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Linolie til overfladebehandling af udvendigt træværk 10. English summary
The research revealed a big difference in durability of the treatments as well as in their ability to protect the wood. Some places both treatment and wood were quite destroyed whereas other places showed a fully intact treatment and a woodwork in good condition. Moreover, there were also cases where the top coat was crackled and had other imperfections, but the wood was still well protected. 10.1 Background and purposeExterior woodwork must be treated on the surface to prevent decomposition of the wood as a result of the action of light and humidity. The treatment is not without problems, though. Much simplified the known remedies are either not efficient enough or they are poisonous or in other ways a strain on the environment: The production of the remedies may involve extensive use of energy or they might be produced from non-renewable raw materials. Wood preservatives thereby become one of the big environmental problems in building. Wood preservatives cause problems throughout the life cycle: in the production, in the application, and in the disposal of it – problems to surroundings as well as work environment. The poor durability and the frequent maintenance of outdoor woodwork incite the use of other materials, such as plast or aluminium with high demands of energy in its production together with other environmentally harmful effects. Till around the end of the 1970s wood preservatives were based on different oils and diluted with turpentine or other organic solvents. The bad work environment led to the development of emulsion paints and wood preservatives based on water which was good for the painters but hardly so for the wood; the first generations of these new paints had very poor protective properties. These experiences along with a growing concern about the environment led to a renaissance of linseed oil which has been the traditional product of wood preparation for centuries. Linseed oil became a popular commodity - the market received it well. However, the products used today are not the same as the "historical products". Among other things the old linseed paints contained large quantities of lead which is a most efficient fungicide. In reality, no or only limited documentation for treatments with modern linseed oil products existed. In turn many myths have prevailed about linseed oil and its properties. Therefore, there was a need for research where the current knowledge of linseed oil could be summed up and its suitability as wood protection was more closely examined in practice. The research is supplemented with a lexical section that explains the key words and concepts not commonly known. This project is a continuation of experiments with window renovation and linseed oil treatment executed in connection with the Øksnehallen Project (Lading og Brandt: "Vinduesistandsættelse og linoliebehandling", By- og Boligministeriet 2000 - not translated). 10.2 The ResearchThe main purpose of the research was to receive an impression of how the products work in practice. This was to be done by evaluating the condition of building parts that had been treated with linseed oil and been exposed to wind and weather for some years. To be able to draw conclusions from the condition assessments the following demands were made of the treatments:. They should be
and
However, it turned out to be difficult to find suitable objects of examination. Partly, it is limited how many new treatments have been executed before 1995. And partly, many of them are not very well substantiated or they have been exposed to mixed treatments (where e.g. alkyd paint has also been employed). Another characteristic is that linseed oil is employed especially in the restoration of historical buildings or by private "do-it-yourself-people". This is also reflected in the examined treatments found on 6 mansions and listed buildings, 1 terraced house, and 6 cottages at the Open Air Museum – plus one apartment block that was the only example of an "ordinary building". Some manufacturers have in recent years developed linseed oil paint that can be sprayed on and which is primarily used for factory treatment of new windows. These products have not been on the market long enough to be part of the research. Also, it must be noted that in a lot of the cases the products employed no longer exist on the market. Some manufacturers have closed down, others have changed their special mixture of ingredients. All of the examined products have been treated with linseed oil applied by brush and all executed on existing woodwork of which some have been mended with new wood. 10.3 ConclusionsAs mentioned some of the examined treatments proved to be extraordinarily durable – others absolutely not. In some cases the wood were in good condition even though the paint film did not look very well. In turn, no examples showed wood in a poor condition under an almost intact coating – something one may meet with in cases of e.g. latex paint. On the whole, too many imperfections were found even though the research includes only a relatively moderate number of treatments. The imperfections were found in both workmanship and products. In all examined examples (except from a barn in Vemmetofte) professional technical consultants took part in the construction work – also consultants specialised in restoration. Still, there turned out to be big differences. This was mainly due to three things: the quality of the wood, the products, and the application. The experiences from this project and from the Øksnehallen Project show the decisive importance of the following factors for a good result:
It is obviously difficult for both consumers and professionals to get the right information and to choose the right products. Differences in quality often do not become evident until after several years, and the purchase of linseed oil products is a matter of trust. In the project group’s opinion good products can be found on the market but not an optimal system. (Painting articles normally exist available in the shape of systems, which include products for priming, intermediate coating and topcoating. Typically the products in the system will come from the same supplier, and as a premise of product guarantee a treatment must not draw on products from different systems.) Choosing products from different suppliers (e.g. priming from one supplier and topcoat from another) will cause problems in the product guarantee, and furthermore there is a risk that the products will not be able to function together. Such a solution therefore cannot be employed for professional use. Furthermore, there is also a shortage of certain product types on the market. (The report further sets out which products this implies.) There are several reasons for linseed oil treatment not having been used on a large scale outside restoration building and private building. Linseed oil treatment does not fit very well into the logistics on a modern building site. Partly due to the long drying hours and the fact that not all wood absorbs equally and therefore some wood needs more treatment than others. To sum up: the conclusion is that linseed oil may protect wood for a long time but
10.4 Research results10.4.1.1 Product imperfections There is a difference in the quality of linseed oil products, which is partly due to the fact that there is generally too little knowledge of the factors influencing the properties of linseed oil. But a number of product imperfections also suggest that not everybody in the trade has the necessary professional background and expertise:
It should be stressed that also a lot of good products are found on the market. The problem is the difficulties of finding out which products are good and which are not. One can ask for technical data but there is a great difference in the level of information since no standards exist for what they should contain. One can check if a so-called CE/EN 927 test has been carried out (where a skirting board with paint is exposed outdoor for a year). 10.4.1.2 Application The factor which in all probability has most influence on the protection of the wood is the priming. It is the priming that protects against humidity while the function of the topcoat is primarily to protect against decomposition by light (UV-radiation). The priming must saturate the upper layers of the pores of the wood with oil so that there is no "room" for humidity. When treated it is therefore important that the wood is dry (max. humidity 12-15%). Linseed oil paint must be applied in thin layers and one layer must be throughly dry before the next one is applied. In cold weather (below 5-10° C) it is difficult to apply thin layers and the drying becomes slower. The same thing happens in damp weather. The paint is not fast until dry, and destruction of the paint will therefore happen faster. It can be difficult for unskilled users (anyone not experienced with linseed oil) to obtain a satisfying result. It is a matter of experience when the priming is adequate, the paint must be coated in a very thin layer and the necessary (long) drying can be a problem. Fungicide Two types of fungicide exist: against dry rot and against mould and mildew. The first one is listed by the Ministry of the Environment and biocides are added. The other one is added to most types of painting articles for outdoor use. If a product just says "containing fungicide", it will be against mould and mildew, and usually it will be to prevent the product from being damaged before use. There is no linseed oil products with fungicide against dry rot on the Danish market. Priming products with fungicide against dry rot, which probably also contain some linseed oil, do however exist. It has not been possible in all the examined cases to find out whether the woodwork apart from having been treated with linseed oil products also have been treated with a priming oil against dry rot. Woodwork treated with fungicide against dry rot is probably, other things being equal, in a better position for resisting a wrong application than wood not treated with fungicide. Conversely, a correctly performed treatment, were the priming has been properly carried out, will probably be able to give sufficient protection. Humidity will not be at such a high level that mould and dry rot will develop. Though, it is important that the treatment (the priming) is maintained. The linseed oil paint (topcoat) must be added fungicide against mould and mildew to prevent growth of fungi. No "harmless" fungicides exist: they cannot be efficient without also having undesirable effects - that is, chemical as well as "natural" products. Generally, one ought to prefer those products where desirable as well as undesirable effects are known. There is a potential in limiting the use of fungicide to those places were it is necessary instead of treating all woodwork (as done with vacuum impregnation). Normally, it is easy to predict were the risk of rot will be – e.g. 95% of the rot attacks in windows are found in the bottom part of sashes and frames. Logistics Linseed oil treatment does not fit in very well in the logistics at a modern rational building site – especially not if other work is to be carried out at the same time. Long drying hours, sensitivity towards dust and mechanical influence ("friction") are some of the factors that make it difficult. The most durable of the examined treatments had been performed most carefully: after the priming the windows were treated with 5 coatings of linseed oil paint applied with an interval of one week – that is, a total duration of treatment of min. 6 weeks. Such a long duration of treatment will be hard to carry through in ordinary building, e.g. within urban renewal. Preferably, linseed oil painting should be performed in a workshop. If the treatment is to be performed on the spot, it should rather not be performed simultaneously with other work. Scaffolds mean a rise in price because of the long drying hours. Application criteria Linseed oil paint does not live up to the same application criteria as modern paints. It yellows, chalks, wrinkles up, attracts more dirt, etc. It is debatable whether it important, but not all builders are prepared for this. 10.5 PotentialsLinseed oil systems Probably, it would be possible to make use of the good properties of linseed oil and still take into consideration logistics and application criteria if linseed oil was used as priming and a 'modern' paint (e.g. aqueous alkyd) as topcoat. However, it is necessary to use paint in systems to secure a product guarantee. The manufacturer will inform you of which priming and top coatings should be used together. On the "want list" for a good linseed oil system is the following:
These products either do not exist at all or they do not exist within the same system. New windows New factory made windows treated with linseed oil exist on the market but they are not exposed to DVC-label. They are more expensive than similar windows, but this may be compensated for by its durability which eventually will result in a better over all economy – but as far as it is known, no actual documentation for durability exists. Therefore, the "want list" for new linseed oil treated windows include:
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