& CANADA 
How do you stretch a canvas? Watch as Bob Nadon of Upper Canada Stretchers shares tips and best practices for stretching cotton or linen canvas on a stretcher frame. Step-by-step instructions are also pictured below.
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1. On a flat surface, lay your assembled stretcher frame canvas-side down on the canvas. (See here for assistance on assembling a stretcher frame and how to check for squareness). Be sure to leave just enough canvas on all sides to cover the depth of the stretcher frame and an additional 2" or so to pull around the back.
2. Start by stapling the canvas in the centre of each bar, moving to the opposite side each time (note order in the photo of #1, #2, #3, #4). Pull canvas tight using canvas pliers or by hand and staple in place. Add at least 3 staples in each location to start (about 1-1.5" apart), so the canvas does not tear around the staples.
3. Always alternating across the four sides (locations #1-4), drive 3 more staples on each side of the initial staples, applying tension to the canvas while stapling.
4. Continue in this fashion, working from the centre out, adding 3-5 staples at a time.
5. Staple all the way to the ends of the side bars but leave about 6 inches unstapled at each end of the bottom and top bars to allow for the corner folds. (This is so that the sides, which are most visible when the canvas is hung, are left smooth.)
6. Grabbing the corner of the loose canvas, pull it in on a 45 degree angle, making sure that the canvas underneath is folded to lay smooth.
7. Staple the triangular area now lying flat against the stretcher bars.
8. Pull the remaining canvas in tight and staple, again making sure the underlying canvas lays smooth.
9. This is what a finished corner looks like. Repeat on the remaining corners.
10. To add keys (note Caution below), insert them in both corner slots, along with those on any braces, and tap in firmly with a hammer to expand each joint equally to provide the desired tension to the canvas.
CAUTION WHEN WORKING WITH RAW CANVAS: When gesso is applied to raw canvas, very high tension forces can develop due to the shrinkage of the wet canvas, especially on large canvases and when linen was used. To avoid excessively high strain and potential warping of the frame, do not add the keys until AFTER the canvas has been sized and/or primed (and has thoroughly dried). Applying gesso will tighten the canvas on its own and provide you with a firmly stretched canvas base for your painting – the keys can expand the frame further afterward if any slack remains after priming.
How do I choose the right stretcher bars?