This will be the wood after 20 weeks

If you consider untreated wood on your house, there are some things you need to take care of.

This will be the wood after 20 weeks


Untreated wood is modern, you do not need to paint your house – assuming you like the wood crying. Patina, says the architects, and emphasizes the charm of natural aging of the materials.

Architects office Poulsson / Pran uses some untreated wood in their projects.

– We use it because properly chosen, it reduces climate stress, and it provides less maintenance. In addition, we like the aesthetics – the panel is patinated and shows aging in a good way, says architect Andreas Poulsson, general manager of Poulsson / Pran.

Untreated, Norwegian wood materials are furthermore the most environmentally friendly clothing, according to a report from the Norwegian Institute of Wood Technology.

But why is untreated, yellowish pine, or coffee brown Kebony, gray with time?

The answer sounds scumier than it is: Swallow soup – a type of mildew.

Head of Department for Building Materials and Structures at SINTEF, Petra Rüther has written a doctoral dissertation on how different tree species develop. She denies that molds are creepy things.

– It’s quite normal. One must distinguish between mold and herb, she emphasizes.

The mildew comes from substances that are in the cavities of the wood and do not affect the structure of the tree. The rat top, however, eats substances that break down the wood itself.

This will be the wood after 20 weeks

ELDES: After one, four, eight and twenty weeks, untreated wood looks like this Photo: Mycoteam

This will be the wood after 20 weeks

DIFFERENT COLORS: Single-family house in a pinewood pine on the winner, designed by the architect office Poulsson / Pran. The color of the wood is somewhat different under the roof and where the wall is more exposed to weather. Photo: Jonas Adolfsen

Cupcake gives gray wall

And now comes the complementary explanation of what’s happening:

– There are two things that affect the surface: moisture and sunlight, says Rüther.

UV rays from the sun break down the substance lignin, which is the link between the cellulose fibers in the tree. Lignin is not really water-soluble, but with UV rays it is converted to a substance that is washed out of rainwater. When lignin disappears, the cellulose fibers are left loose on the surface of the shelf. Cellulose fibers have a white or silvery color.

If the moisture and temperature conditions are correct, the mildew will come. Mushrooms grow on the surface in places there is enough access to moisture – but not very moist, and not very dry.

– Without fungus the façade would become more silver gray. You see it where it’s very dry. Up in height, the wood is often dark because the sun is so strong that the surface is burned. Then looks look a bit different, says the research director.

You also see the difference between untreated wood that is underneath a roof rack or a wall under a balcony that is protected from rain.

– It’s so dry that the fungus does not grow, the wood looks new.

How to get gray house faster

This will be the wood after 20 weeks

SMALL DIFFERENTS: Different types of wood and treatments before (up) and after 3.5 years of climate exposure (down) outdoors to west. Photo: Petra Rüther, SINTEF Building Research

This will be the wood after 20 weeks

MUGSOPP: On this shelf the spring water is eroded, loose cellulose fibers lie on the surface and have become gray of mildew. Photo: Petra Rüther, SINTEF Building Research.

Someone appreciates the gray aging of the wood that they want to speed up the process. Then they can treat the wall with an iron and white solution. After a short time it will give a gray to silver gray surface.

– Unlike the appearance of an untreated wall that has been exposed to wind and weather for some years, says Sissel Bjørge, researcher at the Norwegian Institute of Wood Technology.

At the Norwegian Institute of Tritonics, researchers have tested the difference between untreated wood and wood treated with iron vitriol. That the process goes faster, there is no doubt, but there are some things to think about whether you use iron vitriol.

– It’s important to remember that iron vitriol does not provide any protection against moisture penetration and scratch like paint or stain will do, “says Bjørge..

In addition, a wall treated with iron vitriol after a short period of time will be a bad surface for a stain, cover or paint because the outer wood fibers in the wood surface will be broken down.

When the wood stands out in weather, not only will the color change. The fibers also erode, wipe away from the wind, the wood gets increased roughness, and the surface may break up as the wood is moistened and wiped out. It may sound violent, but Rüther is calm. The changes only occur in the approximately 0.08 outer millimeters of the surface. It’s so thin that you can scrape it away with your nail.

– Untreated wood erodes approximately five millimeters in 100 years. A typical dressing table is 20 mm, it takes about 400 years before it disappears, she says.

By the way, it is important that the raw bush develops in untreated wood.

– If there is no water at the bottom, there will be no rash. Neither in a well detailed facade, says Rüther.

Beware how to build

Rüther advises people who consider untreated wood on their houses to be aware that anything that protrudes from the surface or enters affects the appearance.

This will be the wood after 20 weeks

SEE THE DIFFERENCE: Untreated Osp cladding, from a chapel in Trondheim. The window on the right is covered, while the wall is otherwise exposed to wind and weather. Photo: Petra Rüther, SINTEF Building Research.

– A small windscreen, or a drop tube, or a corner that is more exposed to rain, often destroys appearance. Many people feel bad if color change occurs very unevenly.

She does not think there are big differences in the woods when it comes to the speed of color change. Over time, all planks are gray.

– If the wood is going to last for 20 years, it does not play a role for one and a half years, she says.

So-called kernel kernel (from the center, inside the log) should contain some substances that make it more resistant to fungi generally, including mold. You can also choose to treat the garment with fungicides, so that the fungus will come later or less, but Rüther will not recommend it.

– It will come eventually anyway. If you have an untreated triangle, you should accept what’s happening, she thinks.

– How to make the dream home of a weary refurbishment object?

– Five kitchens before and after


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