Why We Chose Cork Underlayment & You Should Too
Cork underlayment cannot be beat.
That’s the conclusion we came to after hours of researching every aspect (not just price) of flooring underlayment for a recent project.
Sound & Thermal Insulation
Our project house was located about a mile from a train station. Along with the master bedroom being located above a basement mechanical room. That meant midnight blaring of train horns and water park like sounds coming from the water softener recharging every three days.
Sound reduction was a major goal.
Cork underlayment sound ratings are the second highest right behind rubber underlayment. Rubber is not recommend because it cost more, and is said to emit noxious fumes as it deteriorates over the years. Cork will not deteriorate. Cork naturally contains suberin and ceroids in its cell walls. Allowing it to repel water/moisture, rodents, woodworm, and gases.
What makes cork underlayment so amazing is its millions of air-filled cells. One cubic inch of cork can contain up to 100 BILLION air-filled pockets. Structured in a honeycomb like pattern.
These air pockets help deaden sound from traveling further in ALL directions. This includes outside noise (train horns), and inside noise such as footsteps, music, talking, TV’s, and the dreaded water softener.
STC stands for Sound Transmission Class. It’s a method they use to determine sound traveling through various building components like floor systems, doors, windows, or walls.
Ratings are usually only important to commercial or multi-family dwellings. As most jurisdictions and building codes require a minimum STC rating. Using ASTM testing methods.
Even though not required, these guidelines can give us important information for residential applications.
Most cork underlayment will have a STC score of 50 for 6mm thick (1/4″). If you double the thickness to 12mm (1/2″) you only get 50% of the benefit of 1/4″ with a total STC score of 75.
Meaning 1/4″ cork underlayment provides the most bang for the buck in controlling sound.
If sound reduction is a major goal like ours was…thicker is better. We wanted a maximum cork underlayment sound rating without raising the finished floor too high. So we chose to go with a 12mm thickness.
Be sure to keep floor height in mind. You want space for doors, carpets, floor mats, etc.
Most condo boards require at least 12mm or thicker cork underlayment between floors when using hard flooring. One particular condo story we read stated that after installing 1″ cork underlayment a general contractor could not even hear his crew working on the floor above him.
Conclusion: We felt that the cork did a good job of making foot steps more solid feeling and sounding, quieting the train noises, and the water softener. You can still hear the noises but they went from a ten to a three. Some more insulation and window inserts will be added next to try and get that three to a zero.
Cork is one of the world’s most versatile materials. It’s 100% natural, recyclable, and reusable. Coming from the bark of a cork oak tree (Quercus Suber L.)
A cork oak tree can grow for up to 250 years and is usually hand harvested by a professional in the months of May to August. A total of 17 harvests can usually be completed from a single tree. The first harvest occurs at 25 years, and the second around 43 years. These first two harvests provide the cork used in flooring underlayment, fashion, aerospace, and health industries.
As the cork regenerates it becomes smoother with tighter air-filled pockets. Changing its uses.. such as for wine stoppers that require tighter air-cells.
If the harvesting is done correctly. The tree will not be harmed.
Conclusion: While there is a carbon footprint in all products, cork seems to be once again at the top of the flooring underlayment heap. There was no chemical smells coming from the package or “off-gassing” and it had a nice natural smell.
Cork Underlayment Sheets or Rolls?
We experimented with both cork underlayment rolls and sheets.
If we were to do the job over again we would purchase 1/4″ cork sheets instead of rolls. The rolls are cheaper per square foot. But they require more labor and end up with more waste.
Cracks in between the sheets were solved by staggering the material. That way there would never be a crack straight through the cork underlayment. Allowing sound to transfer.
We installed cork underlyment over lineoleum tiles that were original. The house was built in the 70’s so there was a concern with asbestos if we were to remove them.
Side Note: If your floors are different heights you can also use cork underlayment to level your floor. If one room is 1/4″ higher. Just add another layer of 6mm cork underlay and it will be level. No expensive subfloor work needed.
The slate tiles were not installed correctly. Allowing moisture and water to seep into the 1/4″ wood masonite layer they were thinset onto. The only option was to remove them along with the rest of the floor.
This was more work but in the end provided a seamless installation without any transition strips. Throughout the entire house.
Here is a picture of the kitchen half way completed. We tried to use some duct tape on the cork underlayment to hold it tighter, but found it not to hold. Even Gorilla tape could not hold pieces down for long.
Below is a shot from the master bedroom. We got better at installing the cork underlayment so that tape was not necessary.
Where to Buy Cork Underlayment
We searched our local hardware stores like Menards, Home Depot, and Lowes but where not able to find anyone that had it stocked. Which meant going online.
After searching around we found Amazon had a good deal on QEP brand 6mm cork underlayment in a range of sizes.
What was weird is there is a maximum amount you can buy at one time. (6 rolls I believe.. and I have no idea why this is). We needed around 1600 sq. ft. So we placed two separate orders.
Here is the Amazon link for what we recommend if we could do it over again:
If you are tight on cash and don’t mind dealing the rolls: