I receive almost daily questions from readers interested in how to protect exterior wood. I also see such questions daily on specialized groups. It's just that there, the options proposed by other members of the group are not always correct and precisely confuse the questioner. Not infrequently I have seen recommendations such as nitrocellulose varnish or burnt motor oil, solutions that are not recommended because of their lack of resistance or high toxicity in the case of burnt oil. This is why I thought that a presentation of all the wood finishing options used in exterior projects would be useful. I specify that the presentation refers to products that can be found on the Romanian market, DIY products or those dedicated to professionals.
But before the presentation, I would like to remind you that outdoor products must protect wood against water, weather, atmospheric humidity and sunlight. Water eventually causes the wood to rot and the sun changes its surface color to bluish gray. Do not confuse this color, which shows no signs of disease, with blackish gray, showing the presence of mold. It is very important that the wood you choose is rot-resistant and that the construction system does not allow water to soak in, but allows air to circulate. Find out what you need to do to make your wooden buildings weatherproof from the outside here.
Natural oils, the oldest protection option
The protection of wood with natural oils has been known since ancient times. Over time they have been replaced by synthetic materials, which are easier to use, more accessible, cheaper and more durable. The return to natural materials in recent times has brought oils back into the limelight, rediscovering the beauty of wood finished in this way.
Natural alternatives for finishing exterior wood are linseed oil, tung oil and mixtures of these.
Linseed oil is more affordablebut the finish is not very resistant. Without added pigments it does not protect the wood against the sun's rays (the wood changes color even when oiled). It only protects against water, but because it is spălat in wet weather, the protection is not long-lasting. The advantage is that refinishing is done easily, without removing the old coat and without sanding, just by applying another coat. If the weather is very rainy and the wood is directly in the rain, refinishing will have to be done every 6 months, maximum once a year.
Tung oil is much stronger, but also much more expensive. Its darker color also makes it resistant to the sun, and the thin film it forms on wood makes it much more resistant to water. Unlike linseed oil, which doesn't dry in contact with air and doesn't form a film, tung oil makes a thin but very elastic and resistant film (it's even resistant to acetone). It protects the wood very well and the finish will last for years. Natural tung oil, pure and boiled for faster drying, is expensive, and cheaper versions are usually blends with other oils or substances.
The most popular natural blends of the two oils are Danish oil and Kreidezeit oils (you can also buy them at a good price on Market.Market). Danish oil is a product manufactured by several companies, which leads to variations in composition. The more tung oil it contains, the better it is, but also the more expensive. Not all varieties of Danish oil are exterior resistant. The combination of the two oils is very good because the linseed oil penetrates very well into the wood (it has a small molecule size), protecting it from the inside, while the tung oil forms a film that keeps water out and does not wash the linseed oil out from the inside. Products with a low percentage of pigments should be used for sun resistance.
Wood burning followed by oiling
Oiling shallow burnt wood is a common method in rural areas. In the past, it was used to protect fences or the planks used to make the fences of the buildings. Unfortunately, the combination of burning with oil has led to the idea of using burnt motor oil to protect the wood, a toxic product which is not recommended. The recommended method is superficial burning of the wood with a gas lamp, followed by brushing and oiling. The purpose of brushing is not to remove the burn completely, but only to remove very fragile areas. Linseed oil is applied after brushing. The resulting wood is highly resistant to both water and sunlight.
In Japan the method has been used for hundreds of years to protect the exterior wood of houses. It's called Shou Sugi Ban and involves a repeated burning of the wood followed by sudden cooling with water. This forms a superficial layer of charcoal which is highly resistant to rotting. Once the desired degree of burning is reached, the wood is oiled. The method is described in detail here.
Synthetic oils
There are a lot of non-natural oils on the market. They are blends of mineral oils and synthetic oils or just synthetic oils. Mineral oils are fractions obtained from the refining of petroleum, while synthetic oils are products/resins obtained from chemical reactions. They are cheaper than natural oils and sometimes have better resistance over time. There are very good quality synthetic oils on the market (Rubio monocoat, Borma Wax) which give the wood a pleasant appearance and good resistance over time.
Tar - wood for wood
This is wood tar, not the residue from oil refining. The latter, which has been used for years to protect wooden railroad tracks, is toxic and carcinogenic. In the past, wood tar has also been produced here as a by-product of beechwood distillation. More commonly found online than in DIY stores, it comes mainly from Nordic countries, but also from the US and Asia.
Wood tar (especially pine tar) protects wood against water, moisture and insects, including termites. It is a thick liquid that must be heated to 60°C before it can be used. Drying is very slow and takes several weeks, depending on air humidity and temperature. It is 100% natural with very good moisture resistance and is also used to protect wooden boats. Information on how to obtain wood tar here.
Water soluble wax - a decent strength alternative
Water-based wax, also known as water-based wax impregnant or water-based wax wax lye, is a product recommended especially for seasonal wooden objects (deckchairs, umbrellas, etc.) Its durability is rarely more than 1-2 years, but it is easy to restore, just like oil. Because it does not film, the old coat does not have to be removed, refinishing is done by applying a new coat.
It is a good choice for finishing exterior wood protected from the weather and the sun, such as arrowwood, wood from covered and side-protected terraces, etc. In these situations it is the best choice, especially as it is not expensive.
Water-based finishing systems
They are systems because they involve several products applied in successive layers, each with its own well-defined role. They are used mainly in workshops and factories, by professionals, but there are also versions adapted for DIY. They are chemical, synthetic products, the base resin being acrylic, polyurethane or a combination. Usually three coats are applied, one for colouring and/or insect/fungal protection, one to ensure very good adhesion to the wood (primer) and one to have surface properties (lacquer/paintSuch systems generally have very good resistance over time provided that the technology is rigorously followed. How such a finish is made is described in detail here.
There are such systems where the manufacturer speaks of 12-15 years of resistance. This is the resistance until the first signs of degradation appear, the first cracks in the film. The main disadvantage of the film-forming systems is refinishing because the film has to be completely removed and the wood sanded the white. It is therefore recommended to prolong the life of the finish with maintenance treatments applied every 3-4 years. They are easy to apply with a cloth or brush or even as a spray.
Lazuri 3 in 1
These are simplified systems aimed mainly at the DIY market. That is, the whole system above is reduced to one product that does all three. It goes without saying that the results are not the same, just trying to simplify the procedure at the expense of film quality and durability. Both water-based and water-based 3-in-1 lacquers are available on the market. oil-based or alkyd.
The advantage is easier application and the disadvantages - low resistance over time (generally 2-4 years) and film build which means difficult reapplication with stripping and/or sanding the surface.
Alkyd varnish/paint - the synthetic version of oil and oil-based paints
Alkyd products are the synthesized version of oil-based products, which are also similar in oily appearance. Their appearance on the market many years ago was a great success because they offered similar protection to linseed oil-based paints at a much lower price. Plus they could be applied to anything - wood, metal, walls, indoors or out. They are film-forming products that must be removed when refinishing, unlike natural oil-based paints.
The exterior resistance of alkyd products is good, but the heavy odor of the solvent (white spirit, petroleum derivative) makes them less widely used than water-based products. And the price is generally lower than for waterborne products.
Pressure impregnation of wood
In the old days it was customary to boil exterior wood (windows, for example) in linseed oil for better durability. The high temperature made the oil thinner, and boiling removed the water from the wood, replacing it with oil. It was a way of impregnating the wood. The disadvantage was that the oil would expand on hot summer days and the windows would start to cry, i.e. oil drips from them, often damaging the facade of the house.
Impregnation is now done under vacuum or pressure and products are used that increase the wood's resistance to the outdoors without the risk of the wood coming out when the pressure stops. This type of wood is recommended for decks and facades as its strength is very good. It is a finishable wood, but its degradation in the absence of a finish is much less. Find more information about impregnation here.
The strength of wood is also increased by treatments that alter its composition or density. About Accoya, acetylated wood or Kebony, wood guaranteed to last 30 years outdoors maintenance-free I have already written. But in these cases the resistance comes from complicated treatments, not the finish.
In conclusion
If you want a natural finish, use linseed or tung oil or products based on these oils. Check the label to see if there are any chemical additives. Respect the way of working, the number of coats and the waiting time between coats. Refinish when the wood is dry, i.e. the shiny look of the oil is gone.
High-strength finishes are those given by professional systems with successive coats. To achieve that durability, the technology must be followed to the letter. Waterborne materials have good resistance and recently products have also been developed that are more environmentally and human health friendly. To prolong its life, the finish must be maintained. When refinishing it is mandatory to remove the old coating completely and start with clean wood.
I hope to have covered all the systems that are now on the market. I promise to complete the material if there is any news. I also hope you find the material useful. And if you have any questions or queries, leave them below in the dedicated space. I will certainly reply.
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Hello. I have purchased a pine garden fence that the seller mentions is also treated but does not mention with and for what. The wood is in natural colour and I want to paint it white. I have a matt paint based on alkyd resins (kober opal) and I want to know if I need to apply other products before or after painting, for example linseed oil or wood primer..... If yes, what would be the order? Thanks
Hello!
If it's outdoor wood, the treatment could be insect-fungicide, which is helpful. Linseed oil is not needed, and primer is only necessary if the manufacturer (Kober) recommends it (you can download the datasheet from the company's website). Otherwise, two coats of paint are sufficient.
However, it is good to ask what that treatment consists of so as not to have problems of incompatibility between layers. This means that a layer of material (e.g. a thin coat of water-based primer, which is sometimes used) has not been applied that is not compatible with the alkyd paint.
All the best!
Hello.
I have a fence and two pine balconies installed in 2019. They were then machined and coated with a water-based varnish by the manufacturer (don't know details).
In the meantime we have not done any maintenance and now some of the boards have cracked, in some areas the varnish film has peeled off and the appearance is not at all pleasant.
What solutions do you recommend, both in terms of the product to be used and the method of application?
Thank you.
Good evening!
I would use outdoor oil. The big advantage is that it doesn't form a film and doesn't run off. Over time it is "washed" by the rain, and when the wood becomes dry looking (oiled wood looks wet) another coat of oil is applied without removing the old coat.
Because you have cracked boards and peeling varnish, all the wood needs to be sanded and the old varnish removed, no matter what solutions you apply next. If it is not removed, it will fall off over time along with what is applied on top and you are working for nothing. Once you get to clean wood, apply 2 coats of oil-based exterior varnish. Kreidezeit products have good resistance and if properly applied will last 4-5 years without maintenance. Kreidezeit pre-coloured varnish, with description and application instructions, find here.
Apply with a brush or solvent-resistant roller brush. It can also be applied with a spray gun, but the dilution must be increased and material losses are higher.
You can also find information about the Kredezeit lakes in the link below.
https://revistadinlemn.ro/2020/07/02/lazuri-kreidezeit-pe-baza-de-ulei-pentru-finisaj-exterior-natural-si-rezistent/
Hello. I follow the articles in your magazine, including this article you refer to. I would like, however, in particular, to know your opinion regarding the protection of some oak shutters from humidity and especially from UV rays. I have tried ICA's impregnator and their best water based varnish, but the result was that after more than a year, on horizontal surfaces exposed to the sun's rays, the varnish exfoliated and the colour of the wood became almost black. From what I gather, your preference would be oils, but what kind of oils do you recommend? Also, do oil based paints fall into the same category? Thanks in advance.
Hello!
Thanks for following us!
Indeed, I prefer the oil and recommend it especially because it is easy to apply and maintain. Professional products, such as ICA brand products, have stricter application criteria and achieve high performance, especially when applied in factories using well-developed technologies. Below is an example of such a window finish with ICA products.
In the case of the shutters, the water certainly did not drain well in the horizontal areas and accelerated the peeling of the varnish. The almost black colour that has appeared is due to mould that has set in and is favoured by the increased humidity. The wood changes colour under UV light, but the resulting colour is bluish grey, not black. Clean the black areas with anti-mould products because there is a danger of the wood rotting. You can use chlorine-based bleach. Sodium hypochlorite is an enemy of mould.
Black colour on oak can also occur due to tannin in the oak in contact with water and metal. In the case of water-based finishes, it is recommended to first apply an insulating coating that locks the tannin inside.
The oils I prefer to work with are tung oil, Danish oil and Kreidezeit lazines (links at the end). They are materials that protect well and "tell" you when you need to refinish. Over time the wood loses that oil sheen that makes it look wet and takes on a dry look. This is a signal that another coat of oil needs to be applied. Oils used outdoors should have a small percentage of pigment to resist UV rays. Totally transparent oils are not recommended.
Oil-based paints fall into the same category as oils, being even more resistant over time because of their higher pigment content. A synthetic variant of these paints is alkyd paint. It behaves in the same way, but instead of linseed oil it contains mineral oils (obtained by processing petroleum) and even synthetic oils.
Following the manufacturer's application instructions, drying times or sanding methods are just as important as the product itself. Sometimes the low resistance of finishes is due to application mistakes and not the products, which we end up blaming.
I hope this has been helpful.
All the best!
https://www.youtube.com/watch?v=Rk2uolQmOac&t=52s
https://revistadinlemn.ro/2020/06/10/uleiul-de-tung-uleiul-pentru-lemn-care-face-pelicula-si-rezista-foarte-bine-la-umezeala/
https://revistadinlemn.ro/2020/07/02/lazuri-kreidezeit-pe-baza-de-ulei-pentru-finisaj-exterior-natural-si-rezistent/
https://revistadinlemn.ro/2018/01/15/danish-oil-ulei-finisare-lemn/
Hello,
Thank you very much for your prompt reply. In the meantime I have found out and reached out to those who market Sikkens lacquers. Without advertising, I understand that it is also an oil based product and would like to try it. The only dilemma I have is that on the one hand I have holsters that have already been treated with ICA, which I will have to clean again, and on the other hand I have shutter hoops re-done from scratch, where there will definitely be differences in shades.
I'll run some tests.
I was recommended to use sikkens cetol hls plus. Do you know of these products and have you formed an opinion?
Thank you,
Adrian
Correction, Sikkens are solvent based, not actually oils.
Hello!
Sikkens is a good brand. The varnish is an alkyd varnish, on the same basis as the alkyd paints I mentioned. To use it you have to clean the water based varnish you used very well because they don't get along. Applied over areas where the old film still exists, it will crack.
For a good result follow the technology exactly. Sikkens is also a professional brand, like ICA.
Good luck!
Dear Madam Engineer,
In the immediate future we will be rebuilding the wooden fence of the country property with a completely new one. The fence will also be made of wood (about 70 m long). We are under pressure to complete it as soon as possible and in researching how to treat the wood to make it more resistant to environmental factors, we realised that we had not considered a number of very important issues. I digress to thank and congratulate you for the extremely useful and interesting articles, without which it would have been almost impossible for me to learn so much information in such a short time!
Coming back to our situation, we have already ordered the lumber for the hawthorns (fir wood), but we did not take into account that the wood is not dried and not planed. For the support and strength elements (posts and leaks), we used yard willow, but all the felling was done this summer.
Under these conditions (wet wood), what could we do to increase the strength of the fence? I would like to know if uluca should be planed and if it would help to burn it superficially, followed by treating it with linseed oil (boiled or spiked), as much as will be absorbed, following the steps described in the article. Can we hope that after a year in the open air (but also exposed to the weather, unfortunately), the wood will dry out and be treated with wood stain (e.g. Kreidezeit) the following summer/autumn?
Regarding the posts, the ends that will go into the ground will be burned, but I would like to know if burning them can also be done with a gas burner (with a bottle) or if a slightly deeper burn is needed (if it is more efficient to keep them in the fire). I would also like to know if it would help/make sense to burn them all the way through, also for increased moisture resistance.
Thank you in advance for your support and time and any additional tips or suggestions are welcome!
Hello!
Thanks for your appreciation!
Indeed, it was better if the wood was cut in winter, but being used outside, the consequences will not be as significant as if you had used it inside.
You've chosen your wood well. Acacia is very tough and hard on the outside. And fir, and softwoods in general, behave well.
Problems that can occur are cracks in the acacia posts, cracks in the ends of the planks and warping of the planks. To limit leakage it is good to protect the ends of the fibre (the area cut perpendicular to the ends of the posts and planks) with a solution of paraffin, aracite dissolved in water (1:3-1:4 with water) or diluted primer. This will cause the water to come out of the wood more slowly, no more tension and the wood will not crack. As the planks will be fitted, the warping will be negligible and limited by the grip. Over time there may be play in the planks due to shrinkage caused by water loss.
Planing has the advantage of reducing absorption, which is good for wood used outdoors. The rougher it is, the greater the absorption and the more noticeable the swelling and shrinkage. So yes, if you have the opportunity plank the uluca.
Burning is a very good solution that increases the strength of wood outdoors. Shou Sugi Ban is a popular Japanese method of protecting wood outdoors. It is described in detail in the link at the end. The deeper the burn the better. After burning and brushing linseed oil is applied. You can come back after a year, even 2, when the wood is drier, with another 2 coats of linseed oil or you can apply the colourless Kreidezeit. There is no need for coloured varnish because the wood already has black pigment (carbon black) from burning. Kreidezeit is superior to linseed oil because it is a mixture of linseed oil and tung oil. So is Danish oil. Tung oil is very resistant on the outside.
Burning can be done with a burner along the entire length of the wood.
Below are some links that may be of use to you.
Good luck!
https://revistadinlemn.ro/2017/06/27/arderea-lemnului-de-la-protectie-la-colorare/
https://revistadinlemn.ro/2020/06/10/uleiul-de-tung-uleiul-pentru-lemn-care-face-pelicula-si-rezista-foarte-bine-la-umezeala/
https://revistadinlemn.ro/2022/08/11/de-ce-nu-se-folosesc-lacuri-si-uleiuri-transparente-pentru-protejarea-lemnului-aflat-la-exterior/
https://revistadinlemn.ro/2019/06/12/cele-mai-rezistente-specii-de-lemn-la-exterior/
https://revistadinlemn.ro/2018/08/03/12-reguli-simple-pentru-a-avea-constructii-din-lemn-rezistente-la-exterior/
https://revistadinlemn.ro/2020/04/30/de-ce-gardul-facut-de-bunicul-meu-a-durat-50-de-ani/
Hello! I have given the oak parquet with rubiomonocoat oil, but I can't find anywhere if I could apply it again, it seems to me that the wood has absorbed everything and has no sheen at all. Shall I give the oil one more time? Thanks for any clarification.
Hello!
I didn't work with Rubio Monocoat. From what I've read and seen on the net, you apply one coat, in excess, let the wood absorb the required amount, then wipe off the excess To gloss, buff.
Another layer no longer clings to the old layer. If you read the materials on scratch repair, you will see that the oil only adheres to the wood where the old layer was removed (scratch, sanding). On the existing oil layer, the newly applied oil can be wiped off without affecting the appearance in any way.
My opinion is that you should not give another coat but just polish the one already applied. A new coat would only catch on if the wood could still absorb it.
I also recommend that you seek advice from Rubio Monocoat representatives.
All the best!
Hello,
I start by saying that I have read a lot of your material, and thank you for providing the most detailed and complete information.
About me I can say that I discovered that I love woodworking a year ago when I built a wooden hanging house for my little girl. During the work I also bought various power tools I needed.
Now I have a new challenge, I have a house under construction and by the end of the year it has to be finished in red, including the roofing. It is on two levels, and the whole back side has two overlapping terraces of 25sqm each. As we like wood, we want to make the balustrades out of wood. The top will be made of wood including the four supporting posts of the gable roof. The terrace on the ground floor has reinforced concrete pillars, the floor between the two terraces is also concrete.
The four posts on the first floor will be made of 15x15cm dried pine laminated timber. The rest of the wood, i.e. the beams and trusses that will remain visible (above the terrace upstairs), will be green fir wood bought a week ago. Of course, they will all be pulled to the hearse by the builder, prior to erection.
I will finish the apparent siding on the right side of the terrace, it will be made of 15cm wide pine wood which I will pull to thickness and I will saw it. This planking was bought a month ago and has been left to dry, with a sip between each row.
I'm not going to fit the railings now. I'll still buy pine lumber that I'll let dry for at least a year, then I'll process and sand it myself.
The house is on a hill, the side with the terraces is on the East, exactly from the direction from which some very strong winds blow. The final wood finish will be transparent, probably something to imitate a light oak.
The problem I'm running into now is that I need to protect the wood for about 2 years when I continue with finishing the house. I'd rather not let it turn grey like that and then have to sand it again.
From what I have read so far from your materials, it would be good to use either Danuish Oil or Kreidezeit lazura. Possibly give it a first coat this year with a clear varnish that also allows the wood to dry without risk of peeling. I would have liked to use varnishes that you can find on all roads (it would be a cheaper option for me), alkyd or water-based. But I'm thinking that if the wood is not dry yet, everything I apply now will crack next year when the wood dries.
I would ask you, when you have time, to give me one or more options/products for my case.
Thank you very much!
Hello!
Thanks for your appreciation!
To protect the wood for a short period the best option is oil. And to prevent the wood from turning grey and having to be sanded, the oil should contain a small amount of pigment. The appearance will be semi-transparent.
I would use Kreidezeit lard. As you don't know when you're going to refinish, it's risky to use pigmented linseed oil that the rains can "wash off" in 6 months. The varnish is more resistant because it is a mixture of linseed and tung oil, but it is better if the wood is dry as much as possible because otherwise it absorbs a little and will be easier to remove. You can leave just one coat. You will see when the rains remove it because the wood loses its oily sheen and becomes dry. If you don't apply another coat to protect it, the colour of the wood will gradually start to change to a bluish grey.
My recommendation is to use wood as dry as possible (max.18-20% moisture content). Green wood works quite hard, especially fir, and warping, cracking and shrinkage can occur.
Good luck!
Thanks a lot for the tips!
I would like to proceed as follows, if this is correct:
-apply bait to highlight the wood pattern, and hope to find a similar shade to beech wood.
-I apply boiled linseed oil or spicy oil for moisture protection until I can apply the final coat.
-in a year's time I will apply either Kreidezeit's colourless lye or Borma wachs' Decking Oil HD (Danish Oil).
If you can tell me:
1. would bathing be enough for UV protection?
2. The Sicativated linseed oil, I am not sure if it makes the film stiff, or if it allows the subsequent application of Kreidezeit lacquer, or HD Decking oil?
3. Would it be better to combine the linseed oil with some pigment, and not apply the bath?
Sincerely,
Adrian
Good evening!
1. To be sufficient the bath must be specially designed for outdoor use and be UV resistant.
2. You can apply Kreidezeit or Danish oil over the top of the spicy/hot linseed oil.
3. Oil combined with pigment is more resistant than bath. But don't forget that linseed oil is washed away quite quickly by the elements, especially if it's a rainy area. Try refinishing after a year or when you see that the wood is getting dry and the pigmented oil seems to be gone.
Good luck!
Hello, I have a question too, someone advised me to give the burnt oil asterial to the house.
My question is how it can affect me or if it's good
Thank you
Good evening!
Not a good recommendation. Burnt motor oil is toxic, dangerous to health. I've heard of such recommendations being made just because people don't know what problems they may have. I just see it as oil that is a shame to throw away. But it is full of compounds resulting from combustion, with very high carcinogenic potential.
You can use boiled or dried linseed oil, which you can find in any DIY store at a decent price.
Good luck!