If you are here because you own a paint by numbers kit, the answer is no. Do not put gesso on it. The canvas arrives already primed, and the numbers and outlines are printed on top of that priming. A coat of gesso would cover the very thing you need to see. There is nothing to prepare and nothing to buy.
If you are here because you are priming a raw canvas, a board or a panel of your own, the rest of this page is for you.
What gesso actually is
Gesso is a primer. It sits between the surface and the paint, and it does two jobs: it gives the paint something to grip, and it stops the surface absorbing the paint unevenly.
The word covers two quite different materials, which is where most of the confusion starts.
Traditional gesso
Animal glue, usually rabbit skin, mixed with chalk or gypsum and a white pigment. It is brushed on warm, in many thin coats, and sanded to a surface like polished bone. This is what medieval and Renaissance panel painters used under tempera and gold leaf. They worked in two grades, a coarse gesso grosso first for the bulk, then a fine gesso sottile for the finish.
It is beautiful and it is brittle. Traditional gesso belongs on a rigid panel, because on a flexible canvas it cracks the first time the fabric moves. That brittleness is precisely why it was replaced.
Modern acrylic gesso
Almost everything sold as gesso today is not gesso at all. It is an acrylic primer: an acrylic polymer emulsion carrying titanium white and a chalk filler. Keeping the old name is a convention rather than a description.
What matters is that it stays flexible when dry. That is what lets it work on stretched canvas, and it is why a modern canvas can be rolled in a tube without the priming cracking. It also dries in under an hour, cleans up with water, and costs very little.
Do you actually need it?
It depends entirely on what you are painting on.
- A pre-primed canvas from a shop. No. It already has two or three coats of acrylic primer on it. Add more only if you specifically want a smoother surface.
- A paint by numbers canvas. No, emphatically. See the top of this page.
- Raw, unprimed canvas. Yes. Bare canvas is extremely absorbent and drinks the binder straight out of your paint, leaving a dull, sunken, blotchy surface. Some artists want exactly that staining effect, but it is a choice rather than a default.
- Wood, hardboard, MDF or paper. Yes. These are absorbent, unevenly so, and gesso evens them out.
- Oil paint on anything raw. Yes, and this one is structural rather than cosmetic. The acids in drying oils attack cellulose fibers, and over decades an unprimed canvas painted in oil goes brittle and disintegrates. A primer between the two prevents it.
Applying it properly
Gesso rewards thin coats and punishes thick ones. A single heavy layer dries with brush ridges and skins over on top while still soft underneath.
- Stir it. It settles in the tub, and the pigment sits at the bottom.
- Thin it if it is stiff, with water, a little at a time. You want the consistency of thick cream, not paint and not paste.
- Apply a thin coat with a wide, stiff, flat brush, working in one direction across the whole surface.
- Let it dry completely. Touch-dry is not dry. Acrylic feels dry long before it has cured, and sanding it early just gums up the paper.
- Sand lightly with fine paper if you want smoothness, and wipe the dust off with a barely damp lint-free cloth.
- Apply the next coat at right angles to the last one. The cross-hatching is what evens out the coverage.
- Two coats is normally enough on canvas. Three or four, sanded between, gets you close to a glassy surface for fine detail.
On a rigid panel, a small foam roller gives a smoother result than any brush. Use a narrow one made for cabinet work rather than a wall roller, which leaves an orange-peel texture. Sand a very smooth panel lightly first so the primer has something to key into.
White, clear and black
White is the default, and the reason is optical. Paint applied over white reflects light back through the color, which is what makes it look luminous. Almost every color you put down will be brighter over white than over anything else.
Clear gesso adds tooth without hiding what is underneath. It is the one to reach for over a toned ground, a collage, or a printed surface you want to keep visible. It is also popular under pastel and colored pencil, because it gives a gritty surface that holds the pigment.
Black and colored gessos give a dark ground to work up from, which suits dramatic subjects and makes light colors sit on the surface rather than glow through it. Expect to need more coats of your lighter paints.
Common questions
Can I use gesso as white paint?
You can, and it will look chalky and matte and slightly absorbent, because it is formulated as a ground rather than a paint. It also has far less pigment than titanium white. Fine for blocking things out, poor for anything you want to stay looking that way.
Does gesso work under oil paint?
Acrylic gesso works under both oil and acrylic, and is what most oil painters use. The reverse of that rule is the one to remember: you cannot put acrylic on top of an oil-primed surface, because it will not bond.
Do I need gesso to paint alla prima?
The two are unrelated, though they get linked online. Alla prima means finishing a painting in one wet session rather than building it in layers, an approach in use since the fifteenth century and associated with Frans Hals, Velazquez, Sargent and the Impressionists. It says nothing about how the surface was prepared, and most painters working this way use a primed surface like everyone else.
The related name people are usually reaching for is wet-on-wet, the televised method taught by Bill Alexander and then by Bob Ross. That is a particular way of teaching alla prima quickly, not a different technique and not the origin of it.
How long before I can paint on it?
An hour is usually enough to recoat, but leave it overnight before painting, particularly if you intend to sand. Acrylic keeps hardening for days after it stops feeling wet.
My gesso dried with visible brush marks. Can I fix it?
Sand it back with fine paper once it is properly cured, then apply a thinner coat. Ridges nearly always mean the gesso was too thick or the coat too heavy.
What if I want to reuse an old painted canvas?
Two or three coats of gesso over the old painting will cover most of it, though heavy texture underneath will still show through as relief. Sand the worst of the ridges down first. It is a genuinely good way to get another canvas out of something that did not work.
If you would rather skip surface preparation altogether, every canvas in our paint by numbers range arrives pre-primed and printed, ready to paint the day it lands. The beginner's guide covers what to do with the first hour.
