Every watercolour artist knows that wet paper, even of 300 gsm or more, will warp and cockle when you paint. I have tried a lot of different methods to tape down my paper, but every sort of tape I’ve ever used ended up being a nuisance, so most of the time, I painted on untaped paper. When I started painting very wet, around 2016, that wasn’t enough anymore, so I looked for solutions. I found a mention of watercolour paper stretchers and went looking – and I’ve never used anything else since.
My watercolour stretchers are from Brown Tree Art, UK. I’ve got them in three different sizes (A4, A3 and one in between). Which is a bit if a luxury, I suppose . ;)
They consist of a solid wooden panel with one slim wooden flap on every side. The flaps are quite loosely attached to the panel with sturdy fabric tape, and can fold back all the way; they hold your paper in place. They’re probably not hard to build, but I’m rotten with any sort of craft that involves something other than paper, so I just bought mine.
It’s important to soak the paper thoroughly before stretching it. I put my sheet in a cheap plastic tray in the sink and let it sit immersed for about two minutes. By that time, the paper fibres have taken up enough water to expand to their fullest extent (and you’ll notice that your paper is indeed a bit larger now than what you started out with). Don’t let it soak much beyond that, or it’ll tear.
You then tilt back the battens on each side, lay the wet paper into the stretcher, and then fold them back in where they’ll hold your paper in place. The paper will lie quite flat all on its own, but you can smooth it down with a bit of tissue to be sure.
Once the paper is snugly fixated by the flaps, clamp everything into place with paper clips. It’s important to put the first clips where the flaps meet, but especially when I’m working larger, I like to fixate the long sides as well. Plus, I have too many clamps and they need to go somewhere!
The paper then dries, and stretches itself.
When you start working, and use a lot of water, your paper will still form little warps and puddles (visible in the very bottom here), but they’ll always dry and stretch again to be completely flat. When your painting is done, wait until it’s completely dry before removing it from the stretcher. It’ll be completely flat and ready to be matted and framed.