What Sandpaper Grit Is Best Before Priming?

By: HowStuffWorks.com Contributors  | 

It's important to apply primer before painting because it protects the surface and enables the paint to adhere better. As a result of its chemical composition, the primer forms a binding layer, protects the material from mold and seals pores on the surface. Furthermore, primer eliminates stains and makes the paint job last longer. In addition, tinted primer can reduce the number of coats of paint you need to achieve a finished look.

Whether you're priming a porous substance such as wood or a smooth substance such as metal, you need to sand the substance beforehand. Sanding a surface removes the top glossy layer, allowing the substance to receive the primer. Without sanding the surface in advance, the new coat of paint won't stick to the previous layer. In addition to stripping the outer layer of gloss, you can also use sandpaper to correct imperfections and remove stains. Sanding ensures that the surface remains free of debris and that the finish is smooth and professional.

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You need to choose the sandpaper grit size according to the material you're preparing to prime. When sanding wood, for example, start with coarse sandpaper, such as 80-grit, gradually increasing in fineness. Each time you advance to a higher grit size, you eliminate the scratch marks from previous sanding. When sanding a softer surface, such as plastic, you may need to start with a higher grit size, such as 120, to avoid excessive scratching. For auto repair and other metals, start with 60-grit paper if you need to sand down below the rust to repair deep scars. Then increase the grit to 120 to remove rust stains or shape body filler. Finally, just before you are ready to apply primer to the metal, smooth the car's surface with a 320-grit piece of fine sandpaper.

Originally Published: Jul 25, 2011

Sanding Before Paint FAQs

Do I need to sand wood before painting?
Whether you are using lumber fresh off the market or refreshing an old piece of furniture, it is important to sand it first to remove any surface irregularities and the old paint. The goal is to prepare the wood to receive the new, fresh paint coat.
What is sandpaper used for in art?
Sanding blocks are often used to prime a surface to receive paint. Not only that, painters also use these blocks to help them sharpen their pencils, charcoal, paddles, and more to get the desired tip sharpness and angle. This tactic is often used by more experienced painters.
Do I need to sand primer before painting?
The goal of a primer is to stick to the surface and close any and all holes that could allow for mold growth, protecting the material itself and its surface. Old primers already in place hinder this effect and therefore to ensure a uniform layer, older coats should be sanded.
Should I sand walls before painting?
Not every project requires sanding. However, you should sand any holes you've patched or anywhere else you used spackle to make minor repairs. However, new drywall should definitely be sanded before it's primed and painted.
What grit sandpaper should I use before primer?
When looking to sand a surface before applying primer, the best grit sandpaper to use is 320 to 400. Both these grits can effectively remove the existing primer and help you flatten the surface.