There are two effective ways to stretch your watercolour paper; stretching on a flat board and stretching on a purpose-made frame.
Stretching on a flat board
Using a board is the most common way of stretching paper. Spruce drawing boards (draughtsmen’s boards) are the best option because they are hard-wearing and durable. However, they are not easy to find. MDF board can also be used but it should be sealed beforehand so that water doesn’t penetrate. For paper under 24in square a 12mm board thickness is suitable; for larger sheets, increase the thickness of the board to prevent warping. A thicker board is best because you can use both sides. Alternatively, you can brace the 12mm board on a frame.
Allow 1in for gummed paper tape all the way round your paper when cutting to size. Fill a large sink or bath with water and submerge the paper, rolling or folding it as necessary, but avoiding creasing it. A heavy paper (300lb/640gsm) must soak for 15 to 20 minutes, while a lightweight one (90lb/190gsm) needs only four to five minutes.
If the paper is too large to submerge it can be soaked on the board, but allow up to 25 minutes soaking on each side to ensure expansion of the paper.
After soaking, remove the paper and allow the excess water to drip off before lying it on the clean board. Using traditional gummed paper strip, tape down the edges and leave the board to dry flat. Both sides of the board can be used – simply stand the board on four ink bottles to let the air circulate.
Stretching on a purpose-made frame
It’s possible to purchase stretching boards or ‘paper stretchers’ from your local art store.