Ever wondered how to stretch canvas or canvas prints and don't know where to start?
You've come to the right place. I've stretched hundreds (not exaggerating) possibly even thousands of canvases of my own and for other customers when I worked in a custom framing shop. It's one of the more simpler tasks for a custom framer and I'm happy to show you what I do and what works for me. Other people may have other methods, you have to find the one that works for you.
I'll talk you through the entire process, from measuring and cutting your own stretcher bars, to stapling the canvas into place and giving it a professional finish.
Tools & Equipment needed; blank canvas or canvas print, ruler, pencil, stretcher bars, chop saw, miter/corner clamps, wood glue, nail gun & nails, staple gun and upholstery staples, canvas pliers, canvas tape, drill or screwdriver, hangers & screws, and wire.
Step One: Measure for the Stretcher Bar Size
If you're stretching a blank canvas, you probably already have a size in mind, so you can skip to the next step!
If you already have stretcher bars assembled, you can skip to Step Four.
If you're stretching a canvas that is already painted, or a canvas print, you'll need to stick around for this part.
Lay your canvas flat out on a clear work surface.
I prefer to use a long ruler over a tape measure for accuracy and to avoid and 'slack' in the tape.
From the edge of the image, I come in about 1/8" and start my measurement, finishing an 1/8" in from the other end too. This is because I don't want any blank canvas creeping to the front.
So, for example, if my image is 30" x 19 1/2", my stretcher bar will be cut to 29 3/4" (30 - 1/8 - 1/8") x 19 1/4" (19 1/2 - 1/8 - 1/8").
In the photos below, I have already moved my ruler in 1/8" and will come in 1/8" from the other edge, so my stretcher bar for this length needs to be cut to 24 3/16" (24 7/16 - 2/16 - 2/16")
Make a note of this measurement and measure the other side. It's important to take as accurate measurements as possible.
Step Two: Cut the Stretcher Bar
Stretcher bars look like cheap wood, and indeed, they mostly are compared to other frame mouldings, but they have a crucial difference from the 1x2" at your local hardware store. They have a rounded lip on them, pictures below, and have been kiln dried to prevent warping. The important lip prevents wear and tear on the canvas as wood and fabric expand and contract with changes in temperature and humidity throughout the year.
I recommend picking up lengths from your local framing shop.
Cut one end of your stretcher bar length at a 45° angle; the lip should be face up and flush to the back of the saw. It'll end up on the front of the stretcher bar and the outer edge.
From the cut, measure out one of your lengths and make a mark.
Flip your saw around so that the 45° angle is the other way and chop at the mark you made. The lip should be on the longest side of the stretcher bar. See pictures below.
Repeat for all 4 lengths to make a frame.
Check that your matching lengths are the exact same size to each other, so you don't get a trapezoid effect frame.
Step Three: Glue the Stretcher Bar
Take one of your longest lengths and one of the shortest lengths of stretcher bar you just cut.
With the lip of the bar face up, glue them together in the miter/corner clamp, squeezing for a very tight and secure fit.
Make sure the lengths are positioned so they form a nice 'corner'.
The corner should be flush in all directions; adjust if part is sticking ahead, up or down. See examples of 'good' and 'bad' corners below.
Repeat for the other long and short bars, leave to dry for a minimum of 20 minutes.
Once the glue is dry, you should have 2 identical L shaped bars, (corners 1 & 2 pictured below).
You can glue corners 3 & 4 at the same time IF you have 2 mitre clamps that are perfectly level to each other, and I mean PERFECT! if they're not, you're setting yourself up for all kinds of problems.
At this point, I position myself at eye level to the clamp to make sure my bars aren't gluing away from each other in a weird direction and adjust accordingly. This is how you can make sure your canvas will sit flush against the wall without a corner sticking up.
Once dry, nail each corner with a nail gun to prevent the bars from coming apart at later date.
For Larger Canvases; Add a Cross Bar/Support Bar
For larger canvases I like to add a support bar to prevent the stretcher bar from bowing in under the tension from the stretched canvas.
Measure the distance between the inside of the bars so you know how long the support bar should be. Measure at one end for accuracy, we know that length is correct. If you measure in the middle and your bars have a slight bow in or out, you won't know. By measuring the end, you can correct any flaws in the stretcher bar.
Cut your cross bar; a piece of 1x2 is fine for this.
Measure to find the centre of your stretcher bar length.
Glue the cross bar into place, secure with clamps if necessary for a tight fit. Make sure it isn't protruding in front of the lip of the frame, otherwise your stretched canvas will rub against it.