What You Should Know About Cork Flooring
Cork was first used as a floor covering in the early part of the 20th century, although its use fell off by about the 1960s. Cork has been making a comeback since the start of the 21st century, largely because it’s considered “environmentally friendly.” No trees need fall to harvest cork. It is derived from the bark of the cork oak tree. After it is stripped from the tree it re-grows approximately every nine years. Portugal has long been the largest producer of cork followed by its neighbor, Spain, and several other countries in the Mediterranean region that have vast cork forests. The most widely used cork product, of course, is the one that ends up in a wine bottle. The cork that’s unsuitable for bottle stoppers or left over from their production material is used for many other purposes. A lot of it is ground into particles and compressed under heat and pressure into blocks. This material, known as agglomerated cork, is sliced into various thicknesses depending on the product being manufactured. Gaskets, expansion joints, shoe soles, bulletin boards, floor coverings, and many other materials are made from agglomerated cork. What else makes cork so desirable? It has a unique cellular structure that is at least 50 percent air. As a result, cork is a good choice for flooring. It is a natural heat and sound insulator and has softness underfoot that is unique to this material.
What are the different Types?
Cork tile, as described in ASTM F3008 is manufactured either as homogeneous, with the pattern and color all the way through the tile or heterogeneous (veneer), where the visual is only on the surface. The advantage of homogeneous products is that they can be sanded and refinished when the floor gets worn or damaged. Veneer products, as beautiful as some of the patterns are, should not be sanded and refinished. However, in light to moderate traffic, veneer products should stand up fairly well if they are properly maintained.
Where can cork flooring be used?
Like wood, cork is not ideal for every location. The two areas I am most cautious about are very wet areas and in direct sunlight.
- Like any natural material, cork can fade under a lot of sun. If it happens, homogeneous cork can be sanded and refinished, but it’s best to prevent damage by using window coverings.
- Though cork has good resistance to water (think about a wine bottle cork), if it takes on a lot of water the overall integrity of the installation can be compromised because the adhesive can let go. The best (or worst) case I saw of this was a café in Manhattan where cork was installed. You walked right off the sidewalk onto the cork floor; no vestibule, no walk off mat, and the rain and snow and mess of New York City tracking on the floor. The owner was wet mopping the floor to boot. It didn’t have a chance. On the other hand, I saw cork in the bathroom of a hotel guest room and it was in perfect shape. The difference was that the hotel had added several coats of extra finish to the floor after installation so it had a lot more protection. Like wood, cork needs to be used where it will not be abused and where it will be maintained correctly.
How is it installed?
The traditional method uses water based contact adhesive applied with a paint roller - to the back of the tile and to the substrate. Contact adhesive for cork has been in use in Europe for decades, and most North American based cork companies have also used it. This sounds like a pain in the neck at first but is not as time consuming as you might think, especially since you can coat the tile a day before installing it and some products have it pre-applied at the factory. The advantages to contact are that it is spread with a paint roller, which gets the installers off their knees. You can coat large areas of substrate at one time, and it creates instant bond. There are rarely any curling edges, you can work on top of it and walk on the floor as soon as it is installed. I have spoken to many installers with a lot of years of cork installation experience and many of them prefer contact to any other method for these reasons. I am really not a fan of trowel-applied adhesive for cork tile. It’s a wet set, which is very slow, you can’t work on top of it and it’s easy to leave too much open time that leads to bond failure later on.
The first step is to coat the tile. If you do it the day before, one installer works on floor prep, another installer or helper can set up in an adjacent area to coat the tile. Make sure to cover all the way to the edges! Once the adhesive turns completely clear (about 30-45 minutes), it is dry and you can stack the tile (face to back, not back to back!) or put it back in the box. Right before you are ready to install the floor, make sure the substrate is clean, dry and smooth, strike your lines and apply the adhesive using a paint roller. When it’s clear and dry to the touch, you are ready.
Lay the first tile in place, tap it with a rubber mallet and continue. The tiles can be laid snug up to the adjacent tile and set into the adhesive so the tiles are tight up next to each other. It almost sounds like a “zip” plastic bag when you slide it into place. Then, tap the tile with a rubber mallet. You don’t have to hit it real hard – just a firm tap all around the edges and in the center to be sure the two adhesive films are in contact with each other. You can also follow up with a 100 lb roller if you like. I prefer the mallet method to a roller alone, but doing both is also a good idea.
What about site conditions?
Like wood, cork is subject to changes in dimension due to temperature, humidity, and moisture. If the building is not yet enclosed with heat or AC running, don’t do the job. It should only be installed after the other trades are finished to avoid the possibility of damage to the floor. Substrates need to be dry, flat, smooth and clean. Prepare and test concrete according to the manufacturer’s guidelines and ASTM F 710, Standard Practice for Preparing Concrete Floors to Receive Resilient Flooring. This means moisture testing of concrete slabs, and proper preparation to be sure you have a flat and smooth substrate. Have the material delivered to the job site at least three days before installation to make certain it can acclimate to job site temperature and humidity. Having it in your warehouse and then bringing it to the job site does not count.
What about finishing and maintenance?
Most products being sold today are factory finished with several coats of water-based polyurethane. Unfinished cork or factory waxed cork are the other two options.
To maintain urethane-finished cork floors, damp mop with the recommended cleaner. Avoid the “mop and a bucket” method used for other resilient floors. Think wood, and a “damp” cleaning method, not wet.
It’s a common practice to add an additional coat or coats of urethane to a new cork floor. This is the same procedure as for an older floor that’s getting a little worn. Use a cork-specific urethane and a “screen and recoat” process as would be done on a urethane finished wood floor. Generally you’d want this done by an experienced “sand and finish” specialist.
How do you handle unfinished cork? Like unfinished wood. It must be finished before the floor can be used and it can also be stained to create a unique color. For companies that do a lot of “sand and finish” work for wood floors, this is a great way to go with cork too. It results in a smooth, flat and tight floor.
Wax cork is the “old fashioned” way; it has a beautiful patina, but can be a challenge if the maintenance team doesn’t know how to paste wax a floor. This is not the same as acrylic finishes used on other resilient flooring, which are often called “wax” but are actually a mop on finish. Paste wax is a completely different process.
What about Cork floating floors?
Engineered plank flooring with a core of high density fiberboard (HDF) is installed using the same methods as other floating floors like laminate and engineered wood or bamboo. The substrate needs to be flat and fairly level, and expansion space needs to be allowed for at the perimeter, in doorways, and in the field too on areas larger than about 1500 square feet or so, depending on the manufacturer’s specifications.
What about Cork-Rubber or Rubber-Cork floors?
There are a number of products that mix rubber and cork and there are some very confusing marketing terms being tossed around. I have seen products claiming to be 60% cork — true when calculated by the overall volume, but by weight, they are less than 10% cork because cork is lighter than rubber. So the proper term should be Rubber-Cork. This is rubber flooring with cork in it, not the other way around. Rubber-Cork floors get installed like a rubber floor, usually with a wet set adhesive that is spread on the floor, not by using contact adhesive as you would on cork tile. So, these are really rubber floors when it comes to installation and maintenance.
As far back as the 1920s, millions of square feet of cork flooring were installed in North America, but cork use fell off as other synthetic materials grew in popularity. For the past 15 years or so, cork has reemerged. As cork flooring continues to grow in popularity, professional flooring contractors who understand this product can become cork specialists. They will be the ones who get the jobs while others who are intimidated or unfamiliar with this beautiful, environmentally friendly material don’t.