preservative should be discussed.
- Preservative-treated wood has in general enhanced the corrosion of fasteners compared to untreated wood. No corrosion was yet observed on stainless steel, whereas mild steel was heavily corroded.
- The trials have confirmed the classification of the natural durability of pine (Pinus sylvestris) and larch (Larix decidua) according to EN 350-2.
- Pia Larsson Brelid, Jöran Jermer, Ingvar Johansson
- SP Sveriges Tekniska Forskningsinstitut
- Originalspråk: Sv