Why Does Pressure Treated Lumber Have Small Holes or Incisions?

pressure treated wood with incisions

The small holes in pressure-treated lumber, known as incisions, are quite a mystery. And mysteries are meant to be solved. So, I put on my detective hat, and after doing some research on the topic, this is what I found. . .

Some lumber, like Douglas fir, will not readily accept the chemicals used in the pressure-treating process. However, if the wood is covered with small incisions, then the chemicals are readily absorbed. 

Not all pressure treated wood will have incisions. Why? Because some wood, usually eastern pines, are much better at absorbing the needed additives during pressure treatment. 

Most people don’t find these small holes very appealing. Some even wonder if all these little incisions cause the board to lose structural integrity. 

In the sections below, we will answer all these questions and give you practical advice on combatting any issues. 

Understanding Incisions in Pressure Treated Lumber 

In this section, we want to give you a little more information about the incisions in treated lumber. Some people are very familiar with seeing these little dents in the side of their wood. However, others are not. 

Regardless, everyone should understand what incisions are for and what it means for your project

Here are a few things to know:

  1. Incisions in lumber help with the pressure treatment process
  2. Incisions have a small impact on structural integrity 
  3. The incisions are not used in every area 

Alright, let’s unpack these. 

Incisions Help with Pressure Treatment 

Some types of woods take the pressure treatment process very well. However, others need these incisions to help them along. To properly understand why the incisions are necessary, we must first briefly describe the pressure treatment process. 

When wood is pressure treated, two things happen: 

First, the lumber is placed in a depressurized chamber. Then the chamber is closed and filled with the preservative component. 

Second, the pressure is reintroduced to the closed chamber, forcing the preservative into the lumber. 

This second step is where the incisions come into play. According to regulations, the preservative needs to penetrate to a specific depth for the wood to be correctly pressure treated. 

Defiant, some woods resist the preservative. 

These resistant woods, like the Douglas fir, are run through a machine that dots the wood with a bunch of incisions. These incisions in the wood allow the preservative to seep deeper into the fibers of the lumber. 

Think of the process like a sponge in a sealed plastic bag. If you poke some holes in the plastic bag, the sponge will be able to absorb water. Similarly, when they poke small holes in the lumber, it allows the wood to absorb the preservative, leading to a more rot and weather resistant board.

Now, let’s figure out if these little holes affect the structural integrity of the pressure-treated lumber. 

Incisions Affect on Structural Integrity 

These little dots have a semblance to bullet holes in the side of a car. And you might think, this can’t be good for the wood.

However, others might not think anything of the incisions. Regardless of which boat you sail in, you may be surprised to find out that the incisions do affect the structural integrity of pressure-treated lumber.

There have been several studies that look into the structural integrity of pressure-treated wood that undergoes the incision process. Both the studies we reviewed appear to show a relationship between the board’s structure and the incisions. 

In this study on the effect of incisions and pressure treatment on two-inch lumber, the conclusion is that the incisions will negatively impact the board’s shear strength – or strength against twisting forces.

This makes sense, as the incisions will damage the external fibers of the wood. Of course, this isn’t a massive decline in strength; however, it may be something to consider before beginning a project

Should you still use lumber with incisions for structural projects? Yes. The decrease in strength isn’t going to be moon shattering. 

In light of all this, you might want a treated board that doesn’t have these incisions. In the next section, we will discuss different parts of the US that do not have pressure-treated wood with incisions. 

Can I Get Pressure Treated Wood Without Incisions 

You can undoubtedly find treated wood that doesn’t have incisions. However, this is more likely in certain areas and in certain woods. 

Southern Yellow Pine is a common wood in the eastern United States. It also happens that this wood is more conducive to pressure treatment. As a result, there is no need for the incisions you see in other wood. 

In contrast, the previously mentioned Douglas Fir is a tree that grows readily in the pacific northwest states of Oregon and Washington. The Douglas fir does not soak up the chemical preservation as readily as the southern yellow pine – thus, the incisions are made in the wood. 

What is the result? Well, if you reside in the western United States, you are much more likely to encounter wood with incisions. In the same respect, those in the east will have access to non-incised wood. 

But wait, you say, I live in the west, and I don’t want all those little incisions in my lumber, is there anything I can do? Yes, and we will cover these hints and methods in the next section. 

How to Get Rid of Incisions in Pressure Treated Lumber  

So, you’re trying to build the finest deck in town, but you realize the pressure-treated lumber you ordered is checkered with small incisions. Is there anything you can do to improve the appearance of your deck? 

While there is no magical way to eradicate the incisions, there are a few things you can do. 

Here are three ideas: 

  1. Wait 
  2. Sand and paint 
  3. Use an alternative material 

Those are the ideas, now let’s look closer. 

Wait for Incisions to Soften 

With time, most people report that the little incisions in their pressure-treated wood will lessen. As the weather and temperature shift and change, the treated wood will also change. The result will be less pronounced edges. 

However, this isn’t likely to altogether remove the incisions from your lumber. In fact, depending on the depth of the incisions, and how many there are, waiting could do very little. 

Before you purchase wood, it’s helpful to shop around different lumberyards. Some areas might have more or less pronounced incisions. Other places might have pressure treated lumber void of all incisions. 

If you have no alternative or your deck is already built, we give you a few tips in the next section. 

Sand and Paint to Hide Incisions 

We’ve included this idea to highlight many of its flaws. Sanding and painting over your treated wood can be done, but it’s not as straightforward as you might think. There are several reasons why professionals recommend you hold off painting your pressure-treated boards. 

Here’s why. 

First, pressure-treated wood is usually full of moisture after the treatment process. As a result, it won’t take paint very well. Often, you will see pealing and cracking of the paint within the first year or so. 

Pealing paint looks worse than no paint at all. 

Second, extensive sanding of pressure-treated lumber isn’t the brightest idea either. Pressure-treated lumber used to contain arsenic. In recent years, pressure-treated lumber contains safer additives. However, you still don’t want to be breathing in this sawdust. 

In conclusion, if you feel you must sand and paint your treated wood, do the following things:

  1. Wait until the wood is dry. The wood will usually dry after about 60 days. 
  2. Apply primer and sealer before you apply the paint. You want to give your paint the best chance at maintaining its integrity. 
  3. Be sure to wear a sophisticated dust mask if you do any sanding. As we discussed, you don’t want to breathe in the pressure-treated wood particles. 

Alright, let’s talk about our final, most viable solution. 

Use an Alternative to Pressure Treated Lumber 

We all want the durability and longevity of pressure-treated lumber; however, we’d rather not deal with the adverse effects of incisions and dangerous chemicals running off into our yards. 

Thankfully, some alternatives provide strength and beauty.

This article outlines seven alternatives to pressure-treated wood. 

You’ll find that there are a myriad of alternatives.

Here are just a few: 


Aluminum is light and rust-resistant. It is a common alternative to treated lumber. 


Weather-resistant and easily paintable, vinyl is another alternative to pressure-treated lumber. 


Trex is a wood and polymer mix that strives to provide the best of both worlds. 


Pressure-treated lumber sometimes needs incisions to help the lumber accept the preservative. However, not all pressure treated lumber has these marks. 

You are more likely to see pressure treated lumber without incisions in the US’s eastern regions, where the wood more readily accepts the chemical treatment. 

If you’re looking for ways to get rid of the incisions, there are a few things you can do. Either paint over the marks, being mindful that paint doesn’t hold very well on pressure-treated wood, or use a durable alternative, like aluminum, vinyl, or Trex. 

5 thoughts on “Why Does Pressure Treated Lumber Have Small Holes or Incisions?”

  1. Thank you for the article. What I was looking for is if you could use wood filler on the incisions, I decided to try a small area of my posts with stainable filler.
    You’ve misspelled peel in the paint section, thought you would want to know.

  2. Fascinating discussion. Saw these marks on board used in bridges in Rocky Mountain National Park, and was curious as to their origin. Thanks very much for the information.

  3. About eight years after installing 6×6 “treated” lumber I got to thinking was this full penetration treated or “deck grade” penetration so I read up a bit. From my time in Alaska and the West Coast I was familar with the penetrations in AWW timber.
    My cottage is in coastal Eastern Canada (PEI). Your analysis helped me to understand that what I used was Eastern Spruce and it did not need the little penetrations. This helps me to sleep better.

    I am thinking about digging down 2′ and adding a layer of polyethylene wrap to avoid the more deteriorating aspects of these northern winters. I even thought I would rub on some axle grease to avoid frost heaving. The posts are 60″ deep and anchored to 24″ diameter concrete footings using galvanized post bases as required by local codes for “cold” footings. The construction is now about 8 years old. On inspection I did not see any deterioration after digging down about 20″. Would you recommend adding the poly as a precaution against ground plane rot?

  4. I was reading this article to select type of wood for a small deck. Comparing PT lumber with other lumber in the West is
    always challenging. Specially now, various claims are made of staining PT wood but not all facts about the incisions are disclosed.
    In this article, you have explained how the incisions are different are a feature of pressure treated D.fir and it opened my eyes.
    It is too bad in selling PT lumber, no information is provided as the type of wood and it adds to confusion. No stamp or markings in the lumber.
    Thank you much.


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