Canvas and/or linen have been, and most likely will remain to be a traditional substrate. Unfortunately, encaustic on cloth can flex, causing cracking and chipping. Canvas can be utilized for encaustic works if precautions are taken; however, canvas is not recommended. If you prefer the texture and feel of canvas and are up for the extra work involved in preparation, here is some advice on the subject.Traditionally Stretched: Canvas that is stretched on a frame can and will flex when pressure is applied; most of this occurs during the actual painting process and not as much after the piece is finished (Framing can reduce damage). Slag can also occur, this is when gravity takes hold and the shear weight of the canvas and paint cause the material to weaken over time; thus slag (drooping) occurs. Remembering that more resin introduced into encaustic paint equals harder and more brittle paint, you can reduce the amount of resin by a fraction and this will offer a fraction of flexibility (see How to Make Encaustic Medium and Paint for further detail). However, encaustic hardens over time, so resin reduction only temporarily assists during the painting process.
Prevent the surface from flexing by supporting the canvas; fill the void behind the painting with a hard board or heat tolerant foam. Remove the foam, or board when you are finished or leave it for support. However, time weighs heavily on the surface, regardless of your actions. Remember not to use pre-primed canvas; some gesso's are acrylic based and shrink when heated. However, priming the back of the canvas with gesso, only when finished, can boost the rigidity of the material, but again, time has a way of negating your efforts. Even though traditional stretched canvas can be used for encaustic works, it is not worth the trouble, panel stretched canvas (below) can offer a better alternative- but also has it's issues.
Panel Stretched: Simply stretching unprimed canvas over a wood panel is the best way to go, but really needs to be adhered to the surface. When adhering the canvas to the panel, glue would be ideal, but glue reacts to heat and isn't absorbant. Using the encaustic medium to, "glue," the canvas down is possible, but tricky. Adhesion is necessary to prevent problems like slag down the road. Atop of most reasons to work on canvas, the loss of the surface under the wax often negates most reasons to work on it- purely for the traditional feel. Go to Wood (Includes MDF, Masonite, etc.) under, Substrates and Painting Surfaces, for more information on what type of wood surfaces can be chosen that might better suit your needs. Also a post on the Blog on hardboard, might be of some use.
