Roof Coating Field Adhesion Test (The Castagra Method)
Castagra's Ecodur roof coating has extreme adhesion. Therefore, we do things a little differently than others.
When we first started posting our methods for field adhesion testing on social media, the comments sections blew up. Most people were amazed that we can get legitimate results in under an hour. Others were skeptical about “rapid results” when traditional tests can take 1-2 weeks. A few commenters pointed out that we do not use a traditional 1” strip with the edges cut, and a hearty debate was had. Because of all the interest, we thought it best to address all the questions at once and explain the reasoning behind our methodology.
Even on its worst day, Castagra's Ecodur roof coating outperforms industry standards for roof coatings. Because of this, we have set higher standards for what constitutes a pass for Ecodur.
Also, it should be noted that our adhesion methodology is pass/fail, and for field testing Castagra products only. It Is not the methodology used for regulatory data collection. Many companies use similar field data collection procedures for convenience and consistency. We have conducted multiple tests to ensure that testing our product the way we do is accurate.
Standard Testing Procedure and Misconceptions
Most commonly, critics cited ASTM C 794-01, which is a Standard Test Method for Adhesion-in-Peel of Elastomeric Joint Sealants. It should be noted that even the truest to standard field versions of this test have significant variances from the actual standard method, which requires specific machinery and laboratory conditions. In laboratory conditions, these tests are peeled at a specific rate and exactly 180° using an Instron or similar device.
To attempt to replicate the test in field conditions, the typical procedure is to embed a 1” strip of polyester seam tape between 2 layers of the product being tested. Then, the sample is allowed to fully cure. This usually takes 7-14 days depending on the product. The edges are then cut to eliminate “edge bias” and a knot is tied into the test strip. Finally, using a luggage or fish scale, the sample is peeled slowly at as close to a 180° angle as possible. In field conditions, a true 180° peel as in the laboratory is impossible.
The ASTM standard of a 1” strip was built around existing test equipment and not for a specific scientific advantage. While it is very simple to read the data on a 1” strip (3lbs = 3lbs/lineal inch), it is also easy to read the data on a larger test (12lbs on a 4” test strip = 3lbs/lineal inch). In a lab setting, jigs or masking tape can be used to eliminate edge bias. This is simulated in the field by cutting the edges even with the test strip. When adhesion numbers are marginal, and extreme accuracy is important, edge bias can result in a false positive.
Using a wider test strip with its much higher test loading provides more information about the strength of the layers below the test area. For example, if there is a separation of layers that becomes apparent at 30 pounds vertical force, that would call for additional testing and likely reveal the existing roofing materials are too weak for an effective coating application. Better to find this out sooner rather than later!
The Castagra Method
So why don’t we do things the same as everyone else?
Our way is easier and more accurate.
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- Woven polyester seam tape typically comes in either 4- or 6-inch-wide rolls. By using it as it comes, we eliminate any false readings caused by a strip that is over or undersized.
- Woven polyester seam tape typically comes in either 4- or 6-inch-wide rolls. By using it as it comes, we eliminate any false readings caused by a strip that is over or undersized.
It creates accurate numerical data.
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- A 4x wider test strip reduces the risk of demonstrating a localized effect.
- A wider strip reduces the risk of reading edge bias. Because of our high numbers, edge bias represents a very small percentage of a result anyhow. Using a fish or luggage scale, you are unlikely to see any difference with Ecodur.
It creates better visual data.
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- A larger area gives you more visual information to interpret. This can help detect substrate deficiencies and foreign debris.
- A larger area gives you more visual information to interpret. This can help detect substrate deficiencies and foreign debris.
It eliminates unnecessary substrate damage.
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- Because Ecodur is extremely puncture resistant, it is difficult to cut. Soft coatings are easy to cut with a sharp blade without cutting through the layer below. Cutting Ecodur requires heavy force. The blade is likely to continue through the substrate and additional layers below. This can leave you with repairs to make and cause difficulty reading the results of the test.
- Because Ecodur is extremely puncture resistant, it is difficult to cut. Soft coatings are easy to cut with a sharp blade without cutting through the layer below. Cutting Ecodur requires heavy force. The blade is likely to continue through the substrate and additional layers below. This can leave you with repairs to make and cause difficulty reading the results of the test.
We can do it faster!
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- Ecodur’s unique composition allows us to use an accelerator to get “rapid results” in around 45 minutes. We can achieve pass/fail adhesion results during a roof inspection with no need to schedule a follow-up. This allows contractors to get bids out faster and with fewer trips.
- Ecodur’s unique composition allows us to use an accelerator to get “rapid results” in around 45 minutes. We can achieve pass/fail adhesion results during a roof inspection with no need to schedule a follow-up. This allows contractors to get bids out faster and with fewer trips.
There are also safety concerns.
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- In comparing Ecodur results on near 180° peel vs 90° tests, we see very little difference in results. But, because of Ecodur’s extreme adhesion, it was common to pull a shoulder muscle attempting to peel in the field.
- Ecodur often outlasts the tape during testing. Fist gripping a fish scale while pulling forcefully parallel to an abrasive substrate, like mod-bit, can result in some bloody knuckles when the tape suddenly breaks.
Conclusions
Ecodur’s attributes routinely set it apart from traditional roof coatings. Traditional adhesion testing standards provide a sub-optimum method of measuring a coating's adhesion properties on various substrates. A rapid test using a wider fabric to give much larger pull test numbers provides more precise adhesion data. Additionally, it reveals more about the strength of the layer beneath the test area to the practitioner. As such, Castagra’s standard of 10lbs/lineal inch, or 40lbs for a 4” strip is the new gold standard for the roof coatings industry.
To learn more and for full instructions on setting an Ecodur adhesion test, click here.
Written by: Jef McCurdy
National Training Manager - Castagra
Who Are We?
Castagra is a roof coating manufacturer dedicated to providing sustainable and high-performance coating solutions. Learn more about our products here, or contact our team today to learn more about what we do and how we can help you!
