Artists like to paint on many kinds of surfaces and objects and with many types of media, but the surface or the paint may not be compatible. We understand that most people would not have standard cross hatch adhesion testers at home, so we would like to provide a way for artists to do a simple test to determine if the paint will adhere to the surface or to other layers of paint.
Testing before applying on your final artwork would be crucial. It’s no fun when you spend hours toiling over a painting only to find it has issues later, so doing a test beforehand with the exact materials you plan on using could be a real time saver and save you from heartbreak!
Allowing the proper dry time before doing the adhesion test is also essential, as some surfaces may need more time than others to fully cure, resulting in what might look like adhesion failure at first, but can significantly improve by simply waiting longer. A thin film of most Heavy Body or Fluid Acrylics takes around 3 days to initially cure at room temperature, while a thick film could take weeks or even months to cure depending upon the thickness, the environment and the substrate. A slower drying paint like High Flow and the even slower drying and slower curing paint like OPEN, could take a significantly longer time to see good adhesion. It may also take some more time to see good adhesion on a non-porous surface like Plexiglas® for example. Acrylics dry through evaporation; first the water evaporates, followed by other volatiles, and on a non-porous surface, the only direction for these to evaporate is up. On canvas, however, they could also evaporate through the back. In a very humid environment, it could also take longer for the paint film to dry and cure.
The process is as follows and uses common tools you likely already have in your studio. Make sure the surface being tested is clean and dry. Apply the paints or mediums in the same layers you plan to use on a sample of the surface you plan to use. Allow to fully cure for best results. For a thin film of Heavy Body or Fluid Acrylics, this usually takes about 3 days. You can start the test after 24 hours, then test again at 48 and 72 hours to look for improvement. If you still have failure, then try testing again on a weekly basis if needed, especially on a non-porous surface. Using an X-ACTO® or utility knife, make two cuts in the film, 1.5 inches (4 cm) each that intersect in the middle, in an “X” formation. ASTM (American Society for Testing Materials) recommends that two of the angles be between 30° and 45° as shown in Image 1. Make sure the cuts penetrate all the films being tested and down to the substrate if adhesion to the substrate is what is being tested. Brush away any material removed from the cuts. Use 3 inches (7.5 cm) of masking tape, the off-white kind and not low tack painter’s tape, and apply the tape with the center over the intersection of the cuts and running in the same direction of the smaller angles. Rub the tape firmly with a pencil eraser or the back of your fingernail, but leave one end free. Grasp the free end of the tape and, in one swift motion, pull off the tape rapidly back upon itself, like pulling off a BAND-AID®. It can be helpful to do more than one of these tests on your piece. Determine the level of adhesion by observing the area after tape removal and observing the tape. The best result would be no peeling or removal of the paint. If there is a trace left on the tape in the form of a faint “X”, this would still qualify as good adhesion. Jagged removal along the incisions on either side, would show adequate adhesion. Removal from most of the area of the “X” on to the tape or removal beyond the area of the “X”, is evidence of poor adhesion. If you are testing multiple layers and only one layer is removed, then that would show failure of that layer to the one underneath. Where the failure occurs is very telling.
If you experience adhesion failure, an appropriate primer may be needed as a “bridge coat”, as seen in image 2 where the paint failed on bare aluminum, but adhered well on top of a Direct To Metal primer.
For more information about testing for your application and details about cross hatch adhesion testing, follow this link: https://www.justpaint.org/testing-for-your-application/
As always if you have any questions, feel free to contact our Material Specialists at 800-959-6543 or email@example.com.