Over time, paint often loses moisture and becomes too thick to use. While it can be tempting to throw thick paint away, this can be expensive. Knowing how to make paint thinner at home is not only quite simple, but can save you money and time. But before adding any homemade thinner, bring paint inside so it can warm to room temperature. Cold paint will be thicker than normal.
EditThinning Oil-Based Paint with Lemon and Linseed Oil
- Use lemon and linseed oil to thin paint. Measure out ¼ cup (59 ml) lemon oil and a cup (237 ml) linseed oil into a mixing bowl. Stir the ingredients lightly with a kitchen implement, like a spoon or fork.
- Thin paint with the lemon and linseed oil mixture. Add the mixture little by little to paint, stirring the paint with a paint stirrer as you do so. After adding about half a cup (118 ml) of the lemon/linseed mixture, allow the paint to rest.
- Allow the paint to rest for 3 to 5 minutes. Not allowing the paint time to bond with the thinner could result in you adding too much. Allow the paint to sit for roughly 3 to 5 minutes, then resume adding thinner until it reaches normal consistency.
- When the paint clings to your paint stirrer but still runs to its end to drip off, the paint’s been sufficiently stirred.
EditUsing Mineral Spirits or Acetone for Oil-Based Paint
- Acquire mineral spirits or acetone to thin the paint. Both of these common household products can be used to thin oil based paint. If you don’t have either, you can purchase both at your local hardware store or home center. 
- Put on a face mask, safety goggles, and rubber gloves. Although less intense than turpentine, mineral spirits and acetone both give off harmful fumes and are quite harsh. If you’re worried your clothes might be discolored by drops of thinner or paint, change into old clothes.
- Work in an area with good airflow. The fumes from mineral spirits and acetone, though moderate, can still be dangerous if they build up. For this reason, you should always thin paint like this in a well-ventilated location. Open doors and windows, if necessary.
- Rooms with poor airflow can be improved by putting a box fan in a window or door.
- Make sure the room’s clean before turning on the fan; you don’t want to blow dust into the paint.
- Pick out chunks of paint when thinning. When pouring your paint into the mixing bucket, you may find solid chunks in the paint. These are difficult to thin away. It may be easiest to pick these out by hand and throw them away as you find them.
- Pour mineral spirits and acetone into the paint in a 1:3 ratio. Generally, try to add 1 part of thinner for every 3 parts paint, or a 1:3 ratio. This means that for 3 gallons (11.4 L) of paint, you’ll add 1 gallon (3.7 L) of thinner. Pour half of the paint into a clean bucket, then add half the thinner. Add the remaining paint, then add the remaining thinner.
- Depending on how thick your paint is, the amount of thinner you will need to add may vary.
- The amount of thinner you use doesn’t have to be exact. Estimating the amount by eye should be good enough.
- Mix the thinned paint thoroughly. Use a paint stirrer to steadily stir the paint for several minutes. After that, stop stirring so the paint can rest. Now the paint’s ready to be stirred again. Add more thinner little by little, if needed, and stir the paint until it reaches ideal consistency.
- Most paints reach their ideal consistency when the paint sticks to the stirrer but still runs and drips off a little.
- Test the paint by applying it to a suitable surface. If the paint applies smoothly, it’s properly thinned and ready to be used.
EditUsing Water as a Thinner for Water Based Paints
- Use a large bucket to thin the paint in batches. Thinning paint in large batches will ensure more consistent quality. If your project will require a few buckets worth of paint, try to keep the consistency of each batch as close as possible.
- Transfer half of the total paint to the bucket. As you pour the paint into your bucket, pick out any solid chunks you see. For each gallon of paint in the bucket, add a half cup (118 ml) of room temperature water as well.
- Add the remaining paint and water to the bucket and stir. In the same proportions, a half cup of room temperature water for every gallon of paint, pour the rest of the paint into the bucket and follow it with the water. Stir the mixture thoroughly with a paint stirrer.
- Paint that sticks to the stirrer but still runs off the end in droplets should be well stirred.
- Ensure paint consistency with a viscosity cup. Submerge the cup in the paint, raise it above the can, and time how long it takes the cup to empty. All batches should take the same amount of time to drain.
- Viscosity cups can be purchased at most hardware stores, home centers, and paint stores.
- Tweak the consistency as necessary by adding small amounts of water. Some paint may only require a little more room temperature water added before it’s as good as new. Severely thickened paint may require a full cup or more.
- Take your time when adding water to the paint. You can always add more, but if you add too much, you may end up needing to thicken the paint.
- Use caution when adding thinner so you don’t add too much to the paint. Doing this could make it too thin and cause it to run.
- If you are concerned about your ability to successfully thin paint on your own, this service is usually offered at a hardware or home improvement stores. Be aware, however, that you will typically have to pay a small fee.
EditThings You’ll Need
- Lemon and linseed oil
- Mixing bowl
- Stirring implement (like a spoon)
- Paint stirrer
- Mineral spirits (or acetone)
- Breathing mask
- Safety goggles
- Rubber gloves
- Room temperature water
- Viscosity cup (optional)