MITRA Forum Question Details

If you read through our “resources section” and do some relevant searches, you will see that we have discussed most of these issues. Even so, here are a few thoughts: I do not recommend plywood panels for traditional gesso, chalk glue grounds, or acrylic dispersion grounds without some sort of interleaf, preferably of fabric. For 25 years I have seen the surface of panels created by very good craftspeople exhibit checking along the grain with all of these grounds (do a search here to find more discussion of this).

Additionally, I see no reason to use an acrylic dispersion medium under an animal glue/chalk or calcium sulfide ground. The ground negates any of the stability benefits of the size and creates a situation where the more brittle layer is over the more flexible one. I would size with animal glue if intending on using an animal glue bound ground.

Please peruse the site but also feel free to ask any additional query on that, or any other, subject if you feel that we have not covered your particular question.

​Just wanted to add some notes as our GAC 100 was referenced. First, we would not recommend any acrylic medium under a traditional gesso, hide glue/ chalk ground. The adhesion is just not ideal as those grounds really need a very absorbent surface to lock into. So would definitely follow Brian's recommendations on that.

Second, just to clear up the role of GAC 100 as a "sealer" as it is being too often misunderstood. GAC 100 will NOT 'seal' a panel off from moisture or humidity, which are really the things you want to control. In fact acrylic coatings score quite low in terms of providing an effective barrier to moisture. However, GAC 100 or Gloss Medium are used to block something called Support Induced Discoloration, but that is only a concern for acrylic paints working in specific ways. In your case, having GAC 100 on the sides and back would at most provide a physical barrier, but being as soft as they are, they will also easily become dirty. Instead, if wanting to truly seal a panel from changes in humidity, we would recommend using 2 coats of an exterior alkyd-based wood primer, and if wanting the ultimate moisture seal, follow that with a paint made with aluminum flake. Most major manufacturers such as Sherwin-Williams®, Benjamin Moore®, PPG®, and Rust-oleum® produce these, where they are commonly used for marine, metal, or automotive applications.

For an excellent list of the coatings with the best ratings for moisture-excluding effectiveness (MEE), we would recommend looking at the table on pages 13-15 in Williams, R. Sam's “Chapter 16: Finishing of Wood”, Wood Handbook, Madison, WI, Forrest Products Laboratory:

 http://www.fpl.fs.fed.us/documnts/fplgtr/fplgtr190/chapter_16.pdf

As always hope that helps clarify things.

As oil grounds are, at least initially, more flexible than glue grounds they probably fare better…..at least in the short term. Again, however, I really do not recommend plywood substrates for oil painting grounds without an interleaf.