This instructable is my effort to explain how to build your own custom size canvas' for painting. 16x20 and 18x24 common size are very affordable at most art supply stores but if you want large or custom sizes the price goes way up very quickly. All of the tools I used are common off the shelf things you can find at a home improvement store. 1x2" wood, nail gun(or use a hammer), miter saw(or you can buy a very cheap miter box), wood glue, T50 staple gun, and channel-lock pliers. All told once you have the tools you can build large scale stretched canvas' for $10.00or less.
For the wood frame you can buy 1x2 wood at most home improvement stores. You want to pay attention to the straightness in both direction of the wood you choose. 8 feet of it usually goes for about $1.50 so it's cheap. In this case I already had some scraps laying about so I like to reuse recycle where I can. I have two long pieces straight cut at 36" two shorter pieces straight cut down to 18" and then I took two more pieces and made 45 degree cuts in opposite directions on each end. These do not need to be a precise length as long as you make them the same.
besides a miter saw or a miter box these are the tools you need to assemble the frame. I have an air powered brad nail gun that has been a wonderful investment over the last few years but you could easily use a hammer and brad nails. Some wood glue.
Step 3: Building a Custom Stretched Canvas
Lay your frame out on a table long side in a vertical arrangement just like you see in the picture. Apply a little wood glue and clean up the access. Using the table and the wall as a backstop to hold the pieces together use your nail gun or hammer to put two brads in each joint. Continue around your frame until you have a rough box all nailed together. You will notice at this point the frame is still flimsy and will easily distort out of being square. The next step will fix this for you.
Just like earlier apply your glue to the ends. Hold your pieces with the 45 degree angles cut in each end into one corner. Nail in place Pick the exact opposite end and do the same with that corner. This makes sure the frame will remain square.
Now that you have a completed frame we need to stretch the canvas over it. You can find plain canvas at most fabric stores at a very reasonable price. I paid $7.00 for a square yard of it. When you measure out how much canvas you need allow for 3-4 inches on all sides so you can wrap it around the frame.
For this step you will need an average T50 stapler gun like you would find at any home improvement store. They are cheap and common. I begin with my longest sides first and I staple from the center out to the ends. Work from the center and staple every 1-2 inches until you are about 2 inches from the end leave that alone. I feel this helps decrease the chances of creases occurring. I staple one long side then turn it around to work on the other side.
I like to use a pair of channel lock pliers to grab the edge of the canvas and pull it around on the back end of the frame but I have done it without pliers also. They do make specialized pliers just for this purpose but I find it to be just as easy to use a $5.00 pair of channel locks in most instances. Again work from the center and staple every 1-2 inches until you are about 2 inches from the end leave that alone. Once you do your long sides like this you are going to do the same thing to the two shorter sides leaving the last 2 inches so that it is fairly tight and stretched all the way around except at the corners where the fabric will bow out. Don't worry if your canvas is not drum tight it doesn't need to be. Concentrate on making it wrinkle free is all.
This next part covers those corners and this is why I wanted you to leave a couple inches at each corner. Pinch your cloth tuck one side into the other like in the first picture then take the other side and square it along that corner, and staple in place. Some people get how to do this right away. Some people it takes a little bit of figuring it out. If you were in the military you might recognize this was how they had us make up our bunks in basic. This is not absolutely necessary, but it does make a neat clean look to your canvas.
This is what you end up with. A neat fairly wrinkle free canvas ready to be gessoed.
You now need to gesso your canvas. You can buy it at art supply stores in tubs for about $20.00 and it will last you many many canvas builds. Think of it as white acrylic paint. What it does is penetrate the canvas and makes a substrate you can paint on without worrying the paint you use will bleed and soak through the canvas material. Use a 3" brush. Any old brush will do. Start in the middle of your canvas and do as uniform strokes as best you can in a horizontal or vertical fashion. Wait for this coat to dry. You can even use a hair dryer to speed it up a bit. Then do another coat with strokes in the opposite direction. Make sure you also get around the sides of your frame. Wash your brush out put the lid back on your gesso and you are done. Take the canvas out in the sun to make sure it is a nice uniform application without bare spots you might have missed. If you did, add another coat. That's it you should be all done. Go paint your masterpiece.