The secret to flawless automotive paint lies equally in the painting techniques and sanding methods you use throughout the entire process. However, it’s important to know when to sand between paint layers and, more specifically, which layers to sand between, to achieve a smooth, blemish-free finish. Without this key knowledge, you’re bound to spend more time and energy sanding without much to show for your effort.
Knowing when to properly sand between paint layers requires an understanding of which potential problems sanding addresses and which types of sanding are needed to resolve them before they mar the final product. Below, we’ll cover everything you need to know about alternating sanding and painting to clarify common misconceptions and help you improve your techniques. When you’re ready to stock up on sanding materials, trust the products from Colors Edge to get the job done right—the first time.
What does sanding a car accomplish?
Even as advanced as automotive painting processes have become, there’s still a need to sand body panels before they’re painted to ensure more than just an aesthetically pleasing finish. The abrasives used to reduce the imperfections in the bare metal, primer, base coat, and clear coat—assuming a basic paint job—contribute to a better result once the car’s fully painted. Here’s what sanding a vehicle allows you to accomplish:
- Reduce surface imperfections
- Remove contaminants trapped within the top layer
- Create a textured surface for the primer and paint to adhere to
- Provide an even and uniform foundation for subsequent primer and paint layers
Properly sanding a car takes hard work, whether you’re prepping a small coupe or a boat-sized classic. The key to making the most of your sanding time is knowing when to pick up the sandpaper to accomplish a particular goal. Before we get too deep into when you should sand between paint layers, let’s clarify the difference between wet and dry sanding and play out a scenario you might have found yourself in before.
What’s the difference between dry and wet sanding?
At the most basic level, the difference between dry and wet sanding lies in whether the sandpaper is dry during use or immersed in water before being applied to the sanding surface. Most dry sanding occurs in the early stages of paint preparation, while wet sanding occurs after paint layers have cured and set. Wet sanding is also called color sanding.
Sanding automotive panels with dry sandpaper allows the abrasives to work quickly and effectively. It’s commonly used in painting to smooth out panels before they’re primed and painted, or during blending processes on single or multi-panel paint repairs. In contrast, the lubrication involved in wet sanding is ideal for removing oxidation, swirl marks, orange peel, and surface scratches.
What happens when you don’t sand a car before painting?
If you don’t sand a car before you paint it, you’re going to end up with some of the most common paint problems that lead to extra work in the paint booth. After hours of labor, you’ll likely find visible imperfections that interrupt an otherwise even texture. In the worst cases, the paint will begin to peel, flake, or even separate from the car panel completely.
Why shouldn’t you sand between certain paint layers?
Generally speaking, you typically don’t sand between individual layers of a single step in the automotive painting process, from laying down primer and base coats to finishing off with clear. If the layer is still soft, sanding it compromises the structure as it cures. You’ll not only gum up your sandpaper, but you’ll also have to remove what’s there and start over.
Much of succeeding at automotive painting requires trial and error across multiple paint jobs, at least in the beginning. However, learning these techniques the easy way (compared to the hard way, which often comes at the cost of a professional or even hobby paint job) lets you head off common mistakes before they happen. Experimenting with sanding between layers using a small test panel can help you recognize when sanding between paint layers works in your favor and when it’s not worth the elbow grease.
When to sand between paint layers: A comprehensive guide
Distinct use cases allow for sanding between paint layers to improve the final results. For example, you may need to lightly sand between base coats to remove surface contaminants that could jeopardize additional coats you spray, but the same theory doesn’t apply to primer or clear-coat layers. Below is an overview of when to sand between paint layers, depending on which step you’re at in the painting process.
Primer layers
The amount of sanding you do and the type of sandpaper you use depend on the kind of primer you lay down. If you’re using epoxy primer, you’ll typically need to use 400-600 grit sandpaper to level runs and imperfections and improve adhesion for additional coats. With a high-build primer, you’ll need to be more aggressive and use 320-400 grit sandpaper to remove orange peel and similar imperfections.
Base coat layers
Should you choose to sand between base coat layers, you must apply an additional base coat layer before moving on to the next step. Most automotive painters only sand between base coat layers—using 1200-2000 grit sandpaper—to remove surface imperfections or contaminants. Otherwise, a quick once-over with a tack cloth will suffice.
A note of caution: if you spray a metallic flake or pearl, sanding those paint layers will alter the resulting effect, creating a distinct difference between where you did and didn’t sand. In addition, if you sand through the clear coat to the base coat in one or more spots, you’ll need to seal those areas and apply another base coat before laying down the clear; otherwise, you’ll induce solvent pops that separate the existing base and clear coat layers.
Clear coat layers
Sanding between clear-coat layers is uncommon unless you need to address contaminants that could compromise a clean finish. In most cases, you’ll color sand the final layer of clear coat to create that fresh-off-the-assembly-line look (and have applied an additional layer of clear to account for this post-painting process).
However, you may also need to sand the top layer of clear coat to blend panels if you’re matching a nearby repaired panel. A mix of hand and power sanding helps achieve an even surface that you can then spray base coat and clear coat over to blend the repaired panel into the remaining panels.
Important tips to keep in mind as you sand paint layers
Discussing when to sand often brings up a related topic, i.e., hand sanding vs. power sanding. When sanding by hand, remember to apply even pressure across the surface so you don’t create valleys where you pressed harder than in other spots. However, sanding by hand can make it easier to blend edges and body lines.
Power sanding cuts the time you’ll spend on larger panels in half (or more), but it can be a double-edged sword. Keep away from edges and sharp body lines when using this sanding technique, as a power sander can easily cut down to bare metal. There’s something to be said for taking it slow, even if you are using a power tool for this work.
Sand with confidence and the right tools with Colors Edge
The time you spend behind a power sander or with your hands cupped behind a block of sandpaper can significantly impact your automotive paint jobs, whether you stick to factory paint or branch out into custom paint jobs. With more knowledge surrounding sanding techniques under your belt, the paint booth and your next project await. Contact us or call us at 336-378-7872 to order your supplies or ask any questions you might have about sanding your next masterpiece for show-stopping results.
