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How to Tell if Wood is Rotten

Rotting wood is a common woodworking and construction challenge. It discolors furniture and other woodworking pieces, weakens structures, and can cause unbearable musty smells.

Worse still, rotten furniture and structures can cause various health issues, including irritation and rashes.

We’ve developed this guide to help you how to tell if wood is rotten and apply proper remedies to mitigate the problem.

In addition, the guide provides several practical tips to prevent wood rotting.

How to Tell if Wood is Rotten

The most common signs of rotten wood include; Discoloration, shrunken size, cracks, splintering, damp musty smell, softness to the touch, grey-whitish skin and yellow lilac patches.

What is Wood Rot?

Wood rot is damage to wooden boards and surfaces caused by various fungi. These fungi (living microorganisms) extend hyphae into the wood substrate to absorb water and nutrients.

Eventually, the wooden structure softens, weakens, changes color, and ultimately decays. The process is triggered by moisture and fungi on the wood surface or deep within the cell structure.

Unfortunately, both elements occur naturally in the atmosphere. For instance, the air around us comprises between 0.1% and 2% moisture, with an average of 0.4%. Meanwhile, there are more than five million fungi in the air and soil around us.

Naturally, fungi only begin to live in wooden boards and structures when the wood’s moisture content rises beyond 20%.

Unfortunately, this means any water spills, rains, and highly humid days increase the risk of fungi attack and subsequent rotting. The same applies in poorly dried wood or porous species that readily absorb moisture.

The fungi consume cellulose fibers (which typically support plant cell walls), leaving the affected section soft and weak. The longer the wet conditions remain, the greater the rotting risk.

Why Should you be Worried?

You should be worried because a dry rot outbreak degrades wood, eventually causing decay. As we’ve seen, rot primarily attacks cellulose, the polymer that gives wood its structural strength.

It releases a chemical known as cellulase that pre-digests cellulose. This has three main impacts on wood;

It weakens the wood

The diminishing cellulose levels cause the wood to lose strength. Unfortunately, weaker wood boards and structures cannot support the original load. Therefore, load-supporting structures crumble, and weight-bearing joints give way.

It blemishes wood

Rotted wood sections are either darker or lighter than the original wood surface. This can diminish the item’s aesthetic qualities, especially furniture and cabinets that we partly adore for their appearance.

Health and safety issues

Finally, rotten furniture and wooden structures pose various health and safety risks.

For instance, prolonged exposure to rotten items increases the risk of blastomycosis, a condition that begins in the lungs and spreads to other body parts, like the skin, bones, and joints.

In addition, rotting wood can cause skin rashes, eye irritation, headaches, and exhaustion.

Types of Wood Rot

There are two main types of wood rot – dry rot and wet rot. You may also come across the terms “brown rot” and “soft rot.” However, these are merely variations of dry or wet rot.

Dry Rot Causes, Signs, and Remedies

What is Dry Rot?

Dry rot is a fungus species known as Serpula Lacrymans. It’s called so because the fungus can attack apparently dry wood and spread without visible dampness.

This is possible because Serpula Lacrymans fungi transport water through cords in the affected wood. The property allows dry rot fungi to attack all types of wood, dry or wet.

Dry rot fungi primarily feed on woodland timber. However, you can also find them in building structures and boats. It mainly attacks the wood’s cellulose, giving the damaged section a brown color.

What Causes Dry Rot on Wood?

Dry rot mainly results from damp conditions. Remember that there are billions of fungi naturally floating in the air.

These fungi settle and create colonies whenever they come across a hospitable environment. Unfortunately, any wood piece with moisture levels above 20% provides the perfect conditions for dry fungi growth.

Once it attacks damp wood sections, dry rot easily spreads to dry sections by transporting moisture to new areas as it expands its colony.

Does Dry Rot Spread?

Yes, dry rot spreads. Indeed, dry rot spreads much more easily than wet rot because it doesn’t require a moisture source to breed.

Instead, dry rot fungi transport moisture from one location to another. This phenomenon allows dry rot fungi to attack completely dry wood surfaces.

It mainly spreads by air. The microscopic spores floating in the air are constantly deposited on new surfaces where the fungi start new colonies. Alternatively, dry rot spores can spread through carpets, fabrics, masonry, and other items.

Stages of Dry Rot

Dry rot has four stages in its life cycle. The cycle begins with spores, which morph into hyphae, then mycelium, and finally, sporophores that produce new spores.

  1. Spores: Dry rot spores are everpresent in indoor air. However, they remain inactive until they come in contact with sufficiently damp wood. About 20% wood moisture is enough to activate the spores. Once they attack wood, they develop into hyphae.
  2. Hyphae: Hyphae are long, branched fungi structures identifiable by fine, white stringy strands found inside the timber and on the exterior surfaces. Dry rots develop fastest at this stage.
  3. Mycelium: Mycelliums are thick masses of hyphae colonies. It’s the stage when most people notice dry rot attacks because the colonies spread uncontrollably, seeking new timber to feed on. A mycelium colony can span a few inches to an entire wood structure.
  4. Sporophores: Sporophores are the fruiting bodies of dry rot. At this stage, the dry rot looks like a mushroom and releases into the air millions of new dry rot spores. Strangely, dry rot fungi primarily form sporophores when they detect habitable changes, such as diminishing food reserves. So, the colony generates and releases new spores to preserve its “generation.” The spores can travel many kilometers seeking new habitat. Then the lifecycle starts all over.

Types of Dry Rot

There is only one species of dry rot – Serpula Lacrymans. All the other rot types attack wood differently and propagate slightly differently. 

Dry Rot Early Signs

Unfortunately, it’s not easy to identify dry rot in the early stages. For instance, the first two stages are almost invisible.

Nevertheless, you want to keep an eye out for tell-tale signs to catch the problem before it causes costly damage.

Color changes 

The first way of identifying dry rot is by observing the color. Dry rot comes in various colors depending on the rotting stage and location.

  • Whitish growth resembling thick cotton: At the mycelium stage, dry rot forms a whitish growth resembling cotton. Alternatively, it may resemble a snakeskin, sometimes with teardrops. Brittle strands sometimes form over the mycelium but crumble and crack when touched.
  • Pancake or blanket-shaped sporophores: Dry rot sporophores are easily visible. However, many people confuse them with mold. You’re dealing with dry rot, not mold, if the pancake-shaped mass is orangish, with red spore dust around the blanket.
  • Silky-grey to white mushroom color: Finally, dry rot sometimes develops a silky grey or mushroom-white top layer in drier conditions. The “skin” is often blown away by the wind. Otherwise, it sticks around with yellow or lilac patches.

You may observe a few other signs of dry rot. The only problem is that it’s easy to confuse the signs with wet rot and mold. So, we recommend analyzing the additional signs alongside the color of the affected area;

  • Mushroom-like odor: Dry rot produces a characteristic damp, musty, fungal smell that you can feel several feet away. The dry rot smell may not necessarily mean full-blown rotting is underway. But it always points to rot-like conditions.
  • Deep cracks across the wood grain: Dry rot leaves deep cracks across (not along) the wood grain, forming little cubicles. These cracks are often lined with mycelium.
  • Rotting on visibly dry surfaces: The main distinction between dry and wet rot is that wet rot only grows on highly porous and damp surfaces, typically with 50% moisture. Meanwhile, dry rot can grow on visibly dry surfaces, including plasterwork and paintwork.

Treating Dry Rot

The first step to treating dry rot is removing the moisture. This often involves repairing pipe leaks and rain damage. Without moisture to sustain the colony, the fungi die, and the affected wood dries up.

Next, you need to dry the affected wood. Airing the boards in the open sun to dry is one option. Alternatively, use heaters or a hair dryer for smaller wood pieces.

Indeed, heat treatment is now considered a practical stand-alone rot removal solution. Two particularly common heat treatment solutions are heat fumigation and microwave treatment.

Heat treatment utilizes heaters and lamps, while microwave treatment utilizes a microwave. Unfortunately, both methods are expensive.

After eliminating moisture sources, drying the rotted wood with a heat source, and enhancing ventilation, consider the following;

  • Remove rotten wood sections: Badly rotted wood sections may be too weak to support the structure. Moreover, rotten wood structures increase the risk of injuries and fatalities. So, it’s best to remove and replace them with fresh, stronger wood.
  • Replace with pre-treated timber: When replacing rotten wood, consider pre-treated replacement timber. Pressure-treated wood is not 100% rot-resistant . However, it’s much more water-resistant than ordinary lumber. Therefore, it doesn’t rot readily.
  • Treat sound wood surfaces with a dual-purpose dry rot treatment fluid: Finally, after replacing the worst-affected parts, it’s time to treat the structure with a dual-purpose dry rot treatment. The best dry rot treatment solutions are borates and glycol.

Borate-Based Wood Preservatives 

Borate-based preservatives are best for treating new wood, though you can also use them to treat existing, rot-damaged sections.

The treatment process involves spraying a borate solution over the affected surfaces or drilling holes in the affected area and injecting the solution into the holes. Bora-Care and Tim-Bor are the best-known borate rot treatments.

They are water-soluble solutions that easily penetrate the wood surface for deep rot and termite protection. Unfortunately, water-solubility also means borates may destroy the surface’s protective coating.

Glycol Preservatives 

Glycol is a critical ingredient in many types of antifreeze and other de-icing solutions. You have two options – ethyl glycol and propylene glycol.

The former is highly effective against termites and rot-causing fungi. Unfortunately, it’s toxic to humans. Meanwhile, propyl glycol is less toxic but not as powerful against rot as ethyl glycol.

A major advantage of glycol over borate-based preservatives is that wooden boards and structures readily absorb glycol without surface damage.

However, beware that glycol easily washes away when you rinse the surface or in high-moisture environments.

Household Solutions

If you cannot find borates or a glycol-based solution, a few homemade solutions can help eliminate rot. These include hydrogen peroxide, baking soda, and vinegar.

The only downside is that these are mainly temporary solutions that become ineffective in several months to a year. So, you must replace them often.

Dry Rot Treatment Costs

Unfortunately, treatment for dry rot can be expensive. Although you may only spend a few hundred (typically under $300) if you catch the problem early, a dry rot outbreak costs up to $2,500 to treat.

The costs are higher if you need to replace damaged wood sections. For instance, repairing a rot-damaged floor joist costs $4,000 to $12,000, depending on various factors.

Wet Rot Causes, Signs, and Remedies

What is Wet Rot?

Wet rot is the natural decay of lumber due to high moisture levels. It’s almost similar to dry rot. However, wet rot occurs in timber with 50% moisture and rarely in wood sections with less than 30% moisture.

In contrast, dry rot can attack woods with as little as 20% moisture. Another major difference between wet and dry rot is that wet rot is localized to damp wood and doesn’t spread to dry wood parts.

This makes it less invasive than dry rot, which easily spreads to dry parts of the affected wood. But beware that wet rot is just as dangerous as dry rot. It significantly weakens the wooden structure, diminishing its weight-bearing capacity.

Types of Wet Rot

There are many types of wet rot fungi with different characteristics and modes of attack. But the most common types are as follows;

  1. Brown rot: Brown rot fungi feed on the timber’s cellulose while leaving the lignin intact. Therefore, the timber becomes darker and typically shrinks and cracks. Cuboidal (cubical) cracking is especially common.
  2. White rot: White rot fungi feed on the timber’s cellulose and lignin, leaving the timber fibrous internally and on the external surface. The affected section is lighter than the rest of the wood because of lignin loss.
  3. Cellular fungus (Caniophora Puteana): Cellular fungus attacks the wood’s internal structure, causing a thin surface skin. It’s characterized by yellow coloration in the early days, which gradually transforms into a dark brown sheet with fine brown threads.
  4. Mine fungus (Fibroporia Vaillantii): Mine fungus mainly attacks softwoods, causing a whitish growth with light orange patches. You may also notice coarse, white threads emerging from the affected area.
  5. Oyster fungus (Pleurotus Ostreatus): Oyster fungus mainly attacks paneling boards and other manufactured boards. It is often a wool mat with a steel or fawn-colored mushroom-like body. Oyster fungi don’t form strings/strands.

Other types of wet rot are Donkioporia Expansa and Asterostroma spp. However, they are much rarer.

Causes of Wet Rot

The main requirement for wet rot development is high moisture. Any wood surface with moisture levels above 30% is highly likely to attract wet rot fungi.

Moisture sources vary depending on the environment. For instance, broken pipes can cause water damage in the basement, resulting in a wet rot outbreak.

Meanwhile, furniture may get wet rot from a leaky roof and undressed water spills. A leaky washing machine, leaking shower tray, and defective plumbing are other common sources of moisture in the home.

Remember that there are millions of wet rot fungi floating in your home, seeking habitable conditions. These fungi gladly hop onto any damp wood and establish a colony.

Does Wet Rot Spread?

Technically, no. Wet rot, unlike dry rot, doesn’t spread. However, this doesn’t mean wet rot fungi don’t expand their colonies. They do. However, wet rot spreads within the confines of the damp environment – not onto dry surfaces.

Signs of Wet Rot

Identifying wet rot is even more difficult than dry rot because it often occurs in dark, poorly ventilated, non-visible areas.

For instance, wet rot is most common in cellars, roofs, lofts, and under floorboards. You may also find it in door frames, window frames, and under stairs.

So, you should inspect and clean these areas regularly to catch wet rot early. Telltale signs include;

  • Darkened timber or dark brown staining on the affected area.
  • Splitting or longitudinal cracks along the wood grain.
  • A damp, musty smell or smell of rotting wood.
  • Soft, spongy spots or general dampness.
  • The affected section caves in easily when you prod it with a screwdriver.
  • Localized fungal growth.
  • Cracked appearance especially as the damp timber dries.
  • The surrounding wood surfaces are bleached (lighter) than the affected area.
  • Localized fungal growth (wet rot doesn’t spread much).
  • Mycelium strands in the affected area.
  • Discoloration and loss of strength.

Wet Rot Treatment

The best way to address wet rot is through professional treatment. Why? Because finding it is very difficult, and you never really know whether the problem is gone for good.

For instance, you may leave a few wet rot fungus spores behind, triggering another wet rot outbreak. Nevertheless, the treatment process is the same whether you call a professional or do it yourself;

  1. Identify and eliminate the moisture source: This often includes rectifying plumbing issues, fixing water damage in the basement, addressing high indoor humidity, and fixing leaking roofs. You cannot completely eliminate wet rot without addressing the moisture cause.
  2. Allow the timber to dry: You can wait a few days for the affected sections to dry. Alternatively, consider heat treatment to accelerate the drying process. Microwave treatment is another option.
  3. Apply fungicides and wet rot wood hardeners: Wet rot hardeners are chemical formulas that bind and harden decaying wood to provide a solid base for filling. Most formulas set rock hard, restoring wood strength and function. The Ronseal Wet Rot Wood Hardener is the best-known wet rot hardener.
  4. Replace all badly weakened wood pieces: Removing and replacing weak rotted timber restores the structure’s strength and function while preventing wet rot spread. Consider pressure-treated replacement lumber.

Wet Rot Treatment Cost

Professional wet rot repair costs vary from $150 to $25,000, depending on the extent of the damage. For instance, many professionals charge a minimal retainer (typically $150) to fix wet rot on a door frame.

Meanwhile, replacing a rotten siding costs up to $1,500.  DIY rot treatment is much cheaper, especially if using home remedies, such as vinegar and hydrogen peroxide. However, professionals guarantee a longer-lasting solution.

How to Stop Wood from Rotting

Unfortunately, dry and wet rot can be very costly. So, prevention is better than cure. Consider the following prevention tips;

  • Always use pressure-treated or decay-resistant wood.
  • Stain or paint all sides of exterior wood.
  • Don’t lean anything agains your building.
  • Address potential moisture sources promptly.
  • Conduct annual inspections to catch rot early.
  • Fix wet and dry rot signs early.

FAQs

What does dry rot look like? 

Dry rot looks like a gray white skin mixed with yellow and lilac patches. It can often be mistaken for ordinary mold or mildew. However, dry rot is distinguished by its characteristic cracking pattern. If you see this cracking pattern on wood, it’s likely that the wood has been infected by dry rot fungus.

What is dry rot on wood?

Dry rot is a type of fungus that affect wood. The infection usually starts at the surface of the wood and spreads inward. The wood becomes soft, brittle, and cracked. The fungus can also produce a mycotoxin that is poisonous to humans.

What is white rot on wood?

White wood rot forms when fungus digests the cell walls of the wood which makes it rigid.  The fungus eats away the cell walls (lignin) making the wood weak and susceptible to decay. Over time, the affected areas turn white as the fungus grows and spreads.

What does rotting wood look like?

A rotting wood looks like a whitish cotton texture on the surface. sometimes it’s grey white which is a sign of a fungal attack. The result is a spongy, lightweight material that can be easily crushed in your hand. If you see closely, spores develop around the rotting surface in yellow or purple colour.

What does rotting wood smell like? 

Rotting wood smells musty and earthy. This is because the compounds that give rotting wood its distinctive smell are similar to those found in mold and dirt. When you combine these smells with the dank, humid environment in which rot thrives, it’s easy to see why rotting wood would have such an unpleasant odor.

Wet rot vs dry rot

The difference between wet and dry rot is that wet rot requires high levels of moisture to thrive, while dry rot can exist in lower levels of moisture. This is why wet rot is more common in buildings exposed to water damage.  Yet, dry rot is more common in buildings that are poorly ventilated.

What is dry rot in a house?

Dry rot is in a house because of poor ventilation. When air inside a house isn’t circulated well, it creates a perfect environment for dry rot to form. It means there’s not enough moisture in the air to keep wood healthy and strong, and the fungus that causes dry rot will start to grow.

What is the best dry rot spray treatment?

Borate is the best dry rot killer because, as a salt, it’s highly water soluble and easily migrates through wood. Once in the wood, borate becomes an active ingredient and starts to destroy the fungus that causes dry rot. It’s also non-toxic making it a safe choice for use at home.

Is dry rot dangerous?

Yes, dry rot is dangerous. In fact, it is the most dangerous of all other timber fungi. It can quickly damage furniture, flooring and other wooden objects. Besides structural damage, dry rot can also cause respiratory complications and even death.

How fast does dry rot spread

Dry rot spread depending on the severity of the rot and environmental condition. However, in optimal conditions, dry rot can spread up to 80 mm per day.  It does not need a lot of moisture to grow, so that means a temperature range not exceeding 19 °C to 21 °C.

What causes dry rot in homes

Dry rot in homes is often caused by insufficient ventilation. When there’s not enough air moving through the home, moisture can build up and create an ideal environment for fungi to grow. You’ll mostly realise dry rot behind wallpaper or paint these houses where moisture is blocked from reaching them.

Summary

Wood rot is a big problem for woodworkers and the construction industry. It weakens wood, discolors surfaces, and can easily bring down a building.

Moreover, rot poses various health and safety concerns. Fortunately, you now know how to tell if wood is rotten, plus wood rot remedies and prevention tips.