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 ongoing backyard test can answer your questions.

If you’re just tuning in to this test, you can find the original article here, and there is a quick recap on the methodology below. If you’re returning to see the results after the last check-in, feel free to skip ahead!

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 difference 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. 

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, Washington. It has been almost a year to this point (February 2021) and the test samples have experienced a full summer of western sun exposure, and a very wet Fall and Winter’s worth of wetting conditions and brief times of freezing temperature. Samples were left against the west side of a wall to receive as much sun and weather exposure 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.

CONTROL SAMPLE

At first glance we can certainly see that the control sample with no paint/stain has lightened in color significantly, whereas the other samples have changed in color much less or not at all.

This demonstrates that it is possible to alter the color of Thermacork with stain, and that paint is definitely a viable solution for completely covering façade cork.

Let’s take a closer look at the individual results.

WATER BASED STAIN

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.

11 Month Results:

This sample has far exceeded our expectations, and after nearly a year in the elements, there is still no appreciable difference in color intensity.

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.  

11 Month Results:

Again, this test did just fine after 11 months in the elements. No discernable differences between this and the pre-treatment sample. We suspect the results from the water-based stain are so excellent because of the very dark color of the stain, lighter stains may result in more sun bleaching of the cork as seen in the following samples.

OIL-BASED STAIN

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.

11 Month Results:

The first 6 months of this test didn’t show much color degradation, and in application pre-treatment and stain went on just as expected. Color change was slight but expected. 11 months in the elements has pushed this color change even further though. While it is still a slight change, it is noticeable enough especially when compared side by side with the original application. The gloss luster of this stain has also faded to more of a ‘satin’ finish.

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?

11 Month Results:

After 11 months, it appears that cork DOES benefit from a pre-treatment before staining.

The color of this sample has become considerably lighter than its original application and is noticeably lighter than its counterpart that did use a pre-treatment.

PRIMER & PAINT

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.

11 Month Results:

Surprisingly, the primer only sample has gotten whiter and appears to have better coverage than when initially applied. We think it might be because the underlying cork has gotten lighter and isn’t showing through the layer of primer as much. Regardless, we still wouldn’t recommend leaving this as a primer only layer and suggest applying a coat of paint as the final layer.

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. 

11 Month Results:  

As expected, this single coat of paint went on thin and resulted in a less than white finish. Applying only a single layer also makes it harder to get into the crags and crevices of the cork for total coverage. Though the paint has stayed on just fine though through the course of 11 months, our recommendation is still to use a layer of primer plus a layer of paint for the best coverage, color fastness, and protection.

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. Brush worked well, a roller with a heavy nap would work well too. The tricky part was getting the paint into the crags and crevices of the cork.

11 Month Results:

This has been the best long-term option to date. 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.

Disclaimer on Impact of Paint and Sealants on Cork’s Vapor Permeability

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 considered 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.

Conclusion and Final Considerations

After nearly an entire year, most of the tests have held up to the sun exposure with minimal or negligible color degradation. Oil based stain without the pretreatment being the outlier here. Again, we recommend using the pre-treatment for better results. The test samples will remain outside through the next year, and possibly longer. If any major changes are noticed, we will be sure to update in a future blog post! Based on the results of this test, we believe that a variety of paints and sealants will work for ThermaCork applications and will provide beauty and longevity for various projects. If you have any ThermaCork projects that have been painted/stained, we would love to hear from you about your experience and how the project looks now.