Paint spray guns can be a great tool in making your painting project a breeze.
Why go through the tedious process of hand painting a large surface with a small brush when you could be coating the entire walls in just minutes with a spray gun?
Before you get too trigger-happy, though, there are some things you need to keep in mind.
For example, if you use oil-based paint in your spraying gun, you need to thin it out before it can be used.
How exactly do you do that? Is it easy? Do you need special equipment? And why should you use oil-based paint as opposed to latex?
I will answer all of these questions and more here in this article. So, get your drop sheets ready because we are about to get started.
What is Oil-Based Paint?
There are two primary types of paint—latex and oil.
Latex paints are water-based, thicker, and tend to dry quickly, while oil-based paints are thinner and stay wet longer.
Now, latex paints have their place and benefits, but because oil paints tend to be thinner at the start and don’t clog up the gun by drying in the nozzle, they are more commonly used in spray guns.
When it comes to oil paints, there are then two subtypes—synthetic and natural.
Synthetic oil paint is usually referred to as alkyd, whereas natural oil paints are called linseed. As with most things, the natural option tends to be more expensive.
Regardless of the type you are using, oil-based paints are a complex combination of oils, chemicals, and solvents; and sometimes, the mixture can be too thick for spray guns and need to be thinned out.
Things You Will Need for Thinning Oil-Based Paints
The first step begins at the paint store. While you are at the store, you’ll need to purchase some thinning agents.
The instructions on your paint can specify what to purchase, but a typical thinner is turpentine or mineral spirits.
Alternatives such as acetone, alcohol, or kerosene can also be used in case you do not have paint thinners available.
But remember, these may not bring the finish you want from the paint job.
When buying thinner oil-based paints, remember that paint thinner solvents for latex paints differ from those used for enamel and oil paints.
So, make sure you buy the appropriate paint thinner that can be used for oil paint in your spray gun.
It will also help to have the painting tools, such as buckets that you are OK with being painted permanently, some stirring sticks, paint strainers, gloves, and a funnel.
When buying oil-based paint for spraying, also be aware that not all paints can be thinned.
So when shopping around, check the label to make sure you are purchasing an oil-based paint that can either be used directly in the spray gun you have or can be thinned for spray gun use.
The type of spray gun you use matters a lot. Some paints and guns are incompatible even after the paint has been thinned.
So, don’t be afraid to talk to a paint expert at the store to make sure you are using a good paint/spray gun combination.
How to Thin Oil-Based Paints for Spray Gun? (5 Easy Steps)
Once you have made the correct purchases, check the paint label for thinning instructions.
In most cases, thinning your oil-based paints for an HVLP spray gun can be done as follows…
Step 1- Get the paint ready
First, pour the paint into the bucket through the strainer, which will catch any paint clumps.
If you do not have a strainer, simply search through the paint (while using a stirring stick to stir the paint) and throw out any hard chunks that might be floating on top.
Step 2- Add thinner
Next, you need to add the thinning agent.
Follow the paint-to-thinner ratio for the airless spray gun specified on your paint label.
A good rule of thumb is 1 part thinner (mineral spirits or turpentine) for 3 parts of oil-based paint you need to thin.
Make sure that you do not add thinner more than this, or else the shade you get on the finished surface will be lighter than what is desired.
Also, it’s essential to keep the amount of oil paint higher than the thinner so that you do not turn the paint watery, which can cause problems.
Step 3- Stir
Once you have added the solvent, stir the thinner into the paint thoroughly using a clean stir stick made of wood or plastic.
A paint stirrer that attaches to your drill can also be used, and it will work faster if you have a good amount of oil-based paint to mix.
Step 4- Check
A good way to ensure the oil paint is thin enough for spraying in a sprayer gun is to put the paint in the funnel.
If it flows through easily and quickly, it should work for most paint guns.
Step 5- Dilute more
If the paint struggles to get through the funnel, add one more part thinner until it flows.
One thing to keep in mind when using thinner is that it may lighten the color of your paint and take longer to dry.
In other words, since the paint is now thinner, you will need to apply more coats than usual in order to get the color and protective coating that you want.
And because of the longer dry time, you may have to wait a bit longer between coats as well – so be sure not to hurry and give yourself some extra time.
The amount of time and effort you will save by using a spray gun (as opposed to a brush) is still very much worth it, so you will most likely balance that out.
TIP: Never thin oil-based paint with water. Only use proper solvents for them.
Water-based paints such as acrylics can be thinned with water. But if you water down oil-based paints, it can cause a color shift.
This is because the water and oil don’t mix, the paint will first become lighter but quickly darken out on the surface as the water evaporates.
Why Use Oil-Based Paint in a Sprayer?
Now that you know what oil-based paint is and how to thin it correctly, it’s time to know why we are using oil-based paint in the first place.
Do we have other options?
You do, actually. Though, if you want to use a spray gun for your indoors, you’re more likely to use oil-based paint.
So, aside from latex paints being thicker, why choose oil paint if you have to thin it out anyways?
Well, the answer depends on what your needs are.
But in general, here’s why…
Oil paints provide a better protective seal than water-based paints, so the surface you are painting is shielded against dirt and grime, even mold and mildew.
Oil paints may be harder to clean up than latex paints and take longer to dry.
But oil paint’s durability usually makes it the preferable choice—especially if you are painting something that will tend to get dirty often (like a kitchen) or be exposed to nature (like an outdoor wall).
What is the purpose of thinning oil paint?
Oil-based paints being highly viscous, need to be thinned to reduce the viscosity of paint before you can use them in your spray gun.
This will avoid any clogging of paint in your sprayer nozzle.
Keep in mind that the paint from different brands and manufacturers may differ in their consistencies.
And if the oil paint you use is already thin (not very thick to clog the gun), you can use it without thinning.
Does temperature affect paint viscosity?
When thinning, keep in mind that the temperature at which you are working can affect the paint thinning process (and its viscosity) significantly.
As with most fluids, paint viscosity is inversely affected by temperature. This means as the temperature rises, the viscosity decreases, and as the temperature falls, the viscosity increases.
So, when you use cold paint, it will always appear to be thicker than it is. This can be most of the time deceiving when thinning the paint.
To avoid too much thinning and color differences, mixing the paint and thinner at room temperature is best.
This will ensure you get the desired results out of your oil paint thinning process without wasting your expensive paint.
Tips for Spray Painting Indoors with Thinned Oil-Based Paint
Before you begin spraying your newly thinned oil-based enamel paint or finishes like polyurethane, you must ensure the surface is adequately prepared.
If the area you are painting already has old paint, you must remove it or sand it a bit, followed by a coat of primer.
This is especially true if the surface has latex paint; it’s never good to paint with oils directly on top of latex paint.
Latex paint is water-based—and water does not mix well with oils, so your new oil paints will not properly adhere and apply to the new surface.
And that’s why we use a primer like Kilz!
The steps for thinning primers are very similar to the steps for diluting the paint itself.
But be aware that certain paints only work with certain types of primers, so ensure you buy the right combination at the paint store.
The Bottom Line
When spraying oil paint, the mixture you use in the spray gun must be thin enough not to clog the gun.
Always refer to the instructions on the can first. If the paint label does not explicitly state that it can be thinned, it is best not to do so.
But if required, follow the guidelines above and ensure you use the correct paint-to-thinners ratio for spraying.
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Jack Luis is a semi-retired painter who loved painting his clients’ ideas on their walls.
He had worked as a painter for over a decade serving customers in areas such as Charleston, Mount Pleasant, Beaufort, and Georgetown, SC (South Carolina). Today in his free time, he likes to read and write about the newer techniques implemented in his profession. You may read more about him here or get in touch with him here.