I did a post on my floorcloths in the past, so I am not going to go through the entire explaination of what a floorcloth is, other than it is hand-painted canvas, that you can walk on...I suggest you go back into older posts, and read about the history, and see some examples (I have some at the end of this, as well), of what I have done.
My most recent floorcloth is a replica of an old, French Postcard.
So, you have your canvas. I know that some people, who make floorcloths, staple the canvas to a board or a tabletop. I used to do that, as it does shrink somewhat, but I no longer have a basement to work in - just a garage and no work table - I do miss my work table(very few basements in Texas), and it get's hot in the garage, but I make do. So, I went to Home Depot, and bought a large piece of mason board - it's about a quarter-inch thick, and is five ft. wide and about 7 feet long (or eight). I use it to roll my canvas out on after I have ironed it. I measure out the length...and then I cut it.
Determine what you want to be your finished size (I recommend starting smaller than wrestling with a large piece of canvas), and add two inches to each side...so it's your finished size & four inches on width and length.
While you are at Home Depot, go to the paint department...there's a "Whoops Pile" of paint, and I often pick up quarts of latex flat paint for a dollar...it's rejected because it wasn't the right color for the orginal customer. While there, pick up latex wall paint, flat, in a neutral color (get a gallon)...a roller tray (disposable liner), some fluffy, disposable rollers, and a long, detachable roller handle, so you are not doing this on your hands and knees. I also have a wide assortment of acrylic paints in my studio, so I have lots of choices when painting my floorcloth. You don't have to buy every color of paint in the world, just plan out what you want for your project, at first...It's gets expensive otherwise.
Ilay out my canvas, and roll paint on to it - going vertically, and then, horizontally. Let that dry, and do another coat. In order not to have my roller dry out, I put it in a large zip-lock freezer bag, and squish it up around my roller
I do two primer coats on one side, let that dry over night (I detach the long handle from the roller, put it in the zip lock bag, and then, put it in the refridgerator over night.)
Next day, flip it over, and do two coats on the other side...Told you this is labor-intensive.
I primed this piece of canvas with a neutral primer, and then, put my base coat on it. I usually do my base coat on both sides of the canvas, as sometimes, if I change my mind about what I want to do, or mess it up somehow, I can just flip it.
Okay, I blew it...the next photos will show you how to miter corners. I'm still learning that I have to post the photos backwards to get them to come out in the order I want...weird.
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Here is your mitered corner...I take a bit of double-stick tape, and put it inside the hem, close to the miter, just to hold it in place. Some people glue their hems down...I don't, as I have found it holds it's hem just fine, once you've turned it over, and gone over it again with a brayer.
Wet your sponge (tear it, so it has uneven edges) in water, squeeze out the excess, dip it in a dish containing acrylic paint (works better in this process than latex), and sponge it randomly onto the cloth- biggest mistake is to be too even...turn your wrist as you go...it's a bit scary at first.
Don't let it dry out...you need to work quickly..some people use glazing liquid, but then, it takes forever to dry for the next step. I often use a spray bottle of water to keep my surface wet.
Next, put another color on...I am using olive green and burnt sienna for this piece...Do the same thing...Then, spray a bit of water on the floorcloth, and go over it with a clean sponge..it will lift some of the paint, but that's fine.
Here is the piece once it was blended. I then market it off two inches all the way around (make sure your piece is totally dry, or it will lift the base coat), and put non-lifting painter's tape to mark your border (if you want a border)... Paint it, and then, lift the painter's tape pretty quickly after it's dried just a bit..otherwise it may life the border. If you have waited too long, and it's lifting the border, use a hairdryer on low heat on the tape, lifting as you go.
If you want, just do a stencil, or grid it, or just do a Jackson Pollock thing...don't let it scare you..
Practice makes perfect.
Once you have finished your floorcloth, you need to put at least three coats of non-yellowing, water-based polyurathane on it. Let it dry well between coats... Some people use wax on them after they polyurathane them..I don't.
It is important to put a non-skid pad (not waffle weave, as it will show through) under your floorcloth for safety.
Sheesh, I'm tired just writing about it...
Have fun with it, or just let me know, and I'll make one for you....!