I think every child in the Western Hemisphere has had the opportunity to see an unused 2×4 board. It’s a beautiful thing: the prospect of what it will become once a builder has gotten his hands on it. I specifically mention children, because when I was a child, I couldn’t resist its allure as my grandpa and dad were busy building and cutting down the boards. My curiosity was always fulfilled when I would take a hammer to it to see how easily it would dent and make the perfectly round shape of the hammerhead. It was almost satisfying. I got away with a lot, so I was usually never reprimanded for this action, but it’s also likely because it was being used to frame out a wall.
My point is that 2×4 boards are typically made of untreated pine, a softwood that easily dents. I mean, I would actually write on the board with my fingernail! As a framing piece, this isn’t a big deal because it is covered by drywall, but what about the pine that is used for building furniture or projects that are easily seen, like flooring and shelves? There are a few techniques used to harden pine wood that can be done once you get it home.
It’s important to be aware of this because pine is a very popular option when building. It is one of the more affordable woods, commonly found, and easy to work with. Most people will tell you to stay away from such softwood when building furniture, but sometimes pine works best. The best ways to harden pine is to use a chemical base, a tough topcoat, or use fire. Yep, fire.
How Soft Is Pine?
Pinewood is one of the softest woods available for construction. The lumber industry uses the Janka scale to label how hard a wood is, meaning its resistance to dings and ease of use. The pine genus consists of many types of pine, and because of this, there are quite varying degrees on the Janka scale. It’s important to know which type of pine you are using and to pick a stronger pine for projects that will be seen.
For reference, ebony, an extremely hard wood, falls at 3220 on the Janka scale. The highest species of pine on the Janka scale is red pine, which has a number of 1630. However, most lumber yards use white pine for construction-grade lumber. This has a hardness level of 420, while Eastern white pine is at the bottom with a Janka number of 380.
So, when choosing which pine wood you want, consider looking into the Janka scale or simply ask the lumber store workers which will be best for you.
What about Heart Pine?
While there are several types of pine trees used for lumber, you may have heard of heart pine, which is heralded as a hardwood. This is not a species of pine; this is actually a specific part of the tree.
You see, as a tree grows and gets thicker in diameter, the interior of the wood dies. This causes the wood to harden quite a bit because it no longer contains sap and its tunnels to keep that area of the tree full of nutrients. Because of this, it is often a popular choice for building when someone wants harder wood. In fact, heart pine falls at 1225 on the Janka scale.
Of course, because the lumber industry attempts to have such quick turnover with the trees it uses, heart pine is rare in the industry. You’ll often find reclaimed heart pine called antique pine since it was cut down back when trees were not milled in mass numbers.
Just keep in mind that it can take anywhere from 200 to 500 years for a tree to contain nearly 100% heartwood. So, that means that Shakespeare could have planted the tree you want to be cut down for your floor. Okay, probably not, but he likely breathed the oxygen provided by that tree!
How About Chemically Treated Pine?
Chemically treated, or pressure treated, pine is very common in exterior builds. It is pretty accessible at home renovation stores and costs about the same as untreated pine. To treat the pine, the milled wood is soaked in a chemical to make it weather- and bug-resistant. It is then added to a tank that is depressurized to press the chemicals deep into the grain of the wood.
Because many of these chemicals are hazardous, the process must be completed before sale. Lumber yards provide the pressure-treated boards either fresh (still wet) or dried (air- or kiln-dried wood).
While it seems that this is the same as the wood hardener chemicals, it is not. The chemicals used will prevent the wood from rot, fungus growth, bug infestation, and uneven staining.
However, they are not chemical hardeners, and they do not change the integrity of the boards. Do not be fooled by anyone who would tell you that the pressure-treating process actually hardens the wood. It does not.
How Do I Harden Pine?
While there is no way to make pine as hearty as some of the hardwoods found on the Janka scale, there are chemicals and varnishes that can be used to create a stronger piece. There are four main ways that you can harden the pieces, at least superficially: chemical hardener, epoxy, polycryl, and fire.
Chemical Hardeners for Pine
One of the most popular methods for hardening pine is to use one of the water-resistant chemicals available on the market. Provided that your wood has not already rotted, this technique can be done quite easily and will penetrate the grain of the wood, getting deeper than a varnish would. This usually comes in a can or bottle. You can simply brush the wood hardener onto the wood and allow it to dry. Of course, you should make sure that the wood is clean and dry before applying the wood hardener. You’ll want at least two coats of the hardener, so let the wood dry for about two hours before adding the next layer.
Another option is tung or linseed oil to finish the wood. These oils harden the grain and darken the wood, which prevents the need for an additional stain. Oil also is water-resistant, so it will help prevent moisture from getting into the wood and weakening it. Finally, using a polyurethane finish will complete the project (like flooring) and help to prevent any marring of the wood.
Harden Pine with Epoxy
Epoxy is a bit of a miracle tool to me. It typically comes separated so that it must be combined with something else to make it work. It becomes an entirely new chemical in the process. Typically, modern epoxies need to be added to only water, but there are many kinds still out there. After you’ve made a beautiful honey-like texture, spread it onto the wood, keeping the film of epoxy very even all the way across the board.
Allow the epoxy to dry at least three hours before adding the second coat. Three coats will make the wood strong enough for outdoor use. After you have covered the boards with the second layer of epoxy, you must allow it to cure for about three days. Remember the method of three with epoxy.
Polycryl for Hardening Pine
This is a bit of a cheat because this is also a chemical, similar to the hardeners you’ll use. However, polycryl’s only purpose is to harden wood from the surface. Also called polycrylic, this works very similar to polyurethane on your wood. You’ll use it as a topcoat finish. It is available in several finishes, from matte to gloss. This is available in both spray and paint cans. Since it dries very quickly, polycrylic can be difficult to work with.
Aerosol cans, along with being bad for the environment, do not always provide an even spray and cannot be easily directed. Using a roller for polycryl is more preferable for large areas. You can control the amount of polycryl that goes onto the wood, providing an even coat. This method is not ideal for small, intricate projects since the polycryl will dry too quickly for even coats.
Additional benefits of using polycryl are that it is water-based so it can be easily cleaned up with some soap and water. Since it dries quickly, you do not need to wait as long as you would with epoxy or wood hardener chemicals. It should be dry to the touch in about 30 minutes – though wait at least an hour before adding another coat – and should cure in just 24 hours.
Does Fire Harden Pine?
Yes, as I mentioned, fire is one way to harden pine. The ancient Japanese tradition called shou sugi ban has taken America by storm over the past decade. Many people, especially in the tiny home communities, find that it works great for the exterior of their homes because it makes the wood weather-resistant, bug-resistant, and it doesn’t add weight to the finished product.
To do this, wood is charred slightly. Today, this is typically done using a blow torch. By charring the wood, you shrink the cells of the wood so that moisture and other elements cannot access it as easily. The builder then uses a wire brush to remove any blistered or charred wood that may be loose. A nice wood protectant, like a wood conditioner or polyurethane, should then be added to prolong the life and prevent further chipping. The added benefit of using the shou sugi ban method is that it makes the wood fireproof as well.