Sanding removes imperfections and smooths the surface to help the paint stick better. So, should you sand between coats of spray paint?
Sanding between coats of spray paint is optional. That’s because spray paint is applied at a high-speed and has impressive bonding qualities. But, if you want a smooth finish, you must sand between coats.
To sand between coats, use fine-grit sandpaper only. Medium or coarse-grit sandpaper will remove the finish instead of smoothing it.
Spray Paint Dry Time Before Sanding
Spray paint must dry for one hour before sanding. This gives the coating enough time to harden and dry to withstand the sandpaper pressure. However, the dry time of spray paint depends on the humidity levels, paint type, and the number and thickness of coats.
For instance, you can sand water-based spray paint sooner than oil-based paint. Water-based paint will dry faster because its solvent (water) evaporates faster than oil.
If you sand spray paint too soon, you will ruin the finish. That’s because a wet spray paint coating hasn’t bonded to the surface, and if you swipe sandpaper over it, the finish will be removed. The sandpaper will also get clogged over a wet coating.
To know if the coating is dry enough for sanding, swipe fine-grit sandpaper over it without applying pressure. If the sandpaper gets clogged, the coating is still wet and not ready for sanding. On the other hand, if the sandpaper goes smoothly over the surface, the coating is dry and strong enough to withstand sanding.
Sanding between coats of spray paint isn’t necessary. That’s because spray paint is applied at a high-speed and has impressive bonding qualities. The spray paint penetrates the surface deep and sticks to form a smooth coating.
However, if the previous coating was applied more than 24 hours ago, you must sand it. That’s because spray paint attracts dust and filth to its coating while drying. If the coating has dust and filth, the new coating won’t stick properly because dust prevents paint adhesion. So, you must clean and sand to remove the dust to allow proper paint adhesion.
You must also sand if the old coating is riddled with bumps or imperfections. Fine-grit sandpaper will remove imperfections and bumps from the coating, leaving behind a smooth and even layer.
For oil-based spray paint, sanding between coats is necessary. That’s because oil-based spray paint has a glossy finish that repels liquid, including paint coating. So, you must lightly sand the gloss off the coat to allow the second coat to stick properly.
You shouldn’t sand the last coat of spray paint. That’s because the last coat of paint must have a glossy finish to protect the surface underneath. So, if you sand the last coat of spray paint, you will remove the glossy finish, and the surface underneath won’t be protected.
You should only sand a paint coating if you want to apply another coating over it. Optionally, you can sand the final coating if you want to apply a protective top coat over it. But, this isn’t necessary because a top coat (sealant) will stick over spray paint regardless of whether you sand.
You can also sand the spray paint if you want a distressed finish. A distressed finish is achieved by sanding the final coat so the finish looks old and worn out. However, ensure to only sand the final coat with fine-grit sandpaper.
Sanding Before Applying Spray Paint
You need to sand before applying spray paint. This is to remove imperfections and bumps from the surface before the spray paint is applied. Also, sanding helps to remove dust nibs and grain that can cause a bumpy finish.
When you sand, the abrasive side of the sandpaper removes bumpy layers off the surface that can cause the finish to look uneven. Sanding also creates tiny ridges on the surface that the paint can penetrate and stick to. This help with paint bonding.
Also, if you spray paint over an existing finish (especially oil-based paint), you must sand it to remove it. You must remove the glossy sheen of the previous finish before applying spray paint. If you don’t, the spray paint won’t stick.
To sand the surface, use medium-grit sandpaper to remove bumps and imperfections. Then, finish with fine-grit sandpaper to smooth the surface.
Here are the cases you don’t need to sand before applying spray paint:
- If the surface has no bumps, cracks, or holes and is smooth.
- If you apply paint primer before painting.
- Don’t sand over a clean surface.
- If you need a quick fix.
Wet-sanding won’t remove fully dried (cured) spray paint. That’s because fully dried spray paint is bonded to the surface, its solvent has evaporated, and the coating is strong and durable enough to withstand water and sandpaper.
Wet-sanding is a type of sanding where you use water and waterproof sandpaper to sand. This type of sanding prevents dust and gives smoother results than dry-sanding. But, if you wet sand spray paint that hasn’t dried yet, you will remove it.
So, wait 24 hours for the coating to dry fully (cure) before wet-sanding. This gives the paint particles enough time to harden and compact to withstand water without getting removed.
Spray paint has impressive bonding qualities, so sanding between coats is optional. However, you must sand before applying spray paint. That’s because sanding will remove imperfections and bumps that prevent good paint adhesion.
You shouldn’t sand the final coat of spray paint unless you want a distressed finish.
Tony is a professional painter and an author of DIY Geeks. Tony has completed over 1,000 painting projects for his clients. It's safe to say he knows what he Is talking about,