How to stretch watercolour paper so it dries flat
In short: Soak the sheet in clean water (about 3 to 20 minutes depending on weight), lay it on a board, tape all four edges with dampened gummed tape, half on the paper and half on the board, and leave it flat overnight.
By Abu Bakar SaadatPublished 28 October 20264 min readPublisher: Saadat Rafiq
✓ Reviewed by Muqadas Fatima, BFA · 28 October 2026
IllustrationAt a glance
- You need
- Board, brown gummed paper tape, sponge, bath or tray, craft knife
- Soak
- About 3 to 20 minutes, by paper weight
- Tape
- Half on the paper, half on the board
- Dry
- Flat, overnight, no hairdryer
- Advice from
- Winsor & Newton, artsupplies.co.uk and TALAS, read 28 October 2026
- Checked
- October 2026
Watercolour paper ripples (cockles) when it gets wet because the fibres swell (TALAS), and paint then pools in the dips. Stretching soaks the sheet first and fixes it to a board while it is swollen; as it dries it shrinks tight and flat, and stays flat when you paint.
How long to soak, by paper weight
The three sources differ, so here are all of them. Shorter is safer: soaking too long can wash out the sizing, and paint then sinks into the paper (artsupplies.co.uk, TALAS).
| Paper weight | Winsor & Newton | artsupplies.co.uk | TALAS |
|---|---|---|---|
| 90lb (about 190gsm) | 4 to 5 minutes | 3 minutes | - |
| 140lb (about 300gsm) | - | 8 minutes | About 5 to 10 minutes |
| 300lb (about 640gsm) | 15 to 20 minutes | 20 minutes | - |
How to stretch the paper
Get the board ready and cut four strips of tape.
Illustration Cut four strips of brown gummed paper tape, a little longer than each edge, and keep them dry until you need them.
You should see: the board (sealed first, if it is MDF) and four dry strips of tape laid out within reach.
Careful: don't soak it longer than the table says. Too long can wash out the sizing (artsupplies.co.uk, TALAS).
Soak the sheet in clean water.
Illustration Put the sheet fully under clean water, with no detergent, in a bath, sink or tray (Winsor & Newton, artsupplies.co.uk). Don't crease it. Time it using the soaking table.
You should see: paper that feels floppy, like wet cloth. That's TALAS's test that it is ready.
Lay it on the board from the middle outwards.
Illustration Lift the sheet out by two corners and let the water drain off. Bow it slightly and lay it down from the middle so trapped air is pushed out to the edges (artsupplies.co.uk). Blot any pools of water.
You should see: the sheet lying flat on the board, with no air bubbles under it and no pools of water on top.
Careful: dampen the tape, don't soak it. Too much water washes the glue off (TALAS, artsupplies.co.uk).
Tape all four edges, half on the paper and half on the board.
Illustration Dampen each strip lightly with a squeezed-out sponge, just enough to make it sticky. Press it down so about half is on the paper and half on the board (TALAS), and smooth it without stretching the tape. Do all four sides.
Keep glue drips off the painting area: paint won't take there (artsupplies.co.uk).
You should see: a strip of tape along every edge, stuck flat with no loose corners.
Leave it to dry flat, ideally overnight.
Illustration Leave the board lying flat so water doesn't run to one edge, ideally overnight (artsupplies.co.uk, TALAS). Don't speed it up with a hairdryer; uneven drying can pull the tape loose (artsupplies.co.uk).
You should see: the dry sheet tight and flat, like a drum skin, and the tape stuck down all the way round.
Paint, then cut the finished painting free.
Illustration Paint while it is on the board. When the painting is completely dry, cut along the inner edge of the tape with a sharp craft knife (artsupplies.co.uk, TALAS).
You should see: a flat painting in your hand. The taped border stays behind on the board, or you can leave a strip on and hide it under a mount.
How to tell it worked
- The dry sheet is tight and flat, like a drum skin.
- The tape is stuck down all the way round, with no lifted edges.
- When you paint a wash, the paper stays flat instead of rippling (cockling).
- Paint takes evenly; dull patches can mean glue drips or lost sizing (artsupplies.co.uk, TALAS).
If it goes wrong
| What happens | What it means | What to do |
|---|---|---|
| The tape lifted and the paper rippled | Usually uneven drying, too much water on the tape, or a propped-up board (artsupplies.co.uk) | Soak again and re-tape with fresh strips |
| Bubbles under the paper | Air was trapped as you laid it down | Next time, lay it from the middle outwards as in Step 3 |
| Paint sinks in and looks dull | The sheet may have soaked too long and lost its sizing | Use a shorter time next time |
| No bath big enough | You can't soak the sheet in one go | Wet the sheet on the board with a sponge instead; it takes much longer (artsupplies.co.uk). Winsor & Newton says very big sheets can be soaked on the board for up to 25 minutes per side |
| You want to skip stretching | Some surfaces resist cockling | Heavier paper (300lb) resists cockling, and watercolour board stays flat even with heavy washes (TALAS) |
Questions readers ask
Do I need to stretch 300gsm (140lb) paper?
If you use a lot of water, yes. artsupplies.co.uk advises stretching anything under 425gsm (200lb) for wet work; TALAS says papers under 200lb cockle when wet. Heavier paper, or a watercolour block or board, can skip it.
Can I use masking tape instead of gummed tape?
Not for wet stretching. Masking and household tape don't stick to wet paper. Use brown gummed paper tape (gumstrip), which you dampen to activate.
Can I dry it faster with a hairdryer?
artsupplies.co.uk says not to: uneven drying can loosen the tape and cockle the surface. Leave it flat overnight.
How do I get the painting off the board?
When the painting is finished and dry, cut along the inner edge of the tape with a sharp craft knife. The taped border stays on the board, or can be hidden under a mount.
Sources
We base our articles on the makers' official documentation.
