What are Wet Rot and Dry Rot?

Outdoor decks are important recreational spaces in family life. When you are enjoying leisure time on your deck, you may notice some unsightly things. For example, the boards on the deck may have quietly turned black. The wood may show signs of rot and peeling. This condition may be wet rot or dry rot.

Sometimes, these signs of rot are inconspicuous, but they should not be ignored. Deck rot can cause many problems. However, don’t worry. This article will explain the differences between wet rot and dry rot. Understanding these differences will help you better prevent and address them.

Characteristics of Wet Rot and Treatment Measures

Wet rot is a common form of decay. It is caused by a variety of fungi, which primarily grow on wood with a moisture content exceeding 50%. Below is a detailed explanation of wet rot and its treatment methods.

What is Wet Rot?

Wet rot is the natural decay of wood in high-humidity environments. These decay fungi thrive in moisture-rich conditions. Wet rot has a broad scope of damage. Moist wood, plaster, wallpaper, and carpets may all be affected. Additionally, fungi can break down the cell walls of wood, absorbing the nutrients needed for their growth. Over time, the wood gradually loses its original properties.

Types of Wet Rot

Wet rot is a general term for various fungi. Wet rot is primarily divided into two main categories:

• White Rot: When wood is attacked by wet rot fungi, the surface develops a whitish appearance. White rot fungi simultaneously break down both lignin and cellulose in the wood. Additionally, the wood’s texture changes. The wood becomes soft and spongy, and can even be easily crushed.
• Brown Rot: Brown rot is darker in color than white rot. Sometimes, wet rot fungi cannot digest certain lignin in wood, so they feed on sugars and cellulose. This causes the infected wood to turn brown.

Causes of Wet Rot

Wood rot is more likely to occur when wood is exposed to a damp environment for an extended period. A damp environment creates favorable conditions for fungal growth. In such cases, wood rot is more likely to occur, causing the wood to soften. The primary causes of wood rot in decks include the following:

• Structural Defects in the Deck: Defects such as damaged deck planks or leaks allow moisture to penetrate.
• Poor Drainage: A malfunctioning drainage system in the deck leads to prolonged water accumulation, which seeps into the deck structure.
• Ground Moisture: Moisture rising from the soil infiltrates the wood.
• Condensation: When temperature differences are too large, condensation forms on the wood surface. Prolonged moisture leads to decay.
• Poor Ventilation: Insufficient airflow within or beneath the deck prevents moisture from dissipating, keeping the wood in a high-humidity environment.

Hazards of Wet Rot

Wet rot poses multiple hazards to deck structures. It gradually reduces wood strength, and in severe cases, may even pose a collapse risk. Therefore, wet rot must be addressed immediately upon detection. In severe cases, the entire piece of wood may need to be replaced, significantly increasing repair costs.

How to Prevent and Address Wet Rot

To prevent wet rot, proper waterproofing and ventilation improvements are necessary to prevent wood from becoming a breeding ground for fungi. Generally, reducing wood moisture content below 15% and maintaining environmental humidity below 50% can prevent wet rot.

If the deck has minor rot, promptly remove mold and mold stains using appropriate cleaning agents. If the boards are severely rotted, you may need to replace the entire section of wood. Alternatively, you can replace it with composite decking made from wood fibers and recyclable plastic. It has excellent mold-resistant properties and is easy to clean and maintain.

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Characteristics and Prevention/Treatment Measures for Dry Rot

Dry rot fungi typically germinate on wood with a moisture content of 20%–30%. Below is a detailed description and treatment method.

What is Dry Rot?

Dry rot is a severe fungal decay that feeds exclusively on wood cellulose. It poses a fatal threat to the wooden structures of buildings. Unlike wet rot, the surface of dry rot often remains dry to the touch. It causes crisscrossing cracks inside buildings, eventually shattering into block-like pieces.

Causes of Dry Rot

Dry rot occurs when dry rot spores are activated and spread under specific environmental conditions. Dry rot spores floating in the air require contact with moist wood with a moisture content of around 20% and access to oxygen to break out of their dormant state and begin growing.

The causes of dry rot are similar to those of wet rot. Factors such as standing water and humidity can trigger dry rot. Once the mycelium forms, the fungus can maintain humidity through its own metabolism. At this point, it no longer relies on an external water source.

The Hazards of Dry Rot

Dry rot can cause devastating damage to building structures. The fungus breaks down wood cellulose, causing the wood to crumble into pieces. Its mycelium has stronger spreading and diffusion capabilities, making it easier to cause cross-regional infections. The repair costs for dry rot are also very high.

Additionally, if dry rot occurs in your building structure, the area will emit a damp, earthy odor. Fungal spores can cause coughing and asthma, posing health risks. Decaying wood also attracts pests, which further accelerates wood degradation. Ultimately, these factors severely impact living conditions.

How to Prevent and Address Dry Rot

The prevention methods for dry rot are similar to those for wet rot. The key is to keep the wood dry and ensure proper air circulation. You can also apply primer and paint to the surface of the wood. Alternatively, you can use composite decking with a protective layer. COOWIN‘s capped composite decking effectively resists dry rot fungi.

Once dry rot is detected, isolate the affected area to prevent spore spread. Reduce environmental humidity. Remove floors, walls, and other concealed areas. Determine the extent of fungal spread. Then thoroughly remove and disinfect the affected area. Replace the wood with pressure-treated lumber or composite decking materials. Treat any remaining healthy wood with a preservative.

What are The Main Differences between Wet Rot and Dry Rot?

Both wet rot and dry rot are caused by fungi. However, they have many differences, including:

Dependence on Moisture

Wet rot requires a high-humidity environment with wood moisture content exceeding 50%. Additionally, wet rot depends on external water sources. If the external environment becomes dry, wet rot will cease.

Dry rot can grow at wood moisture content levels of 20%-30%. It can generate moisture by decomposing the wood itself. Therefore, once it occurs, it can spread to dry areas.

Fungal Types and Destructive Capacity

Wet rot is caused by various fungi. It has diverse types. It primarily softens wood, with relatively weak destructive capacity.

Dry rot is primarily caused by a single fungus. It decomposes wood cellulose, causing wood to crack into block-like pieces. Dry rot has a stronger destructive capacity and can easily endanger building structures.

Main Characteristics and Spread Methods

Wet rot causes the wood to become moist and soft, appearing white or brown. Its surface may have a mold layer or mold spots. Additionally, the decayed areas are confined to moist environments and do not actively spread.

Dry rot causes the wood to become dry and shriveled, appearing dark brown with regular cracks. Dry rot also forms mycelium and fungal threads. It has strong spreading capabilities and actively spreads to surrounding areas.

Treatment Difficulty

Wet rot is relatively easy to treat. Simply clean the moldy areas and keep them dry. Most homeowners can opt for DIY solutions.

Dry rot, however, often hides in concealed areas of buildings. In many cases, homeowners need to seek professional teams for thorough removal and deep disinfection. Otherwise, it may lead to missed areas and recurrence.

Conclusion

Both wet rot and dry rot can impair a building’s performance and lifespan. By understanding the causes and preventive measures for wet rot and dry rot, you can avoid their impact on your home and living spaces.

Additionally, composite decking materials with excellent mold-resistant properties can protect you from the issues caused by wet rot and dry rot. If you’d like to learn more, COOWIN can provide you with samples of various composite decking materials.

FAQ

How to Determine if Decking has Wet Rot or Dry Rot?

Observe if there are areas of blackening or browning in the wood color. Touch the boards to see if they are easily dented. If these characteristics are present, it may be wet rot. If irregular cracks appear on the surface, it may also be dry rot.

Additionally, check if there is a smell resembling decaying leaves or soil. Observe if there are visible mold or mold spots on the surface. In the case of dry rot, fine, fluffy white fungal threads or black root-like fungal strands may also appear on the wood surface or in the cracks.

Can I Handle Dry Rot Myself?

If you know how to remove and replace the damaged wood, you can handle dry rot yourself. However, if you are unsure how to proceed, it is recommended to contact a contractor or renovation company. They typically handle the removal, replacement, and treatment of the wood simultaneously.