Stretching your watercolor paper has certain aesthetic advantages. You'll end up with a perfectly flat surface on which to work. This surface will stay relatively flat as you work and the finished painting will dry perfectly flat. The only disadvantage is that it takes some effort and dedication to do it consistently. Any paper of less than #300 weight is bound to warp according to the amount of water absorbed in the painting process. Synthetic papers generally do not warp at all. Watercolor paper in prepared blocks will dry flat also, if left on the block to dry.
There are 4 ways to do it...
There are four traditional ways to stretch or mount your watercolor paper. You can use butcher's tape, staples, a frame and staples, or wheat paste. And there are always alternatives.
General Supplies
Water bucket, clean flat sponge, utility sponge, spray bottle, paper towels, scissors or mat knife. Staples, butcher's tape, or liquid gummed adhesive. Tempered masonite, sealed plywood, squared stretcher frame, Grafix Incredible Art Board or wooden drawing board.
Soaking your paper
This step is common to all stretching techniques. The easiest way is using your bathtub. Make sure it's clean and fill it about 6" deep with lukewarm water. Gently submerge your paper in the water in a sliding motion. After soaking about 5-10 minutes (depending on the weight of the paper) grasp a corner and pull the paper out of the water, supporting it while the water drips off. Lay the wet paper on a clean board and gently smooth the paper with a clean sponge and remove any excess water. Proceed to stretch the paper to your liking. You can also dampen the paper with a sponge and spray bottle on a clean board. You'll have to flip the paper a few times to adequately saturate the paper enough to stretch it.
Is it wet enough?
The usual rule is "Test the corners." If you bend a corner and it doesn't readily spring back, it's probably about right. If you meet resistance or it has too much "snap" it is not wet enough. If it's flopping around like a cooked lasagna noodle, it's way too wet to work with and you'll have to blot the heck out of it before stretching. Paper soaked too long can lose much of it's sizing and will affect the way it takes your paint.
Butcher's Tape method
"Butcher's tape" is made of heavy-weight kraft paper and has a water-soluable adhesive coating on one side. It is usually a kraft-paper-brown color and 3 to 4" wide. Your mounting board should be made of tempered (the darker stuff) masonite or a sealed plywood board at least 3/8" thick.The size should allow at least 4-6" of exposed board around the edges of your paper. Cut 4 strips of tape about 6" longer than your papers dimensions. Set them aside. Soak your paper taking care to blot the excess water from paper surface and edges. Using a utility sponge moisten the adhesive on the tape for the top edge of your paper. Align it with the top edge and let it overlap onto the paper at least an inch. Press, smooth and blot with sponge or paper towel. Repeat step 3 with left, right and bottom edges. Lay board FLAT while paper dries. Cut painting off board. Remove old tape as best you can, before stretching a new sheet.
What to avoid
Over-wet paper and/or over- or under- saturation of adhesive on the tape. Trying to rush drying with a hair dryer is risky at best.
Staple method
Use a 3/8" sealed plywood board, Grafix Incredible Art Board, or a traditional wood drawing board. A staple gun is a necessity! Soak your paper, position it on your board and blot the excess water from paper surface and edges. Starting from the left top edge put staples 1/2" in from outside edge and spaced about 1 1/2" apart aligned parallel with the paper edge. Repeat step 2 with left, right and bottom edges. Lay board FLAT while paper dries. Remove painting by removing staples. Use a staple-pulling tool. If you're in a hurry, cut the painting off the board. (But you'll have to remove those staples sooner or later, won't you?)
What to avoid
Busting your knuckles and hand cramps.
Wooden Stretcher method
For this method you'll use standard canvas stretcher bars and give your paper the fine linen treatment. There is a certain "giving" of the surface associated with working on paper stretched this way that is an aquired taste. It is much like painting on a stretched drum head. Do not tug paper taunt while stretching, just make sure it is flat. The shrinking of the paper as it dries will tighten everything up, so resist the urge to pull, excess tension can rip your paper as it dries. Start with a standard canvas stretcher that is sized to allow your paper to overlap about 2-3" on all sides. Square off frame and brace if necessary. Soak your paper taking care to blot the excess water from paper surface and edges. On a clean work area, overlap the top stretcher bar with the top edge (2-3") of the damp paper. Run a line of staples spaced between 1" to 1 1/2" down the top edge. Leave 2" unstapled paper on the corners for folding and stapling later. You may optionally fold the paper on to the back of the bar and staple there. Rotate piece clockwise, paper facing you, and staple the left edge in the same manner as step 5. At the corner you will do a standard "make-the-bed" fold-and-tuck before stapling down. Repeat steps with right and bottom edges. Lay stretched paper FLAT while drying. Cut painting from frame and remove staples.
What to avoid
Frustration if your first effort at frame stretching fails (rips or warps)
Wheat Paste method
For this method you use a mucilage (gum-based), wheat-based, or other starch-based water-soluable glue. This was the techique of choice before the advent of "butcher's tape" for packaging purposes. Position dry paper on mounting board. Mark edges with a pencil. Prepare wheat-paste or other glue, if necessary. Soak your paper, taking care to blot the excess water from paper surface and edges. Lay it out on a different, clean board. Using a clean utility brush apply liquid adhesive in a 3/4" strip around the inside edge of the pencil outline on your mounting board. Lay your blotted (no drips!) paper within your marked margins and smooth flat with a damp sponge. Lay board FLAT while paper dries. Cut painting off board. Remove old paper and glue residue as best you can, before stretching a new sheet.
What to avoid
The urge to eat paste and any consequences of sharp tools.
Alternatives and tips
You can stretch smaller, lighter-weight sheets with thumb tacks. You can use traditional tacks when stretching on stretcher bar frames. You can buy heavier weight paper. You can work in a smaller size. You can use #140 paper and masking tape or big metal clips and find the "natural warpage" of your materials organically endearing.
