There are two types of wood rot, and the names can be misleading since moisture is an underlying factor with both.
The two types are wet and dry rot, but don’t let the name “dry” mislead you, they’re both caused by fungi growing on wet wood, it’s just a matter of percentage of moisture that separates the two from growing.
So how do you stop wood rot from spreading and how do you treat rotting wood?
In this post, I’ll explain why wood rot occurs, how to treat wood rot, and some tips to prevent future rot. Let’s dig in!
- To stop wood rot from spreading it’s best to treat the wood beforehand, limit water and moisture to the wood, be sure there is proper air circulation around the area, and use a wood filler to fill the existing rotted wood.
- Some climates are more prone to wet rot because of the excess humidity.
- Preventing rotten wood in the first place is the best way to stop wood rot from spreading to surrounding wood.
Why Does Wood Rot?
Wood rot is the result of fungal growth that occurs when the wood is either saturated with water or is in an area without proper ventilation.
Wet rot is common in humid regions where it rains or snows often.
The constant exposure to water allows fungus to take hold and begin devouring the wood over time. It is a slower process than termites can bring, but it will eventually have the same effect with weakened or collapsed wood structures placing buildings, and people at risk.
Wet rot has a spongy feel to it. It makes wood soft to the touch and easy to compress. In advanced stages, you can even squeeze water out of the wood. It is often black due to the heavy fungus content.
Dry rot starts most often as cracks in the wood, doesn’t hold water, and feels spongy like wet rot does, but can become crumbly. When the crumbling is advanced, you can flake off sections of dry rotted wood with your fingernail.
Both wet and dry rot are natural processes that nature uses to decompose fallen limbs, trees, and exposed stumps. In the wild, it’s a great habitat for insects and grubs to live in and feed on – but not so great for your home or outdoor projects.
Climate is a huge factor in the rate that wood rots.
I once had to remove a fence post that my grandfather set in 1938 that was part of the original boundary fence of our now home. I wrapped a chain around the post, hooked a “Handyman” jack under the chain, and pulled the post out of the ground.
The post was stained below ground level, but was as solid as the day he tamped it into the ground 85 years ago.
The secret is our arid Wyoming climate. The post was exposed, but humidity rarely exceeds 25 percent in the high desert we call home. The post was also located on a ridge, so no runoff water ever hit it.
In other areas or climates, this post would likely be long gone from wood rot, and couldn’t hold up any rails.
Ways to Stop Wood from Rotting
Rot, no matter what the type is costly, can be dangerous, and is something to be vigilant about – but there are effective ways to prevent it from happening and steps you can take to mitigate it when it does.
1. Treat the Wood
Prevention is always the best cure, and that’s true with wood rot. You have a couple of options when it comes to treating wood to prevent wood rot. The first is to buy pressure-treated wood, buy water-resistant wood, or treat lumber yourself.
Pressure Treated Lumber
With new construction, it’s always best to pay a little more for pressure-treated lumber if there is a chance that it can come in contact with water, or if it will be in a poorly ventilated area where moisture is high and constant.
Dimensional pressure-treated lumber will have puncture grooves on the main surface of the boards where a combination of fungicide/wood preservative has been injected into the wood and it’s easy to identify. Pressure-treated lumber often has a greenish tint and you’ll pay more for it than standard pine, spruce, fir, or hemlock.
Water Resistant Wood
Pressure-treated wood is a great option, but it can’t compete with the quality and durability of naturally water-resistant wood.
Many species of trees provide excellent lumber with a high level of water resistance that prevents rot from getting a foothold, but only a couple are economically feasible to use in North America.
Redwood and cypress are the two most commonly used construction-grade lumber with high rot and water resistance.
Redwood is predominant in the west, and cypress in the American southeast where it is a common large tree that grows in swampy areas. Cypress is the harder, denser of the two, but redwood, with its high tannin levels, can protect a foundation or remain solid on a deck for decades in even the wettest of climates.
A third species, cottonwood, was used for paddles on riverboats in the 19th century and remains as a wood used to build water-resistant pallets. The heavy, almost hairy, exposed fibers and difficulty of cutting the huge, sand-imbedded trunks make it less viable than cypress or redwood.
2. Avoid Water Around Wood
In the same prevention venue, dry wood won’t rot, and wood stays dry if you keep water away from it.
Planning and using the landscape to your advantage can keep the water away while protecting your untreated wood.
Water working its way into a home along the foundation is the most common way that rot gets a foothold.
To prevent this, you can waterproof a concrete foundation with a coating of foundation tar, or you can install a French drain around the perimeter of your home to prevent water from leaking through the foundation walls.
A French drain is just a line of perforated four, six, or eight-inch PVC pipe laid in a bed of gravel at the base of a foundation. As the water flows with gravity, it hits the perforations and flows away from the house. This is an inexpensive way to prevent future wood rot damage in the construction phase.
Dikes, ditches, rubberized coatings, metal flashing, and building above the water level are also excellent methods of diverting or preventing water from hitting your foundation.
Here’s how to build a French drain:
- Survey the area before the initial groundwork
- Use shovels, picks, and heavy equipment to lay a gravel base for the French drain
- Lay perforated pipe in gravel with ¼ inch drop over four feet for drainage
- Use a shovel or heavy equipment to create a water barrier to divert flow
- Use a heavy brush or broom to coat concrete walls/foundation with tar
3. Keep the Area Well Ventilated
Ventilation is an important part of a home, from the basement floor to the peak of the roof above, and all can work together to prevent rot from taking hold.
Most assume that rot occurs on the bottom of posts, along bottom sill plates, and along the lowest portion of a home. While that is the major area where rot can damage a home, it can also compromise a roof, even a watertight roof if proper ventilation is not in place.
Roof vents, properly installed to prevent seepage during rain and snow allow good ventilation as does a good vent along the peak of a roof. If wind is prevalent in your area, proper ventilation be even easier to maintain. If your home is in an area of primarily calm conditions, a powered vent can solve humidity issues by pulling air out of one end of a roof and drawing it in through a slatted opening on the other. This natural flow of air keeps humidity at bay and the constant flow of clean air prevents fungus from getting a grip and producing wood rot.
The same is true for crawl spaces and basements, they must be well-ventilated.
Often you can tell if ventilation is poor by just smelling the area when you enter it. That musty smell, slightly wet odor found in basements and crawl spaces is the smell of humidity, and if it’s profound, it is the smell of fungi growing in those damp areas.
Check out these ways to keep wood from splitting or cracking!
4. Fill Rotted Wood with Wood Filler
After the fact actions are never as good as prevention, but if you discover rot, there are still many things you can do to keep it from spreading and even bring the wood back to near-new condition.
Wood filler is one fix that, if done properly, can restore wood to a stronger condition than the rot has created.
While it won’t ever be as good as the original, pristine lumber, but it can prevent further rot, and with modern epoxy-style fillers, it can create a bond that ties the rotted wood fibers back together with structural integrity. A wood filler with included fungicide will repair the damage and prevent further fungi from growing.
Here’s how to use wood filler to treat wood rot:
- Locate affected wood
- Clean out all rot with a wire brush putty knife or screwdriver. If necessary use a hammer and chisel to create a new clean area, devoid of rot for the filler to bond to.
- Pack the damaged area with filler. If the area is large or deep, lay down a thin coat, allow it to dry then add additional coats until the patched area is flush with the existing lumber.
5. Apply a Preservative
Generations ago, creosote was the preservative used for everything from pylons to railroad ties and even the foundation supports of homes. Creosote is now a known carcinogen and is no longer used as a preservative.
You can see its effectiveness if you take a look at an aging railroad tie, wood rot didn’t have a chance. The good news is that there are wide varieties of chemical preservatives you can apply that have good, long-lasting effects in the war against wood rot.
They even have a few latex-based preservatives, though the most people still primarily rely on oil-based products.
Here’s how to use a wood preservative to prevent rot:
- Apply the preservative to the lumber
- Use a brush, roller, or spray gun to cover all surfaces.
- Let the preservative dry
- Follow the manufacturer’s guidelines and apply as many coats as indicated.
You can also use bleach to stop wood rot if you’re still having trouble.
Final Thoughts on Preventing Wood Rot from Spreading
Wood rot happens, and it can happen anywhere.
Vigilance on your part is the best defense in preventing rot from starting, and in removing it effectively once you find it.
Both wet rot and dry rot are caused by wood destroying fungus and can quickly become a serious issue.
To stop wood rot from spreading, your best bet is to be sure that there is no excess moisture around your wood. You should also aim to keep the area ventilated to keep the humidity low.
Randy grew up on a ranch in central Wyoming. At an early age he learned that if you didn’t do things yourself, no one else was going to do it for you. He worked in sawmills, on heavy construction jobs, and learned to pour concrete, tie iron, weld, and operate heavy equipment during his summers in high school and college.
As a teacher and coach, he augmented his income running summer construction businesses with fellow teachers. In rural Wyoming, you don’t need a trade license to work on your own projects, so he learned electrical, plumbing, earthwork, and finish carpentry. He is also an accomplished DIY writer, producing a wide variety of content found on publications like ManMadeDIY and others.