Wondering How to Preserve Wood; by Aker Woods
We want your wood to last forever, and yes, you can make wood last forever.
The photo to the right is of a wooden chapel, called a Stavkirke, in Oye, Norway. It was built in 1327. Furthermore, it has survived the very wet Norwegian climate. And it's not built from a particularly rot-resistant wood. It's pine. And those medieval Norwegians didn't have access to industrial pressure treaters. So why did their wood last so much longer? What's the secret?
First, there's no such thing as rot-proof wood. All woods rot under the right conditions. Pressure-treated wood rots, redwood rots, and cedar rots.
Consider these recommendations for making your wood last:
Use linseed or tung oil, or a product based on one of these. Some wood preservatives are water-based. They coat the wood with a wax-like film that beads water. This looks impressive, but after a few years, the film starts to crack and peel. At this point, it can actually hold water against the wood and promote rot. Another problem with these preservatives is that as the film ages, it discolors and hides some of the beauty of the wood grain. Finally, water-based preservatives make it hard for the wood to absorb a good oil after you realize that's what you should be using.
Oil as needed. Wood can only absorb a certain amount of oil at a time, and oiling is not a once-in-a-lifetime event. If your oil starts to form crystals on the surface of the wood, you've used too much. You haven't hurt anything, but you've wasted your oil. Different sides of a structure will need to be oiled more frequently. Here in the Black Hills, the North and West sides of buildings always need re-oiled sooner than the other two because the prevailing winds pelt those sides with snow and rain more frequently. Your wood needs another coat of oil if it feels and looks dry. After about 2 or 3 oilings, your wood will usually not need more oil for a decade or two.
Don't pile snow against wood. If you leave snow on a deck made of pressure-treated wood or a rot-resistant wood like cedar, it will rot faster than an un-treated pine deck that gets shoveled.
Vertical boards resist rot. Notice the Oye Stavkirke. All the boards are vertical. When water hits them, it runs down the walls and escapes, rather than coming to rest between two horizontal boards.
Build on stone or cement foundations rather than burying support posts in the ground. The wood in the Oye Stavkirke never touches the ground.
Don't allow firewood, building materials, furniture, or vegetation next to wood. The Oye Stavkirke provides another good lesson here. All the wood is benefiting from the free flow of air. This air flow keeps humidity levels from building up next to the wood.
Consider covered porches and oversized eaves on wood structures. The less wood is exposed to moisture and sunlight, the better.
Build on high, well-drained ground. Notice that the Oye Stavkirke is built on a small knoll. After heavy rains, the humidity declines more quickly than it would in an area with standing water.
Keep humidity low on the inside of the building. Modern building methods have made a fetish of energy efficiency. Windows and doors are air-tight, new homes are wrapped in a blanket of plastic before they're sided, and there's caulking in every single nook and cranny. Some homeowners put a temporary layer of plastic film over their windows all winter long. Try to strike a balance. With all the cooking and hot showers occurring in modern homes, humidity levels can get unnaturally high if you don't let a little air in. Open a window on warm winter days. Leave a few small cracks alone. You'll not only have lower humidity, you'll have fresher air and a lower chance of dangerous buildups of radon gas.
If you do put a wood post in the ground, don't pour concrete around it. The concrete forms a water barrier that holds moisture against the wood. Coat all wood in the ground with roof cement, and fill the area around it and under it with large rocks.