Should You Heat Cork Before Cutting?
Several online resources suggest soaking or steaming cork to make it easier to cut, especially for projects using wine corks. Heated cork expands and its elasticity becomes more uniform (it normally has elastic anisotropy properties – one directional). This can help provide a cleaner cut and makes sense if you are cutting solid cork.
Cork sheets are made of granulated cork with adhesive. We needed two cork coasters so we tested cutting each of them, one unheated and the other steamed for 15 minutes.
Cutting Unheated Cork Sheets Using Clear Tape On Both Sides Provided Better Results
We found that the best way to cut corkboard sheets to minimize crumbling and get clean edges is to use clear tape and a new Xacto or utility knife. We then followed up with a light sanding using 220 grit sandpaper. See photo at bottom of this post.
The steamed cork sheet expanded about 10% while heated. It also turned slightly darker. It had noticeably rougher edges and didn’t retain its crisp circular lines when it shrank after cooling.
We used clear tape on the unheated cork sheet and found it gave a much cleaner appearance after cutting.
Steamed cork sheet on left compared to using tape on unheated cork sheet on right
What Happens When You Boil Or Steam Cork
However, solid cork does not absorb liquid, which is why it is used for wine corks. Cork has shown to only absorb 3% of water over a 48 hour period. The purpose of the water is that it allows you to heat the cork without drying the cork. When you steam cork, its properties temporarily change.
The downside to heating solid cork is that if heated too long, it can lose some of its natural resins and become brittle over time. The color of the cork can also become darker if heated too long. If you do heat cork, it should not be boiled or steamed for longer than 15-25 minutes.
What Happens If You Boil Or Steam Cork Sheets
As opposed to solid cork, cork sheets are made using small granules of cork oak bark which have been coated with an adhesive and pressed together. Although they are glued together, these very small granules tend to break apart when cut multiple times or using a dull knife.
Heating cork sheets allows the individual granules of cork to expand 5% to 20%, which might provide a more uniform mass for cutting. This effect only lasts while the cork sheet is heated. Once it begins to cool down, it contracts back to its original size.
The downside to heating cork sheets is that you risk removing some of the adhesive that holds the granules together. And once the cork contracts, the cut edges may not be as clean as they were when they were cut.
If You Do Heat Your Cork Sheet
Because the sheet will expand when heated, mark or trace your pattern onto the sheet before you heat it. Otherwise, your project will be smaller after the cork shrinks back to normal.
Smooth Out Rough Edges On Cork With 200 Grit Sandpaper
Fortunately, cork is a wood-based product and can be sanded. If your project has rough edges, you can smooth the uneven cuts with 200 grit sandpaper.