How the Sun’s UV Rays Cause Wood Degradation Through Wood Rot

Right off the bat, it seems like a tough combination — wood, water, and sun. Yet, when we have a dock or pier, we are throwing these three variables into the mix, all together, and in many cases, just hoping for the best. Thus, it really shouldn’t be a surprise that when mixed together, this can be a battle that wood has a tough time winning.

For our dock’s piers and posts to stand any kind of chance of holding up under the sun’s UV rays plus water (from the body of water itself, humidity, and rain) and then living organisms that either naturally feast on wood or that are attracted by damaged wood, we have to understand this multivariate process and prepare for it.

Wood’s Natural Vulnerabilities that Make It Subject to Wood Degradation

The very nature of wood makes it vulnerable to the aforementioned types of harm or damage. Yet, in many cases, wood is still the best — or even the only — option for our dock piers and posts. Thus, we must learn to manage and mitigate that risk as much as possible.

While we might think water is the biggest of these threats, that’s not really true when considered on its own. However, when UV damage wreaks havoc on wood, the damage —and potential damage —of all kinds of water and moisture intensifies.  The rays of the sun — UV light — destroys the lignin of wood. This is the part of wood that makes the cell walls of wood hard and strong.

Over time, as the sun continues to beat on the wood, the wood becomes less resilient and then eventually will crack and/or slough off its protective surface. This means that the wood will take on more water inside where that moisture starts to do additional harm—causing deterioration of fiber and even attracting mold and fungi. All of this also creates a prime condition for both wet rot and dry rot—either of which can warp and eat away at the wood, causing major cracks, and eventually, total collapse. If you’ve ever seen a dock or pier just “instantly” collapse into the water, you’ve seen the results of this dangerous process at work.

The Difference Between Wet Rot and Dry Rot and Why It Matters

Obviously, with a good portion of your dock’s piers and posts in the water all the time, you will likely experience some degree of rot. However, keeping the pier posts clean and damage free can help to prevent it from becoming a huge problem.

But how do you know if you have wet or dry rot and why does it matter?

Again, the first key in addressing dry rot is prevention. Aside from that, it’s knowing the signs and differences of each type so that if you do see (or smell!) the signs, you can act quickly.

Dry Rot

If you encounter dry rot, it is more likely to be on the surface of your dock or on the corners, edges and underneath the deck of your dock. The edges are especially vulnerable because the sun and the water together create a cycle of wet-and-dry that makes this area prime for the specific fungus that causes dry rot. Dry rot is only caused by the fungi Serpula Lacrymans but it can affect ANY unprotected wood that has a moisture content of above 20%.

Once it’s started, dry rot can spread to other areas rapidly until one day, you might notice the top of the dock cracking. Next, you might even have a simple step punch a hole through the dock’s edge or surface. If dry rot gets that bad, you need to  check quickly and see if it’s spread to the piers and posts. If not, and it appears isolated, you can try repairing the damaged lumber. If so, then you need to check with an experienced dock professional immediately.

Wet Rot

Wet rot doesn’t necessarily spread like dry rot but it can do a lot of damage too.

Wet rot occurs — like it sounds — on wood that stays mostly wet. Usually, this wood is untreated and damage — at some point somewhere — allows moisture to not only impact the wood’s surface, but its insides too.

Thinking back to the above discussion about how the sun destroys the wood’s lignin, you can likely imagine that this creates that vulnerability where water can seep into the wood’s internal structure and start doing significant damage. And as with high blood pressure in a person, this type of damage can be a “silent killer” to wood because you might not notice it until it’s fairly far gone.

However, you should investigate if you see these signs of wet rot:

  • Wood that has become soft and spongy
  • Discolored wood
  • Mycelium strands present on wood
  • Paint finish appearing damaged or cracked
  • A damp, musty smell

Preventing Wet Rot and Dry Rot

As we said, preventing wet rot and dry rot forms of wood degradation is much easier than treating wood rot.

Common methods of preventing wood rot, specifically on dock piers and posts, include:

  • Using opaque paints and sealants
  • Adding wood coatings, injections, and other protectants
  • Coating wood with drying oils and compounds
  • Integrating physical barriers
Using paints and sealants to prevent wood rot

Opaque paints and stains that act as wood sealants —with more color and pigment — can do a good job of blocking the UV rays that often start the wood degradation process. Some UV may get through but to a much lesser degree than if the wood was painted or sealed with a product that is more transparent.

Adding wood coatings, injections, and other protectants to protect against wood rot

Paints and stains aren’t the only things that can be added to wood to protect against wood rot. Humidity is another big factor that when combined with sun, makes wood prime for rot. Many wood coatings and injections help to absorb some of the incoming UV radiation and dissipate heat, lessening the damage from both the sun itself AND humidity. You can also inject wood with formaldehyde resin (PF) and this helps protect the internal structure from these outside stressors as well.

Coating wood with drying oils and compounds

When certain oils are applied to wood and then react with the oxygen in the air, they create a film that is almost solid. This film then protects the wood from moisture AND UV impact.

Integrating physical barriers to prevent moisture damage to wood and ultimately, prevent wood rot (or even treat mild wood rot too)

Before damage to pier posts and piles or the dock wood has occurred, applying a physical barrier to dock piers and posts like pile wrap, can be a great wood damage — and wood rot preventative — treatment. Such pile wrap products like our Pier Protector are often made of UV-resistant (or as in our case UV-blocking) materials and create a physical barrier between the wood and water, and wood and living elements, too.

Even better, if you are only facing mild wood damage to the surface of dock piers and posts, you might still be able to benefit from pile wrap. The key is whether or not the damage IS only at the surface and if you can get the posts relatively clean before wrapping them. If so, this might be just the answer you are looking for in terms of total and complete pier post protection.

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