Painting clearcoat over a colored basecoat seems pretty straightforward. Yet, it’s one of the most confusing and misunderstood steps in the automotive painting process. There are intercoat clears, finish clears, matte clears, and more. What role does a catalyst or hardener play? Plus, there’s the fact that improperly applied clearcoats can ruin the previously applied paint. To get a better understanding, let’s start by breaking down the various kinds of clearcoats and how they are used and applied.
Basecoat clears are known by different names such as midcoat or intercoat clears. To know for certain, always look closely at the label on the paint can. Basecoat clearcoats are made with basecoat ingredients, not urethane. They’re products used for a variety of tasks. But in restoration and custom painting, they’re most often used as a base for creating custom candy and pearl layers over waterborne and solvent-based basecoats.
Basecoat clear allows painters to create multiple layers using special-effect pigments, powders, and dyes. They’re also used as a lockdown clear to protect graphic artwork paint layers. Basecoat clears are also utilized when blending paint repairs.
Never apply basecoat clear in heavy coats, like you would a urethane clearcoat. Here’s why: A urethane clearcoat has very little solvent in it. Basecoat clears sometimes have as much solvent as paint. Basecoat — any basecoat — is usually reduced one-part basecoat and one-part reducer.
The basecoat goes on shiny then turns dull, which means most of the reducer has evaporated out of the applied paint layer. When you think about paint, always remember the solvent needs to have time to properly gas out of the paint. This is the reason why most paints have a recoat window (time between coats). Paint product sheets advise users to allow basecoat paint to flash or turn matte before spraying the next layer.
Have you ever seen paint bubble up? This is usually caused by trapped solvents. In the case of heavily applied or too many coats of any basecoat, it can take days for the solvent to gas out. And, if urethane clearcoat is applied over that heavy basecoat, It gets trapped under the urethane and lifts it, causing a bubble or lifted area.
Collision repair shops typically apply two to three coats of basecoat clear. But restoration and custom paint shops will often lay down at least four to five layers. The more coats of basecoat clear applied, the longer it will take to dry. The reducer’s active-temperature range choice can also play a role. Sometimes, cooler or hotter temperature reducer will lead to better results.
Painting Basecoat Over Artwork
Not all basecoat clears are the same, as different companies produce different products. One company might want its intercoat or basecoat clear to have superior adhesion qualities, so the solvents in that product might be stronger than most. This makes the clear trickier to spray. Another company might have a product with solvents that aren’t as strong, which makes it easier to work with. The bottom line is, whatever clear you use, do your research and follow the product sheet for that particular product.
Catalyzed Or Hardened Basecoat Clear
You might have heard about adding a hardener to basecoats or basecoat clears. Hardener may be added to some brands of clear basecoat, but that doesn’t mean it becomes urethane clear. We asked Ron Peyton, a trainer at PPG about this. “Catalyzing basecoats and basecoat clears will always give the paintjob more strength and durability,” Ron explains. “But, it’s always optional. Once you add hardener to any basecoat, it gives it a much shorter pot life [time before it hardens in the spray gun]. Also, make sure you use the hardener designed to go with your basecoat clear.”
Basecoat clear is not meant to be used as a topcoat clear. A basecoat clear is always topcoated with clear urethane. If you use a basecoat clear for pearl or candy layers of a paintjob, you should apply several coats of urethane clear over it.
There are two main kinds of urethane clearcoats: high solids and universal (lower solids) clear. Both are great products and produce hard, glassy finishes that last for years. Most vehicles you see on the road are painted with universal or lower solids clear. High-solids clears are more expensive and are most often used on show cars and high-end restorations.
Solids are what’s left behind after the clearcoat has flashed (gassed) off. They’re mostly acrylic resin. The solid content refers to the amount of solids that remain as compared to the amount of solvents.
High Solids VS Lower Solids Clears
High-solids clearcoat has a higher concentration of resin and a smaller amount of solvent or VOC (volatile organic compounds.) Universal or lower solids urethane clear has less resin and more solvents. High-solids clearcoat has a smaller molecular structure than lower solids.
Think of it this way: you have two cans, one is filled with tiny bb pellets (high-solids clear), the other is filled with large marbles (lower solids clear.) Which one will be denser and have less air space between the items?
Basically, higher solids deliver a thicker, denser clear. Low solids is a thinner clear. High solids generally have more UV protection and a deeper appearance when compared to the same amount of applied coats of lower solids. Because higher solids are thicker, they’re great for use when trying to level out metallics, decals, graphics, and artwork. But, that thickness means they don’t flow as well as lower solids clear.
It also means higher solids are trickier to spray. The thicker the paint, the harder it is for it to flow. The painter has to lay the clear on heavy enough so the thicker clear flows but doesn’t run. If the paint doesn’t flow, you’re left with a bumpy, orange-peel surface. Painting high solids takes practice.
Lower solid clears are thinner, so they flow smoothly. This makes them a favorite for many home enthusiasts. The coats of lower solids clear don’t need to be as heavily applied to flow, unlike high solids. However, you need to apply more coats to get the same overall thickness as with high solids. If you plan to polish (buff) your clear, then you need the thickness. For example, if you use three to four coats of a high-solids clear, you have plenty of room to sand and buff. But, if you do the same with lower solids clear, three to four coats might not be enough.
Another consideration for the home user is their shops are not always as clean as painting in a professional paint booth. More coats of clear means more chances for debris like dark fibers to land in the paint. If you’re clearcoating over a light-colored basecoat, those bits of debris can show up more readily than if clearing over a darker or metallic color.
Another advantage of high-solids clearcoat is it has better surface stability. Less solvent has to be released from the sprayed surface because it has less solvent than lower solids clear. As the solvent is released from the paint, it affects the top surface as it pushes its way out. Urethane paint will appear nice and glassy right after it’s sprayed. However, sometimes, after it dries for a few hours, it looks a little dull. This is called dieback.
The ease of using Universal/lower solids clearcoats makes it a favorite for the home-shop painter. Plus, they are generally less costly than higher solids clear products. So, which should you use? For first time painters, it might be better to use a universal or lower solids clearcoat because it’s easier to use. Whichever one you choose, make sure to practice on a spare part. Learn on a test surface, not the surface of your project.
Using Urethane Clear As A Midcoat Clear
Can urethane clear be used as a midcoat clear? In certain situations, yes. For example, leveling out and protecting artwork and graphics. Say you’ve painted rally stripes on your Chevelle, and those stripes have a heavy edge to them. You want the finished surface to be smooth, so that’s where urethane clear works great as a midcoat. Urethane clear has more mil-thickness than basecoat. Plus, you can lay it on heavier.
Urethane also flows well, unlike basecoat clear. Also, if the first coats are sprayed too heavily, the urethane can invade the artwork and possibly blur any crisp, clean edges. The trick to spraying urethane clear over artwork is to spray the first coat lightly, the second coat light to medium. then, apply a medium to heavy coat, and finally a heavy coat.
As a custom painter, I use urethane clearcoat all the time as my leveling or midcoat clear to build up the paint level around graphics. There are two reasons I do this. The first is it allows me to build thicker coats of paint and level the surface faster. The other is the urethane clear acts as an insurance policy and protects anything under it. If I spill paint or make a mistake during rework over urethane clear, I simply have to sand it off. What’s underneath remains untouched.
If I’m working over a basecoat-cleared surface and the airbrush trigger sticks open, unwanted paint material can blast onto the surface. The solvents in that unwanted material can penetrate the basecoat clear, and even the color coats, beneath it. Because basecoat clear has a thinner-mil thickness than urethane, I could sand through it and into the color before the mistake is removed.
If you’re going to use urethane as a midcoat or filler clear, be sure to apply plenty of it. Also, make sure there’s good coverage over the entire surface. Urethane clear must be sanded before more material is applied in order for the new coats to stick. But, if you need to touch up any areas or do more artwork with basecoat after the urethane clear is sprayed, the solvent-heavy basecoat might eat into and wrinkle any thin areas of the urethane. Use care when applying the urethane and when sanding it. Don’t over-sand. Go easy on sharp corners and edges.
If you have an area where the urethane clear is thin, and you need to rework any artwork in that area with basecoat, apply the basecoat in very-light coats, and use as little reducer as possible in the basecoat. Problems might still pop up, and if they do, sand away any damaged material and try to repair it again. This is one of the reasons many painters only use basecoat clear over their artwork.
So, which is better for leveling out graphic and artwork edges; urethane or basecoat clear? There are pros and cons to each method. Some painters swear by basecoat clear; others, like me, will only use urethane. The best thing to do is to weigh the advantages of each system and find out what works best for you.
Here’s where your urethane clearcoat’s product sheet will come in very handy. Each kind and brand of clearcoat will have different requirements. The product sheet will tell which hardener/catalyst to use and how much of it is needed. Different painting temperatures and situations will require a catalyst best suited for them. Another way to ensure the best possible clearcoat finish is to use the right temperature reducer for your painting conditions. Slower reducers will allow the clearcoat to flow for a longer time.
Using Urethane Clear For Candy Coats
Some painters use urethane clear for their candy coats. They mix candy concentrates or dyes with the urethane clear. The glossiness of urethane clear allows you to see how the candy is layering on the surface (if it’s going on evenly or streaky). Always practice and test on panels before spraying your projects. Unlike testing basecoat colors, testing urethane candy-colors requires a larger surface.
Companies like Eastwood and House of Kolor make a line of candy urethane paint. These are a clear urethane premixed with the candy concentrates. However, once you’re familiar with how candy paint sprays, you can mix your own.
Another advantage of using urethane clear for your candy paint is some candy colors tend to bleed into the coats sprayed over them. This happens more readily with basecoat-clear candy paint. Let’s say you painted your Camaro with Candy Cobalt Blue and you want to paint white Rally stripes on it, and you mixed your candy blue using a basecoat clear. If you spray those white stripes directly over that candy blue, it will most likely bleed through the white, giving those stripes a mottled blue effect.
But, if you used a urethane candy blue and followed that with two coats of uncolored clear urethane, let it dry, sand it, and do the stipes, no bleeding will occur. But, that process takes longer. You would have to wait overnight and sand the whole surface before spraying your stripes. It’s a lot more work.
It can get confusing. That’s why it’s good to do as much research and testing as possible before using unfamiliar products and techniques.
Matte- And Satin-Finish Urethane Clearcoats
Painting clearcoat flat finishes used to be a tricky process. Painters would mix a flattening agent into the urethane clearcoat so it would dry with a dull finish. The degree of flatness depended on the amount of flattening agent used. The more flattening agent used, the duller the finish. Painters would have to test mix and spray those mixtures, keeping careful track of the amount of flattening agent used.
These days, many paint companies make a flat or semi-flat urethane clear with the flattening agent mixed in. These new clears provide a much harder and more durable finish than the old method. They hold up great to gas, are more scratch-resistant, and don’t stain as easily.
Eastwood’s Rat Rod Matte Clear is a painter-friendly matte-finish urethane clear. Other products, like PPG’s Ditzler Satin Clear, are very simple to use if you’re looking for a satin or semi-gloss finish. With some products like PPG’s Global D8115/8117 Matte and Semi-Gloss Clearcoat system, you can fine-tune the degree of flatness by mixing semi- and flat-finish products.
Ditzler, Eastwood, and Global low-gloss urethanes mix like a conventional urethane clear. But, the main thing to remember when spraying these finishes is the overall amount of flatness is determined by the number of coats, and how heavily those coats are applied. The heavier the paint is applied, the more gloss it will have. For example, if you want a very flat finish with no gloss, you might spray two medium coats of flat urethane. For a satin finish, spray the coats a little heavier.
Unlike glossy clear urethane, the flatness of the finish develops as the product cures. For example, say you’ve sprayed your last coat of flat urethane, and it’s still a little too shiny after an hour. After it sits overnight, more solvents will be released, and the finish will have the desired flatness. Remember this, when you’re spraying your test panels. Always let the test panel cure overnight before making a judgment about the finish.
The trick to spraying a nice and even flat finish is to practice. If you have dust or runs in the paint, there’s no rubbing them out. Rubbing on a flat finish will create a shiny area. That is another reason to spray a test panel and make sure your paint area is clean enough for your paint.
Next time, we’ll learn about buffing your finished paint. Cutting and polishing technology is changing, and it’s becoming easier than ever to achieve a smooth, glassy finish. Until then, good luck and have fun with your painting project.