How to Sand Fiberglass: 7 Tricks & Tools to Get Smooth Finish

Fiberglass is great for styling. That’s the entire essence of it. Sanding it for extra shine or style is going to give it another awesome look and feel. However, before we begin. There’s something that must be said. Sanding fiberglass should be something that you do with caution.

It is capable of getting into your skin and if you have used it before without properly covering your skin, you will know how itchy and uncomfortable it makes you feel. It is also dangerous to your eyes and to your respiratory system. Well, with that said you can now move to how to sand fiberglass.

Before we hop right into the process of sanding fiberglass, there are certain important things that you must know they include the “fiberglass sanding tools” section in this article that you must use whenever you sand fiberglass.

How to Sand Fiberglass

Before going to sanding the fiberglass you need those material or tools:

  1. Sandpaper [100 to 220 grit]
  2. Hand Sanding Block => Check on Amazon
  3. DA Sander or Orbital sander
  4. Glazing Putty
  5. Grease Remover (or wax)
  6. For Safety: Gloves, Respirator

Now that we have all the tools ready what should be the next step to take? You have a lot to learn from this article, from how to sand a fiberglass boat for paint, how to be safe while sanding, and sanding fiberglass resin. Before we go into the details for all that, let’s first take the right steps to sand out fiberglass.

7 Steps of How to Sand Fiberglass Effectively:

Since we have quickly acquainted ourselves with what fiberglass really is, the adverse effects that the dust can have one your skin, eyes, and respiratory system, we can now head on to the steps to take in order to neatly sand the fiberglass.

1. Place the fiberglass under the sun to cure

For a better, faster, and easier process of sanding, you must leave the fiberglass in the sun for some days, at least 5 or 6. You have to do this if you want to create a fine and smooth finish for your fiberglass. Because the fiberglass catalyst would stay on your fiberglass even for some days or weeks after the parts have been made.

Place the fiberglass under the sun

Why do this?

New fiberglass would originally come with Gelcoat on its surface. The Gelcoat is used when making the fiberglass components to line the molds. Allowing it to cure for some days will enable the fiberglass to release any excess and unwanted air that’s holding the Gelcoat in place. It will make the sanding process much easier. This is just a simple method of getting the job done faster and easier.

2. Join all the parts

This isn’t necessary for those that are only trying to sand totally separate fiberglass. However, if the fiberglass you’re about to sand is a part of a bigger work like a car, a door, a boat, or any other thing, it would really help you if you join all the pieces.

This is going to help you easily smoothen edges that go into other parts. Doing it separately may require you to eventually have to focus so much energy on cleaning the edges out, so why not just do it now.

3. Clean with grease remover (or wax):

Clean with grease remover
Cleaning with grease remover [Wax]=>
Remember curing the fiberglass in the sun? Well, now you have the release agent on the fiberglass and the most effective way to get rid of it is by applying a grease remover and/or wax or paint thinner to clean it.

4. Start the Sanding process

You have taken all the important steps, now it is time to begin the task. Before you start, you must ensure that your sandpaper has the right coarseness for the surface you’re trying to sand. The following should help you make a better decision:

using 80 to 200 Sandpaper Grits in fiberglass
using 80 to 200 Sandpaper Grits=>

a)Using 80-100 grits: if you’re starting out with the fibreglass and the surface needs some rough peeling, you should use sandpaper with up to 80-100 grits. This will help you get excess machining marks out of the fiberglass surface.

b)Using100-120 grits: it’s time to go for much finer sanding. When the marks are cleared, now it’s time to make the surface smooth to the touch. It’s advisable to go at it gradually. It makes the job easier and less time-consuming. This may not give the thorough smoothening but that is the plan.

c)Using 150-220 grits: this is where you’ll have to make your own choice depending on the level of smoothness that you desire. If you’re looking for an entirely smooth surface, you go for a higher grit.

The basic idea is to start small and gradually drive it bigger. At the end of the day, you should have a fiberglass surface that’s just as smooth as you intended.

5. Fill low spots

Car Putty Spreaders Set Auto Body Scraper Filler fiberglass
Use Fiberglass Filler / Putty =>

Because you’re human, and you could mistakenly file some spots too deep while using the coarse-grit sandpaper, you would need a glazing putty which should help you to refill those spots so that you can sand again for a better outlook.

6. Spray your Primer for finishing

As soon as you finish sanding with the coarse-grit sandpaper, you should apply primer to the surface of the fiberglass. This will enable you to smooth filing to be more effective.

7. Do the finishing

Finally, you can now sand the fiberglass with a much smoother sandpaper. One which is less coarse as the one that was used for the initial sanding process. After this process has been completed, you can have your fiberglass under the sun again for some time.

Going on about how to sand fiberglass, whether you’re sanding fiberglass boat for paint, or you’re just sanding a small piece of fashion tool, the above-listed steps would greatly help you.

Pro tip: if you’re going to be filing small fiberglass, it is advisable that you use your hand for sanding. Sanding with a machine would reduce your flexibility and control. Also, remember to always file with the same amount of pressure, and I upward and downward stroke for a more even surface.

Don’t forget that if you are sanding fiberglass, there’s a high tendency that you’re going to have some of the dust or particles in the air. You must ensure that you have your respirator on always.

Fiberglass Sanding Tools:

Before you begin to sand your fiberglass you must make sure that you readily have some of the following tools or the job is going to be extra difficult, strenuous, or even impossible.

Note that some of the tools may not be necessary, depending on your workspace, your work schedule, and other possible factors. But in order to keep yourself safe and make your working process a lot easier and faster for you, you must get the basic ones.

Power Tools [Sander]: The sander is what helps you smoothen or peel off the surface and excess paint on the surface of your fiberglass. A good sander should be able to help you sand through your fiberglass smoothly and with good aggression. It also should be able to collect the dust and send it to the vacuum.

Types of sanders and when to use them:

Now that you know exactly how to choose a good sander, let us look below at some of the amazing sanders that are out there and when to use them. It may interest you to know that there are over 15 types of sanders, so you should try to choose the one that best works for the kind of project you’re undertaking.

a) Random Orbital sander:

There is a strong chance that when you go to an equipment store asking for a sander, this is the first one that would be thrown at you. It is the most common type of sander and it is used mainly for creating a smooth finish on the fiberglass surface. This is usually preferred for sanding wood but sometimes could be used for fiberglass.

Random Orbital Sander for Fiberglass sanding
Random Orbital Sander=>
b) DA (Dual Action) sander:

This is the one that majors in fiberglass sanding. As a matter of fact, if you get to a tools shop and ask for a fiberglass sander, you’re most likely going to be handed this one in particular. It is durable, lightweight, powerful, longer-lasting, manages dust, and finally, it collects dust. It is a bearer of completeness.

DA sander best for fiberglass
Professional DA Sander=>
Why is DA (Dual Action) sander the best for sanding?

Just looking at the name, you would already easily see that it provides double action and makes sanding more efficient.

  • DA sanders let you reduce the physical strength you invest in the work. You would only need to carry the sander and the work goes smoothly.
  • Time management. It is faster when you use DA sanders. You only have to be careful of the amount of force you place on the fibreglass surface.
  • Easiness of use: you can make use of a DA sander for both rough and smooth surfaces. Most DA sanders even come with a palm grip which makes it a lot easier to handle.
  • DA sanders cost less: unlike other sanders that may tear your wallets, DA sander gives you variety. This means that you can buy one with a smaller size but with the same level of power. The deal is that the bigger the sander, the higher the cost. Even at that, they’re still some of the cheapest.
How to use orbital and DA sanders
  • Turn the sander on and don’t place it on the surface just yet.
  • Leave it to rotate until it reaches the maximum speed that is required for sanding.
  • Gently place it on the surface you’re trying to sand. Make sure you don’t press it on the surface or you could create depth on the surface that would ruin your work.
  • Before you turn off the sander, make sure that you have lifted it off the fiberglass or you would make a mess of your work.
  • Don’t use the sides of the sander even if you’re trying to sand a deep edge. Use your hand sandpaper to do that.
  • Ensure that you move the sander from left to right on the surface of the fiberglass. This is safer to avoid making the surface look uneven.

c) Belt sander

This one is perfect for smoothening wood materials. Although you can use it for your fiberglass in some situations, it is more preferably used for smoothening wood. It is also used for smooth finishes.

d) Detail sander

If you have ever tried to sand a deep small edge where your huge sanders can’t reach, then you would know the importance of this one. Many professionals choose to have one of the huge sanders and still keep this one in case they need to sand some deep edges.

There are several other types of sanders but I want to save you the stress of looking too hard for the best and that is why I have suggested the ones above. Must Read: 7 Ways for Sanding Concave Surfaces Fast.

Other Hand Tools Required:

Before you begin your sanding at all, you must ensure that you have some of these tools. They’ll make your job much easier for you.

a) Sandpaper

Whether you’re doing the job manually or with your machine, the most important tool that you must have is the sandpaper. You want to get one with some roughness that allows you to scrape off any excess property that you don’t want on your fiberglass. After that, you can move on to much finer grits. This will be explained later in the article.

When to use sandpaper grit?

There are contours and edges where your orbital and DA sanders won’t be able to reach. You would need to use a piece of sandpaper for reaching those edges so as to get an overall clean result.

b) Sanding blocks

It is common for some people to just fold the sandpaper and begin to sand their surface right away. However, it is so stressful that way. To make the job easier for you, you’d need to purchase a sanding block that allows you to have a more balanced grip on your sandpaper.

Sanding blocks also eradicate the discomfort you’d feel from pressing the coarse sandpaper surface on your hand.

c) Abrasive sponge

An abrasive sponge helps you to clean out contours and deep edges. A good one should be able to adjust with the shape of the material you’re trying to clean.

d) Wax and grease remover

This is going to help you get rid of the release agent.

A glazing putty: this will help you refill low spots.

e. The vacuum

For the sake of your health and so that you don’t have the dust in your skin and in your respiratory system, getting a sander that collects dust is advised. you should use the vacuum that’s good to store the dust almost immediately so that you can transfer it later on to a dustbin when it’s full and you can continue to work.

f. A gallon

You will need this for storing the dust. Now, even if you don’t think this is necessary, you should know that the fiberglass dust can be used for another purpose and this is why some experts decide to collect the dust inside a gallon.

g. A coverall

You may not think this is important but no matter how good a vacuum is, it can almost not collect all the dust. You need to hear a coverall to protect your skin.

h. Respirator

For those of you who work in an enclosed building, you know that the fibreglass dust is caged inside the building. Staying inside the building is going to be risky to your respiratory system. This is why you must at all times have a respirator on.

Other things you might need for your sanding would include the following:

Sanding board: if you’re sanding a flat fiberglass surface, this tool is a must-have. It will help you keep the fiberglass in place when you begin to sand.

A rubber sanding block: for curved surfaces, this will help you easily place the sandpaper on any fibreglass of any shape ready for sanding.

What do you do to keep yourself safe?

A lot of people go headlong into the sanding process without clearly calculating the risks, as well as, the effects that the procedure is going to have on them. In this line of work, your safety should be given paramount importance. A lack of care for your own health could hinder your work entirely and make you completely ineffective.

The fiberglass sanding process is capable of depositing particles of the fiberglass in your eyes, on your skin, and most dangerously, inside your lungs. This could lead to some really bad health conditions. You have to ensure that you minimize the risk and increase your sanding fiberglass safety.

Some of the tools and equipment you’ll need for that would include the following:

  • Gloves: for the safety of your hands and fingers. Gloves don’t only help you to prevent dust from touching your hands, they also help you to reduce your risk of getting your fingers cut or injured.
  • Coverall: for your entire body
  • Respirator: masks for protecting you from breathing in the fiberglass particles

If you have gotten all three of this equipment, then you can begin to work but you must know that these may not be enough to stop some occupational hazards.

You could trip or cut yourself with the sander or grinder, you know how all these things work so you must make sure that you always have your first aid box with you at all times.

For more safety measures, there’s what we call a workspace, or a work area. This is where you carry out your work on a daily basis. That space should be free and manoeuvrable. You don’t want to always have to kick your tools and equipment out of the way every time you have to walk around.

Having an orderly and organized environment for work is going to greatly affect your productivity level. It’s also going to make your job a lot easier and more fun.

Pro Tip About Tools:

Have a shelf in front of you where you can easily pick and drop your tools. If you can’t afford the shelf, you can get a toolbox that lets you properly arrange your tools in an orderly fashion.

Final Words:

Sanding fiberglass resin is just as important as filing any fibreglass material. You don’t want to end up with a terribly rough and uneven surface and that’s why sanding is very important.

In order to give your resin a smooth and very even outlook, you must follow the steps which have already been listed earlier in the article. But because resins can be different in size and shape, you have to use a sanding block. This should enable you to wrap your sandpaper around it and give you a good and comfortable hold on it.

In conclusion, always remember that in any sanding process you carry out, your safety and health come first. Sanding fiberglass with your skin open is going to result in an itch. If it gets into your eyes, it could result in some complications in the long run.

Also, remember that without the appropriate tools, your work is going to be greatly impeded. You don’t want to start filling a giant boat with just your sandpaper and your bare hands. You must get a sander or grinder that makes the job a lot easier. Well, I hope all these tips were helpful.

Last Updated on February 1, 2021 by Rogers Weber

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