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Encaustic adhesion: classic pitfalls & tips

Encaustic adhesion to the substrates (or the lack of it) is a mayor issue in the encaustic practice. On the one hand the encaustic practice is very new. On the other hand mix-media and new materials are very tempting to artists always looking for new challenges. On top of it  there is practically no information about this issue. If you are one of the pioneer-artists looking for new materials at the bottom of the page you will find an easy encaustic adhesion test (that you will 😍…).

The encaustic medium versatility makes the encaustic technique very tricky if you don’t know what all this “encaustic adhesion” is about.

Encaustic durability: What you need to know

Encaustic durability is directly related to:

• Lack of adhesion to the substrate (delamination)
• Lack of cohesion (lack of adhesion between wax layers)
• Stresses as consequence of extreme temperatures during transport

 

 

We will review three mechanisms that have great impact in the material failure

Adsorption – wetting or sizing

The adhesion results from the molecular contact between two materials that make intimate (molecular) contact with the substrate.

The process of establishing continuous contact between a liquid element (wax in our case) and the substrate surface is known as “wetting.” The figure below illustrates good and poor wetting. Good wetting results when the wax flows into the valleys and crevices; filling pores, holes, crevices and micro-voids on the substrate; poor wetting results when the wax bridges over the surface irregularities.

Chemical Bonding

Certain binders (like casein or hide glue) have a functional group that can chemically bond wax molecules more tenaciously. These strong and durable bonds require close contact (or adsorption) of the wax on the surface followed by a chemical reaction.

Mechanical Interlocking

This adhesion results from forces developed by the wax penetrating the irregularities on the surface, displacing the trapped air at the interface, and lock-on mechanically to the substrate.

Mechanical adhesion develops in two ways: First, the irregularities increase the total contact area between between the wax and the substrate over which chemical bonding can develop. Second, The irregularities give “tooth” to the substrate. See image below.

Another benefit of mechanical interlocking is that a rough joint will provide a thermal stress (due to extreme temperatures) propagation barrier preventing an accidental fractures and spliting during extreme weather conditions and thus increasing encaustic durability.

 Tips to improve encaustic adhesion = encaustic durability

Good encaustic adhesion results when the following occurs:

When  the wax flows freely over the substrate and make intimate contact with the substrate.

• By cold weather always warm the panel with the heatgun or over the heated palette (to body temperature) before sizing
• Let the brush stand 3-5 seconds in the encaustic medium between strokes
• Fuse thoroughly with the second layer, give special attention to the sides.
• By cold weather before applying new wax to an already sized panel, wipe the wax surface with a clean paper towel and warm the existing wax layer to body temperature before applying a new layer on top,
• Do not forget to fuse all layers.

When chemical bonds are formed at the interface between the wax and the substrate

• If you use gesso you can use casein or hide glue gessoes, since they build chemical bonds with the wax.

When the wax penetrates the roughness on the substrate surface, resulting in mechanical interlocking once the wax cools

• If you make your own gesso you can use crushed fillers, instead of chemically precipitated ones, to increase the interlocking effect.
• If you paint directly on the wood, you can crosshatch with a cutter the surface

 Acrylic  gesso for encaustic

The total adhesion between materials is the sum of all three forces, you may use acrylic gesso for instance (does not bond chemically) provided you increase the adsorption or the interlocking effect.

You can find how to modify an standard acrylic gesso to make it suitable for encaustic in one of our recipes. Below you can register to access the downloadable files.

Encaustic adhesion test made easy

If you want to know if an specific material is adequate for encaustic you can try the following:

1. Make a small sample of the new substrate you want to test
2. Apply the 2-3 wax layers as you would do normally, wait 3-4 days (better if cold)
3. Cross-hatch the surface every centimetre with a cutter
4. Apply wide cello tape assuring perfect contact to the wax
5. Peel vertically in one only movement

Analyse the results

• No peeling or trace peeling – excellent
• Removal only along incisions – acceptable
• Removal from most area – unacceptable

 

If you want to download the Porous acrylic gesso recipe please sign up for the Modernist Encaustic Club

This post is also available in: Spanish