You can stretch a painting that has been painted on unstretched canvas. I have never had a painting crack from delayed stretching, but it is probably best to do the stretching within a month of the painting process. Once the paint has dried in, cracking is a possibility.
To stretch a prepainted canvas, you need a stretcher bar of the proper size, canvas pliers, a staple gun, 4 push pins, and a tape measure.
|1. Check that your stretcher is square.|
|2. Locate corners of painting.|
2. Locate the corners of your painting by pinching them between your thumb and forefinger.
|3. Place corners of painting on corners of stretcher.|
3. Place the corners of the painting on the corners of your squared stretcher. You can feel the corners with your forefingers, or press down slightly on the canvas so that the edges of the stretcher appear as rises in the canvas.
|4. Pin in place.|
4. Pin the canvas temporarily in place with the pushpins, one in the center of each side. You should be able to tell if the canvas is square on the stretcher at this point. If it isn't, go back and repeat steps 2 and 3.
|5. Staple the middle of the first side.|
5. Staple the middle of the first side. You can see the push pin here, holding the canvas in place.
|6. Use canvas pliers to stretch other sides before stapling.|
|7. Once centers of all sides are stapled,|
check on the front to be sure canvas is located well.
|8. Choose which dimension will have corner fold bulk.|
|9. Staple sides from center outward.|
9. Once you have decided which way you will fold the corner, stretch and staple the sides of the canvas, moving from the center toward the corner. On the sides that will be smooth, staple all the way to the end. On the sides that will have the corner fold bulk, stop about 2 inches from the corner to leave space for folding. Once all four sides are stapled, check again to see that your canvas is still square on the stretcher. At this point the canvas should be drum taut, and make a nice little boing sound when you tap it.
|10. Stretch corner around to bulk-of-fold side.|
|11. There is an extra flap of canvas, see?|
|12. Crease this flap along the diagonal where it is bulky.|
|13. Fold the flap down across that crease.|
13. Now fold the flap of fabric down across that crease, toward the back of the canvas. This should enable the bulky side to smooth out, mostly. There will be a little bump (just above my thumb in the illustration) where the bulk is folded underneath.
|14. On the back, tuck the smooth side underneath the flap.|
14. Set the canvas down. On the back, tuck the smooth side of the canvas under the flap, right up to the edge of the stretcher. At this point you have a sort of double flap on the back of the canvas,with the inner part slightly smaller than the outer part. You can see this double flap raised over my thumb.
|15. Pull the flap down tightly and staple.|
Photos by Richard Gardiner
15. Pull the whole double flap down against the back of the stretcher bar. Pull hardest on the outside flap, and it will cover the little inner one. You can stretch it with the canvas pliers, or not. Then staple it down. Do the same process with the other corners, and you are done!