Do You Need To Prime Fiberglass Before Painting?

Ossiana Tepfenhart
by Ossiana Tepfenhart

Fiberglass is one of those materials that many craftsmen have a hard time with, at least when they first start working with it. This is especially true if you want to decorate it and add your own personal touch to your project.

Whether it’s a boat, a unique piece of artwork, or something else altogether, there will be times when you will want to paint your fiberglass. But, what’s the right way to paint fiberglass? Do you need to prime it?

You do not usually need to prime fiberglass before you paint it because it is already smooth. Some fiberglass is rough and you will need to sand it down and prime it before you paint it. Apply 1-2 coats of primer if you have rough or weathered fiberglass before you paint it.

People who are about to paint a fiberglass boat are probably wondering if they can cut corners by cutting out primer. Believe it or not, this is actually one of the rare times where priming won’t matter as much as it normally would. This guide will give you insight on why this is, and what you should expect when painting fiberglass.

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Do You Need To Prime Fiberglass Before Painting?

Generally speaking, fiberglass is one of the very few materials that takes well to paint without primer in some situations. This is why many boat owners don’t need to prime their boats before they give their vessel a brand new coat of paint. The reason why is fairly simple: fiberglass is smooth, nonporous, and works well with most paints.

With that said, many painting projects that involve fiberglass still tend to do better if they’re primed and painted. You may need to take a closer look to figure out what will work best with your project.

How To Tell If Your Fiberglass Project Will Require Paint

This is actually pretty easy. It’s all about the type of paint that you want to use. To find out whether the paint you’re using will need a primer, read the label. Most paints will say if they require a primer on the side of their can. If you’re using spray paint or latex-acrylic paint, it’s almost certain that you will need a primer.

What Kind Of Primer Should You Use?

Most primers will clearly advertise themselves as being usable for fiberglass projects. If you aren’t sure whether a primer is a right choice for the job, asking a sales clerk will help you make the right decision. You can also just search up the primer in question online to determine how good a fit it is for your project.

What If I Have Weathered Fiberglass?

If you have weathered fiberglass you can still paint it, but you’ll have to clean it up first. You can clean the fiberglass with some warm water and soap. You’ll need to rinse it afterward, of course, to remove any residue from the soap. After you clean it, you will need to let it dry and then apply some polishing compound to it so that it takes off the oxidized layer.

Polishing compounds contain abrasives that allow them to work just like fine sandpaper. So, you won’t need to worry about getting sandpaper pieces when you use a polishing compound. After you wash the fiberglass again, then you can apply the primer and paint to your fiberglass.

Can I Remove Oxidation With Vinegar?

Yes, you can definitely remove oxidation using vinegar when you use it on fiberglass. Although, the homemade solution will only work if the problem is not significant. So if you have a significant problem, you’ll want to make sure you use something else instead of vinegar.

You can also use vinegar for any mildew, mold, or old scum lines on the fiberglass. It will help remove all of this, kill the spores or any bacteria or fungi, as well as remove the oxidation. If you’re removing mold, and bacteria as well, you’ll need to make sure you put some gloves on and cover up your skin so that you can avoid getting these toxic substances on your skin.

Prepping A Fiberglass Surface For Paint

If your goal is to get a smooth, professional-looking finish, then prepping fiberglass is usually the best thing you can do. Here’s how to do it:

  • First, make sure that your environment is right for painting. You don’t want an environment that’s too humid or too cold. This can turn paint and primer tacky. Your ideal environment will have no more than 60% humidity, and will be between 65 to 90 degrees Fahrenheit. If it’s too warm or too cool outside, it may be better to wait until your conditions improve.
  • Cover your area with newspaper, and remove any metal fixtures that you don’t want to have covered with paint. No one likes having to scrub paint off surfaces that become prone to a spill. This is just a quick way to reduce the amount of spillage you have to deal with.
  • Thoroughly clean the surface that’s going to be painted with soap and water. This ensures that paint won’t stick to any leftover grit and grime that may be stuck to the surface. Before the next step, rinse off the surface with water.
  • Grab some sandpaper and buff the surface. You should try to use 150- to 400-grit sandpaper for this task. The sandpaper will buff away remaining paint and also give your fiberglass enough traction for new paint to stick well after priming.
  • Get rid of any remaining dust. You can use a tack cloth for this step. Make sure that your surface is as dust-free as possible before continuing to the next step, since extra dust can change the texture of your paint.
  • Mask off any remaining areas to avoid with painter’s tape. Make sure that the tape covers the entire surface. A tight seal is ideal, since paint can leak out through crevices.
  • Grab a primer that is compatible with your paint type, and apply a coat of it over the area you want to paint. You can find out which primers will work with your project by reading what types of paint they work with on the side of the can. A typical project will require one to two coats of primer.
  • Give the primer time to cure. This can take anywhere from a couple of hours to a couple of days. Like with all other steps in this guide, you can always refer to the primer can to find out the curing time.

From here, you can paint your fiberglass and apply a topcoat. Just like that, you’re done with your painting job.

How Long Does Prepping Fiberglass Take?

If you’re like most DIYers, you probably have a set amount of time that you can complete a project in. Knowing how to budget that time is important, simply because you want to be able to get on with your life. Prepping a fiberglass surface is something that can be done within a day or so.

Seems like a long time to wait, doesn’t it? Well, there’s some good news. Actually painting fiberglass and adding a topcoat doesn’t take as long. All you need to do after is let your paint dry, add another coat, and then add your topcoat. So this is actually the bulk of your project’s time.

Do You Always Need To Sand Down Your Area?

This is a little tricky. This is one of those things that hinge on the type of primer that you use. If you decide to spend extra money on a no-sand primer, then you can skip the buffing stage of your prep. If you’re not a fan of sanding, this is a good investment to make. Your painting results will be the same regardless.

Sealing Fiberglass

If you’re wanting to seal your fiberglass, you will need to use a waterproof epoxy sealant that is meant for steel, fiberglass, wood, aluminum, or concrete. You will need a good quality brush, sponge or roller to apply it correctly and evenly. Make sure you get the 10 mil prime coat. It doesn’t shrink, and it’s super flexible using just one application.

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Our Final Take

Figuring out whether or not you should prime your fiberglass prior to painting it isn’t a “cut and dry” situation. In many situations, such as painting a boat, you can probably do without a priming session and still see good results. On the other hand, if you’re using spray paint or latex-acrylic paint, getting a primer is a must. It’s the only way to make sure you get professional results.

That being said, having to prep and prime your surface doesn’t have to be an intimidating endeavor. As long as you’re willing to clean, buff, and tape away areas that shouldn’t have paint, you should be alright. The process itself may be time-consuming, but it’s really not that hard to do. So, don’t let it stop you from doing your own fiberglass paint job. Even a beginner DIYer can do it.

Ossiana Tepfenhart
Ossiana Tepfenhart

Ossiana Tepfenhart is an expert writer, focusing on interior design and general home tips. Writing is her life, and it's what she does best. Her interests include art and real estate investments.

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