From the Ground UPFebruary 27, 2013
Much like building a home, creating a solid foundation for your artwork ensures the structure is well supported. Without this preparation, not only is the final look of the work potentially affected, but the foundation itself can cause and hasten its breakdown.
In painting, a carefully prepared surface helps seal the support material from the paint layers, ensuring that issues of support induced discoloration (from the natural acids found in wood stretchers and surfaces) or possible canvas rot do not eventually effect the look of the finished work or its structural integrity. A well prepared surface also helps your chosen medium bond well to the substrate beneath it and prevents unnecessary loss of paint through absorption into the substrate material.
Selecting the right type and combination of foundation layers begins with the your personal preference of the kind of support you wish to paint and your painting media. Time spent in preparation can be the difference between your painting lasting decades or centuries. Continue reading for a primer in surface preparation and visit your local Opus for assistance in choosing the right combination for your next piece.
Preparing Canvas Surfaces
Whether you have opted for cotton, linen, a pre-stretched primed canvas, or selected a raw or pre-primed canvas to stretch yourself, ensuring the fabric is properly prepared for your preferred media is essential.
With raw canvas, the ideal first step is a base layer of size. Sizing coats the raw fibers, functioning as an isolating layer for fabric supports, helping to prevent surface induced discolouration and canvas rot. While Rabbit Skin Glue has been used traditionally, most contemporary artists use polyvinyl acetate (PVA) size or acrylic mediums like Golden GAC 400 rather than traditional sealants as they resist humidity and are more dimensionally stable. If you want the fabric stiffening properties of Rabbit Skin glue, use GAC 400 on your raw canvas before applying PVA or Golden GAC 100.
After sizing, or sometimes in place of size, acrylic gesso is applied to further seal the surface and prepare it to properly receive and bond with the layers of paint that will be applied over it. Without gesso, the paint would absorb directly into the permeable canvas. Not only is this a waste of your colours but oil paint applied directly to canvas will contribute to canvas rot. Gesso also gives the surface more tooth, helping with paint adhesion for both oil and acrylic.
If you want to prime your own stretched canvases, there are various grounds and materials to choose from or experiment with: Acrylic Gesso, Oil Ground, grounds for watercolour (Absorbent Ground) and pastel (Ground for Pastel).
Acrylic gesso is the most commonly used primer for both acrylic and oil paints and is the product used on most pre-stretched canvases available for purchase. Acrylic gesso is the best ground for use with acrylic paints, but can also be used as a ground for oil paints provided at least 3–4 coats of gesso are applied to the painting surface. This is an especially important step if a size was not first applied to ensure the oil does not leach through to the canvas layer. It is a great all-purpose primer that will stick to almost any surface that is free of oil, grease or dirt, and is non-toxic, safe and easy to use.
Palette knives or plastic trowels are ideal for thick gesso and creating texture effects. However, the most common way to apply acrylic gesso is with a wide flat brush. The first layer of gesso can be thinned with up to 25% water. It helps to wet the brush in water first as this aids with the flow and ease of application.
Once the gesso is dry, you can lightly sand it using a fine grade sandpaper and apply a second coat, moving in the opposite direction as the first layer. Two to three coats of a professional grade gesso is usually sufficient, but additional layers can be added, following the same procedure. You may also choose only to sand after the last layer of gesso is dry as a final step to a smooth surface.
If you wish to increase flexibility and lower the tooth and absorbency of acrylic gesso, you can add acrylic gels or mediums. To increase tooth or alter the texture of acrylic gesso, molding pastes or other coarse gel mediums can be added. The addition of these products will produce a thicker gesso, which may require a palette knife or colour shaper to apply the mixture.
For further tips on preparing your surface with acrylic size and gesso, watch our How-To Video: Surface Preparation: Sizing & Gesso
Oil ground is a solid coat of white oil paint specially formulated to act as a ground upon which subsequent layers of oil colour will adhere. For gessos or grounds designed for oil painting, the material is applied in thin layers with a palette knife or trowel and then evened out using a brush. If the gesso or ground is too thick, a small amount of professional grade solvent (5%) may be added before applying. The surface should be set aside to dry overnight before additional layers are added, though usually two coats of a high grade gesso or ground is sufficient. Allow the surface to dry for several days before you begin painting.
Preparing Wood Surfaces
For the same reasons as canvas, wood surfaces should also be prepared to accept the your medium of choice.
If necessary, you may lightly sand your unfinished wood surface to remove any splinters or small imperfections. Then, wipe the surface down with a slightly damp cloth to remove sawdust or grit on the surface. Sizing is then applied, which in addition to discouraging support induced discoloration, it also helps to prevent possible warping when water-based media is used.
Apply two of coats of PVA size or acrylic medium (Golden GAC 100 is recommended) to the entire panel, front, sides, and back to seal the wood permanently. It will be the first layer of protection on the front, and a barrier against moisture penetration on the back, and will also keep the wood from absorbing large amounts of your paint.
Once your sizing is complete, you are ready to apply gesso (using the same application methods as described in Canvas Preparation). Gesso adds tooth to the surface, helping subsequent layers of paint adhere to the wood. Before applying the gesso, you can cover the sides with painter’s tape to keep the edges clean.
Acrylic gesso is generally used for both acrylics and oils. Gesso is most often white in colour but, depending on the media you will be using and what effects you are looking for, there are other options. If you wish to keep the wood grain visible, try using a clear gesso. You can also tint your white and clear gessos with pigment or paints (such as Golden Fluid Acrylics) to set the right tone for your work. Black gesso can be striking choice as well.