Painting and Staining ThermaCork

 Do you have a project that you think would be perfect for ThermaCork, but the only thing holding you back is the color of finished product? If you have ever wondered about the viability of painting, staining, or sealing our ThermaCork Façade panels, hopefully the results of this backyard test can answer your questions. 

The Issue

While ThermaCork makes a wonderful insulator and is a great option for a natural exterior façade, the plain color of it is not always for everyone. When left in its natural state, ThermaCork ranges from a dark brown to a light tan. This color variance comes from natural variance between cork harvests, and from environmental changes in the final installed location such as humidity, temperature, and exposure to sunlight. In fact, it is not uncommon for cork to fluctuate in color as the seasons change. For some people, this is part of the natural beauty and appeal of using ThermaCork.  

All ThermaCork samples after initial stain/painting

Not everyone shares the same tastes though and for some, while the thermal and environmental aspects of ThermaCork are clear winners, the look isn’t exactly what they’re after. To that end, we receive many questions concerning staining or painting the exposed sections of cork. Until recently there were no real-world examples we could confidently point to and could only answer in the theoretical. However, we like to be able to answer customer questions confidently and with real world examples to back it up. To that end, a small test has been conducted to answer some of the common questions surrounding this issue. 

The Test 

To find out how well ThermaCork takes and holds stain and paint, several options were tested. The test consisted of applying exterior latex paint (with and without primer), and stain (with and without pre-stain treatment, both oil and water based) to medium density façade cork samples and leaving them outside exposed to the elements.  

This test was begun in March 2020, in Lacey WA, so to this point (August 2020) the test samples have experienced a short period of wetting and a long period of drying and intense sun exposure. Samples were left against the west side of a wall to receive as much sun as possible.  

Products used: Behr Exterior Latex Paint, Behr Exterior Latex Paint Primer, Minwax pre-stain wood conditioner, Minwax water-based pre-stain wood conditioner, Minwax antique walnut oil based gloss stain, Minwax true black water based solid color stain. All products applied by brush.

This test was begun in March 2020, in Lacey WA, so to this point (August 2020) the test samples have experienced a short period of wetting and a long period of drying and intense sun exposure. Samples were left against the west side of a wall to receive as much sun as possible.  

Products used: Behr Exterior Latex Paint, Behr Exterior Latex Paint Primer, Minwax pre-stain wood conditioner, Minwax water-based pre-stain wood conditioner, Minwax antique walnut oil based gloss stain, Minwax true black water based solid color stain. All products applied by brush. 

Water Based Stain with Pre-Treatment

Initial thoughts:
Based on the hydrophobic properties of ThermaCork, we did not expect water-based stains to work all that well. The pre-stain conditioner went on and soaked in as normal though, and the stain applied without issue. After drying for the recommended amount of time, this sample was placed outside and left in the same spot with periodic checks.

Results: Surprisingly, this test sample did just fine after nearly 5 months exposure to sun and rain. There has not been a significant decrease in the color intensity of the stain, and it held up to gentle spraying of water to remove pollen. 

Water-Based Stain without Pre-Treatment 

Initial Thoughts:
As with the previous test, we expected less than stellar results with a water-based product, especially without the use of the pre-treatment. As before however, the stain applied just fine, with maybe a little more effort or a second pass being necessary to attain even coverage, but not significantly different from the test that included pre-treatment. 

Results:
Again, this test did just fine after 5 months in the elements. No discernable differences between this and the pre-treatment sample.

Oil-Based Stain with Pre-Treatment 

Initial Thoughts:
Oil based products are what we typically recommend to customers looking for a way to change the color of their cork facades. Because of cork’s natural property of absorbing oil, (some places use bags of cork granules for their absorptive properties!) the expectation is that cork will more readily accept these types of stains. 

Results:
No surprises here. Pre-treatment and stain went on just as expected. Color change was slight, but expected because of the minimal difference between the cork’s original color and the walnut stain. However, the resulting color does have more “depth” and warmth, though this could be very subjective. After six months of exposure there has been no degradation of color and the ‘gloss’ finish retains it’s luster.

Oil Based Stain without Pre-Treatment 

Initial Thoughts:
This test sample was expected to be very similar to the previous sample. In fact, it was exactly the same in application and result. It appears that pre-stain might not be necessary for cork? 

Results:
Just like the oil-based stain with pre-treatment, this performed perfectly fine without a problem. 5 months in and it has held up just fine.

One Coat - Primer Only 

Initial Thoughts:
Primer is not usually left as the exposed coat, but we wanted to cover all the bases and left this section to be a single layer of primer. Not much was expected of this test, and the single layer of white primer did not turn out quite fully white, with much of the brown cork still discoloring the primer. 

Results:
So far however, the primer has held up just fine, if maybe a little more yellow than it started out.

1 Coat Primer + 1 Coat Exterior Latex Paint 

Initial Thoughts:
This combo is expected to give the best coverage, protection, and color longevity. Applying this combo was just like painting wood. 

Results:
This does seem to be the best long-term option so far. Color has not faded; paint has bonded nicely to the cork and is not flaking or chipping.

The coating of latex paint also seems to have added some extra protection to the cork by preventing tear out and impact damage.

One Coat Exterior Latex Paint

Initial Thoughts:
This test sample is to represent the ‘quick’ solution of just slapping a coat of paint on and calling it good.  

Results:
As expected, this single coat of paint went on thin and resulted in a less than white finish. The paint has stayed on just fine though through the course of six months.

Conclusion and Final Considerations 

After nearly six months, all the tests have held up to the sun exposure. The test samples will remain outside through the fall and winter to assess the effect rain and freezing weather will have, and there will be an update article to go over those results. Based on the current results however, we are thinking they will all hold up just fine. 

Paint Coverage Requirements

Because cork is naturally porous and irregular in shape, consider using a thicker nap with your roller, this will help the paint get in to the small crevices and surface voids on the cork panel’s surface. Darker paint colors will require less layers, and darker stains will have a more dramatic color change effect. Lighter paint colors will require more layers to achieve complete coverage and even color. No lighter stain colors were tested, but another test is in the works to see if it is possible to lighten the cork naturally in the sun and then seal it to ‘lock’ it in that color phase.  

Impact on Cork’s Vapor Permeability

Finally, it is important to note that any of these treatments has the potential to impact the vapor permeability of the cork. If part of your reason for using cork includes that vapor permeability, then you might want to reconsider using paint or stain. Latex paint especially will severely inhibit cork’s ability to dry outward and should be taken into account for any planning. If that is not a factor though, then by all means, paint your ThermaCork any color you see fit, and as always, we love seeing your projects so send us photos of your bright pink cork wall. Remember to check back in another six months to see how this test progresses.