To flatten watercolor paper after painting, I let the painting dry completely, lightly dampen the back of the paper, place it between clean sheets, and press it evenly between two flat boards until it dries. The important part is introducing very little moisture and keeping water away from the painted surface.
I’ve had plenty of watercolor paintings dry with waves or curled edges, especially after using larger washes. A little movement doesn’t bother me in a sketchbook, but I want the paper much flatter when I’m preparing a painting for scanning, framing, or storage.
Below is the method I use for flattening finished watercolor paintings, along with a few things I avoid because they can put the paint or paper at risk.
How to Flatten Watercolor Paper After Painting
- Let the painting dry completely.
- Turn the painting face down on a clean surface.
- Lightly dampen the back of the paper.
- Place the painting between clean protective sheets.
- Sandwich everything between two smooth, flat boards.
- Add even weight and leave it until completely dry.
For a painting I care about, I don’t rush this process. I’d rather use too little moisture and repeat the pressing process than saturate the sheet and risk disturbing the artwork.
Step 1: Let the Watercolor Painting Dry Completely
I don’t try to flatten a painting immediately after finishing it.
The paper may look dry while still containing moisture, particularly after heavy washes. I want the painting fully dry before I begin handling and pressing it.
For me, that usually means leaving it alone overnight or longer rather than trying to flatten it the same day.
If the sheet is taped to a board, I also remove the tape slowly instead of pulling it sharply away from the surface.
If tape itself is causing problems, see my guide to the best tape for watercolor paper.
Step 2: Lightly Dampen the Back of the Paper
I place the painting face down so I’m working only on the unpainted back.
Then I introduce a small, even amount of clean water to the back. A fine mist can work well because I can add moisture gradually rather than soaking one area.
My goal isn’t to saturate the sheet. I only want to relax the paper enough that it can settle flatter while it is pressed.
The paper should become slightly pliable rather than wet enough to form puddles.
Why I Don’t Wet the Painted Side
I avoid deliberately misting the front of a finished watercolor painting.
Watercolor remains sensitive to water after it dries. Adding moisture directly to the painted surface can disturb washes, edges, lifted areas, or other details I want to preserve.
Working from the back lets me introduce some moisture into the paper without intentionally re-wetting the painting itself.
Step 3: Put the Painting Between Clean Sheets
Once the back is slightly damp, I place the painting between clean, smooth protective sheets.
I don’t want a textured surface pressed directly against the artwork because texture can potentially transfer into damp paper.
The setup is essentially:
- Flat board
- Clean protective sheet
- Watercolor painting
- Clean protective sheet
- Flat board
Everything touching the painting should be clean, smooth, and free from ink, texture, paint, or debris.
Step 4: Press the Painting With Even Weight
I place a second flat board over the painting and distribute weight evenly across it.
Heavy books can work as the weight, but I spread them across the surface rather than putting one heavy object in the center.
The objective is even pressure across the entire sheet while the slight moisture introduced from the back disappears.
How Long Should You Press Watercolor Paper?
I normally leave the painting pressed for about 24 hours before checking it.
A stubborn sheet may need longer. If it still has noticeable waves, I would rather repeat a gentle flattening process than compensate by making the paper excessively wet the first time.
I don’t remove the painting from pressure while the paper still feels damp.
Can You Flatten Watercolor Paper Without Water?
If the curl or buckle is minor, I try dry pressing first.
I place the completely dry painting between clean sheets and leave it beneath even weight. This is the least invasive option because I’m not reintroducing moisture.
For a more stubborn warp, a very small amount of moisture on the back can help relax the paper before pressing.
Can You Iron a Watercolor Painting Flat?
I don’t use an iron directly on a watercolor painting.
Direct heat introduces another variable that I don’t need, especially when I’m dealing with a finished piece. Steam is even less appealing because it combines heat with moisture near the painted surface.
For my work, gradual moisture from the back followed by cool, even pressure is a much more controlled approach.
How to Flatten Warped Watercolor Paper
The more severe the buckle, the more tempted I am to add extra water or weight. I try not to.
For badly warped watercolor paper, I use the same process but work gradually:
- Start with the painting completely dry.
- Dampen the reverse side evenly rather than soaking isolated areas.
- Press the whole sheet between smooth surfaces.
- Allow it to dry fully under pressure.
- Repeat gently if necessary instead of dramatically increasing the moisture.
If a painting is valuable, irreplaceable, or made with materials I’m uncertain about, I would be more conservative and consider professional framing or paper-conservation advice rather than experimenting aggressively with the finished artwork.
Why Watercolor Paper Buckles
Water changes the dimensions of paper fibers. When one area becomes wetter than another, the sheet expands unevenly and develops waves or buckles.
How much movement I see depends on several things:
- The weight of the paper
- How much water I’m using
- Whether the sheet is secured
- The size of the painting
- How evenly the sheet becomes wet
My guide to watercolor paper types explains the differences in surface, fiber, and weight in more detail.
How to Prevent Watercolor Paper From Warping
Flattening solves the problem afterward. Preventing excessive buckling while I’m painting is a separate problem.
The main things I consider are:
- Using watercolor paper appropriate for the amount of water in the technique
- Securing loose sheets before painting
- Stretching paper when I’m planning particularly wet work
- Controlling unnecessary pools of water
If prevention is what you’re trying to solve, use my dedicated guide to how to stop watercolor paper from buckling. I keep that separate from this page because preventing buckling and flattening an already finished painting are different tasks.
Does Heavier Watercolor Paper Stay Flatter?
Heavier paper generally moves less dramatically under normal watercolor use than a very lightweight sheet, although I don’t assume any paper will remain perfectly flat under every amount of water.
I commonly work with 140 lb / 300 gsm watercolor paper, while heavier paper can be useful when I know I’ll be working very wet.
If you’re trying to choose between weights rather than repair an existing painting, see my types of watercolor paper guide.
Can You Flatten a Watercolor Sketchbook Page?
Bound sketchbook pages require more caution because I can’t simply sandwich an individual sheet between two boards.
For mild curling, I first try closing the completely dry sketchbook and placing even weight over the cover.
If I decide additional flattening is necessary, I protect the painted page from the facing page and use as little moisture as possible. I don’t want trapped moisture remaining inside a closed book.
If sketchbook paper frequently buckles because of the way you paint, it may be worth choosing a book with heavier or more suitable watercolor paper. My watercolor sketchbook guide covers what I look for.
What I Avoid When Flattening Watercolor Paintings
- Soaking the finished painting. I use as little moisture as I can.
- Spraying the front. I don’t deliberately re-wet the painted surface.
- Direct ironing. I avoid putting concentrated heat onto finished watercolor.
- Steam. I don’t want uncontrolled heat and moisture around the painting.
- Pressing a painting that is still wet from the painting process.
- Pressing against a textured or dirty surface.
- Using uneven weight. I want pressure distributed across the whole sheet.
Flattening vs. Stretching Watercolor Paper
These are two different processes.
Flattening is something I do after a finished sheet has already warped.
Stretching is preparation done before painting to help the sheet remain more stable when water is added.
If you’re preparing a fresh sheet rather than fixing a finished painting, see my guide on how to stretch watercolor paper.
Flatten the Painting Slowly
The biggest thing I’ve learned is not to turn flattening into another aggressive process.
I let the painting dry, work from the back, introduce moisture gradually, and use even pressure while the sheet dries again.
That takes longer than trying to force the paper flat immediately, but I’m much more comfortable being patient with a finished watercolor than risking the painting to save a few hours.