The finish results you get from spraying paint depend as much on the thinning work you do as the technique you apply while using your sprayer! It doesn’t matter how careful and consistent you are if your coating material is inconsistent or spraying in an erratic manner.
In this short guide, we’ll talk through everything you need to know about thinning paints. We’ll be discussing both airless and HVLP spray guns, as well as the differences between working with latex vs. oil-based paints.
How to thin different types of paint
Latex paints are the most demanding when it comes to straining. They’re extremely viscous, so whenever you spray them with a handheld, HVLP, or small airless sprayer, you need to thin them down. Thankfully, it’s relatively easy to do. Unlike working with many oil-based paints, you can use plain water to thin latex compounds. Get yourself a measuring cup and a stirrer, and you’re good to go.
At minimum, you should plan to thin latex paints by 10%. Another minimum ratio that’s often used is 1/4 C water to 1 gallon of paint. That’s true when you’re using anything other than a big airless unit. If you’re using a handheld or HVLP system, you’re probably going to have to use as much as 20-30% water.
Oil-based paints (such as semi-gloss enamels) also tend to need some thinning. They’re far less viscous than latex coatings out of the can, but you can achieve a better spray consistency by thinning them down a bit further.
Always read the labels on the specific coatings you’re using to see what the maximum thinning ratio is. Check to see what thinners the manufacturer recommends, since you usually have to use some kind of mineral spirits rather than water. You’ll probably only need to thin these by 10% or so, depending on your specific sprayer, coating, and application.
Acrylic paints are water-based, so in theory they’re very friendly to added water. Since they’re water-soluble, though, you can’t add too much. Over-saturated acrylics flake or lose their bonding abilities completely. On absorbent surfaces, feel free to use as much as 50% added water. If you’re spraying onto something non-absorbent, keep your proportion well under 30%.
How to thin for different types of paint sprayers
These sprayers are designed to work primarily with oil-based paints. You can certainly use them with latex paints for indoor applications, but you’ll have to thin quite a lot. Start with 10% of water, and then work upward until you reach a sprayable consistency. Latex conditioners are also an option. These compounds give the effect of thinning without actually doing so. They decrease viscosity, which helps paint flow more easily without compromising its capacity to stick.
Any time you use an HVLP system, you should strain materials religiously. It’s a smart thing to do even on an airless system, to prevent any stray globs, but it’s a downright necessity with HVLP. Use a standard cone strainer.
Another tip for spraying using an HVLP system: HVLP turbines add heat to paint. It’s a key downside to the system, since it shortens the paint’s drying time (and makes it more viscous in your gun). You can negate that effect by adding a longer length of hose between your turbine and your gun.
Find current reviews of the best HVLP paint sprayers here!
Latex is right at home with an airless system. In fact, many airless systems are intended to work without any thinning! You can spray straight from a can or bucket. However, you should know that there are some caveats. We’ve found that the bigger pump systems can spray un-thinned paints without issues, but the smaller indoor units (especially under $500) are best used with thinned matrials. You don’t need to go crazy with thinning, though. Less than 20% water content should be more than enough. If you spray oil-based coatings using an airless system (and you rarely would be), you almost certainly don’t need to do any thinning.
To see which airless sprayers we recommend, head over to our buying guide to spraying latex paint!
How to know when paint is thinned sufficiently
This is where your viscosity cup comes in handy! You should get one with any good paint sprayer. A viscosity cup is essentially a glorified funnel. To test your thinned material, you pour some of it through the viscosity cup and check to see that it’s flowing smoothly. If it’s coming in globs or flowing unevenly, it needs to be thinned further. If it drips quickly like water, you’ve thinned too severely and will need to start again
Don’t follow any strict proportion when you’re thinning paints
It’s all about what works for you in the moment. Spray consistency depends on any number of things. It’s affected by air pressure, humidity, and the exact tip size you’re using on your gun. So, use our recommendations as a rough guide and then adjust based on how your actual spray results come out.
Tweak your proportions gradually, too. If you thin too far, you won’t be able to get coatings to stick properly. You can easily ruin a whole can of by adding too much water at a time. Thin gradually and test continually.
Always test your spray on something other than your work surface!
Keep a spare piece of something fairly smooth and similar to things you’d actually paint. Masonite is a good choice. Avoid something rough like plywood, since you won’t be able to judge the consistency of the paint coat with so much surface inconsistency in the first place.
Always use proper safety gear when working with paints of any kind.
Aside from harmless water-based acrylics, all paints are toxic to some extent. They contain chemicals which produce fumes that irritate both lungs and eyes. So, be sure to use an OSHA-approved respirator with a suitable chemical cartridge installed. You’ll also want to wear goggles to protect your eyes while mixing and spraying. Gloves are especially important when working with oil-based coatings, but they also save you having to scrub latex off.
Be aware that some kinds of paint aren’t meant to be thinned at all.
That’s true of quite a few oil-based materials. If you can’t thin your can, and it doesn’t spray well as is, you’ll need to apply it with a roller or brushes.
You can always change your spray tips!
As important as thinning is, it’s not the only factor that determines how well your coatings will spray. Opting for a larger tip size can also be pragmatic.