Adding to Your Gesso

Q. I’ve recently started painting on panels of untempered masonite coated with a gesso ground, but while the first coat of gesso was still wet I pressed on a layer of screen-strained sawdust. Then I let it dry, sanded the surface, removed all the loose dust and applied a final coat of gesso. Can an oil painting on this kind of ground be considered permanent?
William J. White
Monticello, KY

A. If I can assume you’re using acrylic gesso rather than traditional glue gesso, then the addition of any material not already in the manufacturer’s formulation can upset the balance (pigment-to-binder ratio) of the ground. That means that your ground layer might not provide a proper ground for your oil paint, leading to problems such as flaking, poor adhesion, and uneven absorption of the paint, which leaves an uneven gloss on the surface. For a specific example, an unbalanced ground layer can pull the binding medium from the initial paint layer, leaving the paint’s adhesion very lean and leading to flaking.

Sawdust absorbs and expels atmospheric moisture (it’s “hygroscopic”), and such materials are a particular concern because they’ll draw water from the surrounding acrylic binding medium and may cause those areas of paint to be underbound. The sawdust will also trap the moisture, holding water in the ground film longer that the normal drying time. In short, with the addition of sawdust I don’t think you’ll have a sufficient or permanent ground for an oil painting.

If you’re looking for more texture underneath your paint, some manufacturers make materials like powdered marble that can safely be added to the ground, but be sure to check with the manufacturer of the gesso for its recommendations about what’s compatible. When adding these texturizing materials, make sure they’re thoroughly mixed into the acrylic gesso to ensure that each particle is adequately surrounded by the binder. But they’re likely to cause your gesso to thicken, and in this situation you’ll have to be careful to avoid the common mistake of adding too much water in the effort to create a more brushable consistency. This would bring up the problem I mentioned earlier of throwing the pigment-to-binder ratio out of balance.

A painter for more than 20 years, Donald Clegg has been part of 100-plus juried and invitational exhibitions, including those of the National Watercolor Society, the Northwest Watercolor Society and Watercolor USA. He’s a signature member of the National Watercolor Society and has received many awards for his watercolor, oil and egg tempera paintings. He lives in Spokane, Washington, and travels to fine-art fairs across the country.

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