What is Gesso, Size and Ground?

by Ben Platt October 28, 2021 5 min read

What is Gesso, Size and Ground?

Painters have been priming their supports (canvases, boards, wooden panels etc.) since time immemorial to make sure the paint they are using stays where it is put.

In this article we will be giving you a brief overview of the materials and reasoning behind priming surfaces for painting. We will cover the basics of sealing a surface, using a primer or gesso, discuss the use of grounds and cover some of the materials available.

Size and Sealing

Size is the term used for a glue or medium used to seal a support to prevent the paint layers from absorbing directly into the support itself. It creates a non-absorbent barrier between the support and the paint going onto its surface. Mediums often used as size include acrylic polymer mediums, PVA glue and rabbit skin glue (sometimes called hide glue). Each is highly resistant when completely dry and reduces absorbency although rabbit skin glue is only suitable for oil painting and is not pH neutral, so is advised against by conservationists.

Liquitex Professional Matte Medium - 237ml

When using unprimed canvas it is advised that the canvas be sized prior to application of any further surface preparations. It is also recommended to size wooden panels and boards before painting directly to prevent moisture absorbing into the wood and causing swelling and potential splitting. In the case of oil paint, sizing a wooden panel prevents moisture or any residual acids in the wood from seeping up into the paint layers.

When it comes to application, size should be applied in at least two thin coats across the entire surface of the support to ensure a complete seal.

Gesso and Primer

Traditionally Gesso was a mixture of gypsum plaster and chalk mixed with water and other binders to make a white slurry that creates an absorbent surface for painting on. Contemporary mixtures still keep the name gesso but tend to be made with acrylic polymer, pigment and a particulate to give the finish some tooth. Gesso is sometimes called Gesso Primer or Gesso Ground, primer tending to be more fluid and ground comparatively thicker, but this is not a definite rule. Most acrylic gesso can be sanded between coats with a fine grit sandpaper for a smoother finish, but remember to wear a dust mask when doing this.

Galeria White Gesso Primer - 1 Litre

Apply gesso with a large flat brush or painting knife for a smooth application, applying at least two thin layers, one going from top to bottom and another going from side to side to ensure the best possible coverage. Leave to dry for 24 hours at least, but this may vary depending on how thick the application is and how many layers have been applied.

Primer, generally speaking, is a catchall term for a medium specifically formulated to provide a good stable surface with strong adhesion for paint which includes gessoes, as a rule of thumb. 

Spray-on primers are produced by spray paint manufacturers such as Montana who provide a range formulated for use on a multitude of surfaces. Spray primers are easy to use and apply quickly from the can and dry within a day. This makes them useful for priming large surfaces and 3D objects swiftly, with little hassle.

To use a spray primer consult the directions for use on the side of the can. Wear a dust mask or spray in a well ventilated area (preferable outside) and much like the brush technique, go up and down and side to side to guarantee the best results.

A note on gesso and size. When using a brush on gesso it is not necessary to size the support as the gesso itself contains an acrylic polymer that seals the surface it is being used on. Gessoes nowadays are made with the convenience of the artist in mind, but this does not prevent the artist from sealing their support with a size should they desire.

Restored gesso panel representing St. Martin of Tours

Restored gesso panel representing St. Martin of Tours. From St. Michael and All Angels Church, Lyndhurst, Hampshire. (Image source - Wikipedia)


Ground is the term for medium applied over size or gesso as a “ground layer” or foundation for the rest of the painting. Ground is sometimes necessary to achieve certain painting techniques, for example a highly fluid ground such as the Bob Ross Liquid White provides a wet surface for using ala prima (wet-on-wet) oil painting techniques.

Bob Ross Base Coats

Some products are specifically called “ground” but various mediums can be used as grounds. Texture paste, black lava gel, sand gel and other kinds of pastes can be used as grounds for paintings.

In short, ground is a surface preparation that does not seal the support so should be applied over a size or gesso if a particular finish is needed.

Apply as required using a large brush or painting knife for smooth application or work less precisely for a surface with texture.

Sizes & Sealers, Gessos and Grounds

Mod Podge Matt - Mod podge is a high quality PVA medium for use as an all purpose adhesive and sealer, great for making top coats for craft projects and perfect for use as a size in sealing both canvas and wooden panels. It comes in 3 finishes, Gloss, Satin and Matt and we suggest using the Matt as a size.

Golden GAC 100 Acrylic Primer and Extender - A useful multi-purpose fluid medium that can be used to extend and thin acrylic paints, or mixed with dry pigment to make acrylic colour. The fluidity and flexibility of the acrylic film makes it a suitable size for canvas and wooden panels alike.

Daler Rowney Graduate Gesso - An economically priced acrylic gesso suitable for use as a primer for acrylic and oil colour. Available in 2 sizes and ideal for providing a solid and absorbent base layer for painting. Great for students or for when bulk is required.

Winsor & Newton Professional Acrylic Gesso -This artist quality artist gesso has been formulated for superior absorbency as well as superior coverage. The white gesso will prime and seal in just one coat but two thin coats are recommended. Also available in a clear, unpigmented gesso, it can be applied to keep the original surface below visible through the primed layer or it can be mixed with acrylic colour to create a base coat for a painting.

Daler Rowney Texture Paste - A heavy bodied acrylic paste with a slightly sandy consistency which provides an excellent tooth for painting on. Applications will retain bush marks and shape and it is ideal for adding texture to a painting's base layer.

Michael Harding Foundation White - Created to be fast drying and a highly opaque foundation layer for oil paintings, it can be applied over acrylic gesso or a sized support. Mix with a small amount of turpentine for a smoother finish if needed.

Bob Ross Liquid White -A linseed oil and Titanium White oil colour mixed to a fluid consistency perfect for facilitating ala prima (wet-on wet) oil painting techniques. Apply a single thin coat evenly across a primed canvas or board for a slick surface which allows for quick and clean blends when working in Ross’ style.

GOLDEN Absorbent Ground -This viscous acrylic medium dries with a highly absorbent finish with a quality similar to that of watercolour paper. This surface allows for watercolours and gouache to be used on primed canvases and wooden panels, and also makes for intense staining effects when used with acrylic ink or fluid acrylics.

Ben Platt
Ben Platt

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