Quick answer: How to thin acrylic paint depends on what you are using it for. For everyday brushwork, add small amounts of water a few drops at a time. For glazes, washes over non-absorbent surfaces, pouring or airbrushing, thin with an acrylic medium (glazing, flow, pouring or airbrush medium) instead of large amounts of water, because mediums add binder and keep the paint film strong. Always mix with a palette knife and test on scrap before committing.
There is no single right consistency for acrylic paint. A glaze needs to be as thin as tinted water, a pour needs to move like warm honey, and an airbrush needs paint closer to whole milk. Thinning well means picking the right thinner for the job and stopping at the right consistency.
This guide covers how to thin acrylic paint for art, craft and hobby uses, with a thinner comparison table, target consistencies, and specific methods for glazing, pouring, airbrushing, miniatures, paint by numbers, craft paint and metallic paint.
What to Use to Thin Acrylic Paint
| Thinner | What it does | Best for | Limitations |
|---|---|---|---|
| Water | Reduces thickness quickly | Small adjustments, washes on absorbent paper | Large amounts dilute binder; may weaken adhesion and look chalky |
| Gloss or matte medium | Thins while adding binder; sets sheen | Glazes, transparent layers | Changes finish depending on gloss or matte |
| Glazing medium | Thin, transparent layers with a little extra open time | Glazing, color shifting | Can lengthen drying time slightly |
| Flow improver (flow aid) | Reduces surface tension so paint levels and flows | Smooth flat areas, line work, washes | Use in small amounts; too much can cause problems |
| Pouring medium | Makes paint fluid while keeping a strong film | Acrylic pouring | Long drying times for thick pours |
| Airbrush medium or thinner | Thins to spray consistency while maintaining binder | Airbrushing, spraying | Product-specific; follow label |
| Manufacturer’s own thinner | Formulated for a specific paint line | Hobby and model acrylics | Often brand-specific |
Paint type sets your starting point. Heavy-body paint needs much more thinning than fluid or high-flow paint, which is already close to working consistency. If you regularly need thin paint, choosing a fluid formula saves time; see our breakdown of the best acrylic paint brands by body and consistency for options.
Can You Thin Acrylic Paint With Water?
Yes, and for many everyday tasks water is fine. The issue is quantity. Acrylic paint holds together because of its acrylic binder. Water adds no binder; it only spreads the existing binder thinner. A small amount is harmless, but heavy dilution can leave too little binder to hold pigment firmly, especially on non-absorbent surfaces like primed canvas, plastic or glass.
Signs you have added too much water include paint that beads up, looks blotchy or chalky when dry, rubs off easily, or lifts when you paint the next layer. When you need very thin paint on non-absorbent surfaces, a medium is the safer choice. On absorbent surfaces like watercolor paper, thinned acrylic soaks in and is generally more forgiving.
Target Consistencies by Use
| Purpose | Target consistency | Typical thinner |
|---|---|---|
| General brushwork | Soft butter to thick cream | A little water or none |
| Smooth flat coverage | Heavy cream | Water with a touch of flow improver |
| Glazing | Transparent, like tinted syrup | Gloss or glazing medium |
| Washes on paper | Like ink or tea | Water (absorbent surface) |
| Pouring | Warm honey | Pouring medium |
| Airbrushing | Whole milk or thinner | Airbrush medium or thinner |
| Miniature basecoats | Skim milk to light cream | Water or a dedicated medium |
How to Thin Acrylic Paint for Art: Basic Method
- Put the paint on the palette. Squeeze out the amount you need.
- Add thinner next to the paint, not directly on top, starting with a small amount (a few drops of water or a little medium).
- Mix with a palette knife, pulling the thinner into the paint until uniform. Brushes can leave unmixed streaks and wear out faster.
- Check consistency by lifting the knife and watching how the paint drops or flows.
- Add more gradually until you reach the target.
- Test on scrap of the same surface and let it dry before using it on your painting.
How to Thin Acrylic Paint for Glazing
Mix a small amount of paint into a larger quantity of gloss or glazing medium. Start with roughly one part paint to several parts medium and adjust for the transparency you want. Brush the glaze thinly over a completely dry layer. Multiple thin glazes build depth more smoothly than one heavy one. Transparent pigments, such as quinacridones and phthalos, make the clearest glazes.
How to Thin Acrylic Paint for Washes and Underpaintings
Many painters start a canvas with a thin, transparent wash to tone the white surface or sketch the composition. Mix a small amount of a neutral color, such as burnt sienna or a warm gray, with water or a matte medium until it looks like strong tea. Brush it across the canvas and wipe back lighter areas with a paper towel. Because the layer is so thin, it dries in minutes and gives you a mid-tone ground that makes judging values easier.
On watercolor paper, acrylic washes can be thinned mostly with water, since the paper absorbs the paint and holds the pigment. Unlike watercolor, the dried wash will not lift when you paint over it, which lets you layer freely.
Thinning for Different Surfaces
| Surface | Absorbency | Thinning approach |
|---|---|---|
| Watercolor or mixed-media paper | High | Water is generally fine, even for very thin washes |
| Primed canvas or panel | Low to medium | Small amounts of water; medium for glazes and thin layers |
| Raw wood | High and uneven | Seal or prime first, then thin as for canvas |
| Plastic, glass, metal | None | Avoid heavy water dilution; use medium and a suitable primer |
| Fabric | High | Mix with textile medium rather than water |
How to Thin Acrylic Paint for Pouring
- Pour your paint into a cup and add pouring medium. Many pourers start around one part paint to one or two parts medium, adjusting for how thick the paint is.
- Stir slowly and thoroughly to avoid creating bubbles.
- Add a few drops of water if needed to reach a warm-honey consistency. A good test: lift the stirring stick; the paint should flow off in a steady stream and the trail should sink back into the surface within a second or two.
- Let the mixed paint rest for a few minutes so bubbles rise and pop.
- Match all colors to the same consistency so they flow evenly together.
How to Thin Acrylic Paint for Airbrushing and Spraying
Airbrushes need paint thin enough to atomize without clogging, but with enough binder to adhere.
- Start with fluid or high-flow acrylic if possible; heavy-body paint needs a lot of thinning and may contain coarser pigment particles.
- Add airbrush medium or thinner gradually, aiming for a milk-like consistency.
- Strain the mix through a fine mesh or paint strainer to remove lumps.
- Test spray on scrap at your normal pressure. Adjust thinning if the paint spatters (too thick) or runs (too thin).
- Flush the airbrush with water or airbrush cleaner frequently to prevent paint drying in the nozzle.
Fluid acrylics are often chosen as a starting point for airbrushing because they need less thinning. Our Daler-Rowney fluid acrylic review covers how one fluid formula handles thin applications.
How to Thin Acrylic Paint for Miniatures
Miniature painters often talk about “two thin coats” rather than one thick coat. Thin paint preserves fine sculpted details that thick paint can fill in.
- Use a wet palette to keep small amounts of paint at a consistent thinness.
- Thin with water or a dedicated medium to a skim-milk to light-cream consistency.
- Test on the back of your hand or a plastic sprue: the paint should flow smoothly without pooling in recesses or leaving a tide line.
- Apply multiple thin coats, letting each dry.
Hobby acrylics
Some hobby and model acrylic lines, such as those used for scale models, are formulated differently from artist acrylics and are often alcohol-based. Many of these brands sell a dedicated thinner, and the manufacturer’s own product is usually the safest choice. Test any alternative on scrap first.
How to Thin Acrylic Paint for Paint by Numbers
Paint-by-number pots sometimes thicken over time or arrive thicker than expected. Add a drop or two of water to the pot, stir thoroughly with a toothpick and test on the edge of the canvas. Thin only what you need; overly thin paint may not cover the printed numbers and lines. Two thin coats usually cover better than one heavy one.
How to Thin Acrylic Craft Paint
Craft paint is usually thinner than artist paint already and contains less pigment. Add water sparingly, a few drops at a time, or use a flow medium for smooth coverage on wood and other crafts. Over-thinned craft paint can turn streaky and translucent, needing many coats.
How to Thin Metallic Acrylic Paint
Metallic paints contain mica or similar reflective particles. Heavy dilution with water can spread those particles too thinly and reduce shimmer, leaving a patchy look. Thin with a gloss medium or flow improver instead to keep particles suspended and the finish bright. Stir thoroughly, since metallic particles can settle.
How to Fix Acrylic Paint That Is Too Thick
If paint in a tube or jar has thickened, add a few drops of water or flow medium, stir well and let it sit for a few minutes before stirring again. If the paint has become rubbery or formed lumps, it has partially dried and cannot be restored; strain out the lumps or replace the paint.
Storing Thinned Paint
Thinned paint is useful to keep on hand, especially pouring mixes and airbrush colors. Store it in airtight containers such as small squeeze bottles or jars with tight lids, and label each with the color and ratio you used. Shake or stir before each use, because pigment can settle. Mixes thinned with plenty of water may develop mold or an off smell over time, so make smaller batches if you paint infrequently.
Common Thinning Mistakes
- Adding a lot of water at once. Easy to overshoot; add gradually.
- Mixing with a brush. Leads to streaks of unmixed thinner and wears out brushes.
- Skipping the test. Paint looks different wet and dry, and different on each surface.
- Using water for glazes on canvas. A medium gives stronger, clearer glazes.
- Inconsistent pouring paint. Colors of different consistencies do not flow together well.
- Thinning metallic paint with water. Can dull the shimmer.
FAQs
What is the best way to thin acrylic paint?
For small adjustments, water works well. For glazes, pouring, airbrushing and very thin layers on non-absorbent surfaces, an acrylic medium is better because it adds binder and keeps the paint film strong.
How much water can you add to acrylic paint?
Guidance varies by manufacturer and surface. Small additions are generally safe; heavy dilution on non-absorbent surfaces can weaken adhesion. If you need very thin paint, switch to a medium rather than adding more water.
Can I thin acrylic paint with rubbing alcohol?
Some hobby painters use small amounts with certain alcohol-based hobby paints, but alcohol can cause standard artist acrylics to gum up or dry too quickly. For artist acrylics, water or an acrylic medium is the safer choice.
How do you thin acrylic paint for an airbrush?
Use fluid or high-flow acrylic, thin it with airbrush medium or thinner to a milk-like consistency, strain it and test spray on scrap before use.
How do you thin acrylic paint for pouring?
Mix paint with a pouring medium, add a little water if needed, and aim for a warm-honey consistency that flows off a stick in a steady stream.
Does thinning acrylic paint change the color?
Thinning increases transparency, so colors look lighter over a light surface and less opaque. With a gloss medium, colors may appear richer; with matte medium, slightly lighter.
Final Thoughts
Thinning acrylic paint well comes down to two choices: the right thinner for the job and the right target consistency. Use water for small tweaks, mediums for glazes, pours and airbrushing, and a palette knife and a test strip every time.
Starting with a paint whose body suits your style reduces how much thinning you need. To compare heavy-body, soft-body and fluid options side by side, see our guide to acrylic paints for every consistency and technique.
