When it comes to soundproofing materials, cork is certainly an option to consider if you want to get the most bang for your buck. In fact, cork has many wonderful properties that make it an excellent addition to any soundproofing project. With that in mind, I hope to make this article a complete guide to cork, its acoustic properties, and the many ways we can use it.
Now, I’ve already written about the pros and cons of using cork floor underlayment. For one, it’s a natural material, so it’s pretty eco-friendly. Furthermore, the material is also antimicrobial, which makes it better than many other floor insulation material on the market. However, we’re not going to limit ourselves to talking about using cork for floor soundproofing projects today.
Instead, we’ll discover how you could use cork for soundproofing other areas, such as ceilings or walls. However, before we stray too far from the original topic, let’s begin by answering the most important question.
What Exactly Is Cork?
When most people think of the word “cork,” the thing that usually comes to mind is the plug that’s inserted into the mouth of a wine bottle. However, in this case, I am simply referring to the material that the plug is made of — cork.
As I have already mentioned, cork is a natural material made from the cork oak tree. Most of these trees grow in southwestern Europe, primarily around the Iberian Peninsula, and the northwestern African countries of Morocco, Algeria, and Tunisia. Really, if you stop and take note of how many things in your home are made of cork, you might think that those trees’ numbers would be dwindling by now.
Fortunately, we won’t run out of cork pin boards and coasters any time soon. After all, cork production is actually one of the most sustainable industries on the planet. In fact, the cork oak trees don’t need to be destroyed in order to get the final product. Instead, the harvesters obtain the cork by stripping the tree of its bark — which it can continue to thrive without.
Now that we know what cork is and how it’s made, the next step is figuring out the acoustic properties of this material. However, before we answer the big question, there’s another thing we should know.
How Do We Measure Acoustic Capabilities of Different Materials?
So what makes a material good for soundproofing? Well, certain features can place a product into one of the two main categories of soundproofing materials. Namely, when you go looking for soundproofing materials, chances are that you’re after one of two things:
- Sound absorption, which is what we get from acoustic foam products, or
- Sound blocking, which we get from denser products such as Mass-Loaded Vinyl
In my article on the acoustic properties of wood, I pointed out that wood on its own isn’t really a perfect fit for either category. As I’ve said, sound blocking requires a great density and weight, which isn’t something any block of wood could manage. When confronted with soundproofing products that employ these principles, sound tends to bounce away. So they effectively stop it in its tracks.
On the other hand, many wood-based products are perfectly suitable for sound absorption purposes. After all, wood is a naturally porous material, so it is capable of holding plenty of air. Those air bubbles effectively slow down and trap the sound as it travels. If nothing else, one thing is certain: cork certainly has plenty of air bubbles in it to trap sound.
So to make a long story short, blocking sound requires something that’ll stop it in its tracks. So you need a solid material that doesn’t let air through. Conversely, sound absorption generally requires soft and porous materials that would allow the energy from the sound to bounce inside the material until it dissipates.
Noise Reduction and Sound Transmission Ratings
While I’m on the subject of the acoustic properties of soundproofing materials, I should also mention the noise reduction coefficient and the sound transmission class.
As I have previously explained in my article about acoustic panels, NRC is a helpful scale for determining the amount of noise a product is capable of absorbing. Basically, the scale goes from 0 to 1, with 0 meaning that the product can’t absorb noise at all, and 1 meaning the opposite. Of course, most products fall somewhere in between.
However, as you’ll see in the article I’ve linked to, some products also boast a 1.15 NRC rating, so the scale isn’t always sensible. Also, it’s important to note that a high NRC rating doesn’t necessarily mean that the material will stop the sound from passing through.
STC, on the other hand, does just that. It tells you the sound transmission loss between the source of the noise and the designated area. In other words, a high STC means that the less noise will pass through the material. That’s why the best sound blocking materials have to be thick and have a dense composition.
These ratings should help us determine what the exact capabilities of cork for soundproofing are. Speaking of which, let’s get back to the matter at hand.
Does Cork Have Acoustic Properties?
So what’s the final verdict — should you use cork for soundproofing project? In my opinion, the material could be a pretty useful tool. In fact, it’s more effective than I’d imagined, especially as a natural product.
More specifically, cork is apparently excellent at absorbing the range of frequencies the human voice can make. That’s actually fairly impressive — especially since even noise-canceling headphones tend to have a problem with those sounds.
According to several sources, cork bricks have an NRC rating of about .15, which isn’t exactly a stellar number. Obviously, though, the rating changes depending on the way the specific product was manufactured. When in doubt, you’ll want to go for the thickest product, since that does make it more effective. For example, while a 1/8-inch cork board can cut sound by about 10 decibels, a 1/4-inch board can shave off more than 20 decibels.
However, the material does have other acoustic properties even when you’re using slim boards of it. For example, if you use cork floor underlayment, you’ll find that the material is the perfect padding. That means that it’s great at absorbing vibrations, which is sure to be a relief to your downstairs neighbors.
Other Benefits of Using Cork for Soundproofing
There are plenty of other benefits to using cork-based soundproofing materials, aside from their obvious acoustic qualities. So let’s round them all up. Cork is:
- A naturally sourced Even the adhesive that’s added to the cork shreds to make boards is usually biocompatible to its structure.
- Fairly inexpensive, due to the fact that the cork oak trees are self-replenishing and abundant.
- Very light, since over 50% of its volume is just plain air. That very trait should make it incredibly easy to affix anywhere you want it, though.
- Sustainable and recyclable. If you decide you don’t need your cork insulation anymore, you can just use it for crafts.
- Anti-microbial and water-resistant, making it the perfect mold prevention, if you need to install it in your walls or floors.
- Fire-resistant, to a degree — specifically, to about 390 degrees Fahrenheit, which is its combustion temperature. Apparently, some people have suggested planting cork oak trees in California to prevent wildfires.
All of these advantages bode pretty well for your next soundproofing project, doesn’t it? So let’s answer one last question.
How Can You Utilize Cork in Soundproofing Projects?
Most of the time when people talk about using cork for their soundproofing projects, they are either working on their walls or floors. However, those two surfaces aren’t the only possible areas you can use cork in. Furthermore, even on walls and floors, there are actually several ways to make the most of cork.
For example, I’ve already explained that you could use cork underlayment to soundproof your floors. That would certainly soften and fill up the space beneath your floorboards, making walking on them more pleasant for everyone involved. However, you don’t have to lift your floorboards to soften your floor. You could achieve a similar effect by placing cork boards right under your carpet, instead of getting a carpet underlay.
Similarly, you can use cork both underneath and on top of the drywall. In fact, the cork would probably increase the effectiveness of the thermal insulation of the room, as well. Conversely, you can also use cork tiles on your walls much like you’d use acoustic tiles or panels.
Because cork pin boards are so popular, you can find tiles of all shapes and colors. In fact, many of them have an adhesive layer in the back with a peel-off protective layer. So they’re incredibly easy to install as well.
Moreover, you can also use cork for smaller projects. For example, you can pad the heels of your shoes with it or silence your squeaky bed. You can even use it to construct a soundproof chamber or thicken the walls of your garage studio.
Examples of Cork Acoustic Products
Before I wrap this up, I wanted to leave you with a few examples of the kind of diverse products you might use for your next project.
If you wanted to use a cork underlayment under your floorboards, you could get one of the ones QEP makes. They have a quarter-inch thick one that comes in a 4 by 25-foot roll and a half-inch thick one that comes in rectangular sheets.
Of course, you don’t have to use those products exclusively for your floor. You can also apply them to walls, ceilings, even doors. In fact, I’ve seen similar products that aren’t marketed as underlayment at all. The sky’s the limit.
However, you do have other options for walls and ceilings, at least. Packs of 12 by 12-inch cork tiles are pretty easy to find for pretty cheap. These quarter-inch thick tiles even come in an 80-piece pack. Similarly to the floor underlayment, these kinds of products are available in a half-inch thickness.
On the other hand, if you’d like to play around with the design and placement of the tiles, I might also recommend installing the square ones in a diamond formation. Alternately, if you get these half-inch thick hexagonal tiles, you could arrange them in a honeycomb arrangement.
Final Thoughts on Soundproofing with Cork
If you’ve been considering soundproofing your home with cork, consider this my official blessing. Not only is cork a natural, sustainably-made, and recyclable material, but it’s also the perfect mix of affordable and effective.
Besides, you’ll be able to use it for pretty much anything you can think of. And I even tried to take some of that responsibility off of you by thinking of some things myself. Most importantly, though, cork is exceedingly easy to manipulate, cut, and install — thanks to its lightweight structure. That’s not something you can say for many soundproofing materials, you know!
Cork Production
According to this How It’s Made episode, cork oak trees can live up to 150 years. However, I’ve also found sources stating that they can live even longer than that, with regular harvesting of the bark. In fact, if the trees keep their original bark, their projected lifespan is much shorter, closer to 75 years.
Generally, the first harvest usually happens when the tree is about 25 years old. That first bark can go into flooring or insulation products, while wineries usually wait for the third or fourth bark to use for corks. The bark regrows every 10 years or so, at which point each tree has about 40 pounds of it ready to be harvested.
After the harvest, the bark sits outside drying for a few months. When it’s completely seasoned, they take it into the factory and boil it to make it more flexible. Then it’s out to dry again, during which time the bark expands until air makes up half of its composition.
Several months later, the factory workers saw the bark into strips, and punch wine corks straight out of the bark. Then, the leftover bark goes into a chopping machine, shredding the cork into pieces that are small enough to create a unified paste, with the help of an adhesive. The resulting mixture can be molded into any shape at all, including thin cork boards and insulation materials.
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