How To Sand Fiberglass? – Detail Oriented Explanation

Fiberglass use is increasing day by day as people are more inclined towards cheaper and lightweight products. Consciously or unconsciously, you must carry items that are of fiberglass. Its use is getting more common as the days go by. After the inauguration of the use of fiberglass in the commercial sector in the 1930s, its uses have been accelerated increasingly.

Commercial companies are using fiberglass in many sectors. It is hard to believe the extent of the use of fiberglass in so many sectors from an early perspective of the 20th century. So, how to sand fiberglass? You can imagine why the companies are producing so much of this substance and why it is getting so popular among the customers. Let us have an observation at its benefit first.

How To Sand Fiberglass

How To Sand Fiberglass – Full Guideline

Fiberglass provides much more specific resistance than other metals. It is more efficient in this regard in the case of the most popularly used steel. So, it is being used in many types of equipment involving electricity. As fiberglass has more specific resistance, it is a better insulator. It can often be used as an insulator and is therefore suitable for much electric equipment and materials associated or adjacent to electric equipment.

It is more resistant to any kind of fire or flames. It does not catch on fire easily. If burnt, it does not emit harmful fumes, making it ideal for use inside the house. It can be a mixture of organic materials and so is easy to incorporate. Fiberglass is not affected by different kinds of insects or is not very much affected by moisture.

So, the durability of these materials is generally higher than many other materials. Fiberglass is very light in weight in comparison to metals or other building materials, which makes it convenient to use. The usage of fiberglass has the increment for the benefits mentioned above. Due to its increased usage, it will not be unwise to assume that fiberglass has encountered in your daily life. You may also need to maintain it in some ways.

Fiberglass is used in various industries. It is used in many manufacturing materials. Besides that, it is being used in car washes, cooling towers, power generation, pulp and paper industry, plating plants, and many more. Now, you might wonder about the process of getting accustomed to these materials. If you pay attention, you may find various types of materials around you which may contain these fiber glasses. Your cars can have a fiberglass body.

Though it is not as popular as other metals, fiberglass is used in the automotive industry. Unlike having the whole car body made of fiberglass, you may very well find extensive use of fiberglass in different body parts. You can find many body parts as replacements. Various kits and customized parts that are made of fiberglass are also available.

It is used in various electronic devices that you can hold and use every day like cellphones, computers, radio, TVs, etc. It is very common to use fiberglass in boats and other marine transports. It is used in boats for its lightweight and low cost. Your bathroom appliances can also be made out of fiberglass. It is often used in bathtubs. It is also used in shower trays.

So, considering such extensive use of such materials in our everyday life, it is safe to assume you have used something made out of fiberglass. Now, whether it is on your car, boat, or bathroom, you may feel that it is necessary to sand the fiberglass. Sanding the fiberglass will smooth the surface of your fiberglass. It will also help you give a different shape on the surface. It will give your fiberglass material a shiny and smooth surface.

It is to be remembered that sanding the surface of fiberglass can be a little bit tricky. But it is not an impossible task. You very well do it yourself (DIY) at your very home. You just need the right instructions, proper tools, and a good work ethic. Here, we will cover all the possible aspects you take for granted while choosing the right tool. Right Sandpaper.

How To Sand Fiberglass Safely:

Sanding fiberglass can be a tricky business – if done incorrectly, it can lead to serious injuries. To ensure a safe and productive job, follow these simple tips:

  1. Wear a mask and goggles to protect your lungs and eyes.
  2. Always stop sanding when the surface becomes blisteringly hot – this means you’re going too far!
  3. Use an electric sander in a well-ventilated area in accordance with the manufacturer’s instructions.
  4. Make sure the surface you’re working on is completely clean and free of any dust or dirt.

Skin, Eye, and Respiratory Protection:

Sanding fiberglass can be a dangerous job, and it’s crucial to take all the necessary precautions to protect yourself. Make sure you have all the right safety equipment before beginning – including respiratory protection, appropriate skin, eye, and mouth protection, and gloves.

Always wear a respirator with a HEPA filter if you’re going to be working with high concentrations of dust or wood particles. And last but not least, always take care while sanding fiberglass! However, it’s easy to get sandpaper embedded in your skin and eyes, and it can be difficult to remove them. Stay safe and sand responsibly!

Is Sanding Fiberglass Difficult?

Sanding fiberglass can be a relatively easy task, but it can be time-consuming depending on the size of the area to be sanded. Make sure to factor in the time needed to sand the area by using coarser or finer grit sandpaper, and take care when handling the fiberglass.

It’s also important to test an inconspicuous spot first to make sure there is no hidden damage. If all goes well, then it’s time to start sanding! Be sure to use caution when sanding fiberglass, as it’s delicate and can easily break. Have fun sanding, and be sure to share your results in the comments below!

Why Sand The Fiberglass?

It may not be unnatural if the question comes to your mind: Why should you sand the fiberglass. In which circumstances you might need to do it. After constant use, your paint on the surface of the fiberglass may come off. Or you may want to alter the color of the surface to change things around.

In these cases where you have to do priming or painting on the surface of the fiberglass, sanding is necessary. Sanding will prepare the surface for appropriate painting or priming. Sanding will make the surface of the fiberglass more abrasive. Paint or primers adhere to the abrasive surfaces more strongly.

Place the fiberglass under the sun to cure:

There’s nothing like a good old-fashioned sun tan to show your summer glory. But before you head outside, make sure to sand down your fiberglass with the right grit. This will result in a stronger and more durable product that will look great year-round.

Make sure to avoid hot spots while sanding, as this can result in uneven sanding and potentially a weaker product. When you’re done sanding, be sure to give the surface a final coat of fine grain grit to achieve the desired level of smoothness or sheen. Now go enjoy the great outdoors!

Things You’ll Need:

Sanding fiberglass is a necessary step in the finishing process. However, it’s important to do it the right way to avoid sanding the surface too harshly and ruining the material. Here are the things you’ll need to get started:

  1. Rinse off the area to be sanded with clean water and dry it thoroughly.
  2. Next, grab a bucket or container for sand and fill it up to the correct level.
  3. Apply enough pressure to smoothly remove the old surface – don’t scrub!
  4. Make sure your newly applied substrate is level by adjusting the levels of sand in your bucket or container.
  5. Select the appropriate grit sandpaper and begin Sanding.
  6. Be gentle when sanding fiberglass, as it can easily break!
  7. When finished, rinse off the area with clean water and dry it thoroughly before applying a sealant or paint.

Necessary Tools

When starting any job, the choosing of the tool is very important. The success of your work will depend on the correct selection of the tools. Sanding the fiberglass is no exception here.

If you do not choose the right tool, it will make the work difficult and stressful. Now, of course, you have to choose the tools in terms of your extent of work, your budget, the kind of results you are expecting, your workspace, and so on. Here, we will cover all the possible aspects you need to consider while choosing the right tool.

Right Sandpaper

If you choose to use your hand to do the whole sanding process, the choice of sandpaper is crucial. The coarseness of the sandpaper has an impact on the overall sanding process. Fiberglass is more sensitive than other materials where sanding is used, and so proper sanding paper is a must.

A higher grit of the sandpaper indicates that the coarseness will be less rough. Using this less rough sandpaper, you can get a smoother surface. You will need to switch between different sandpapers having different grits as you proceed in your sanding process.

Sandpapers With 80-100 Grits

When you are first starting your sanding process, sanding with sandpapers with 80-100 grit is ideal. It will help you to do the hard peeling off the surface of the fiberglass. This sanding will help you get out the extra marks on the surface.

Sandpapers With 100-120 Grits

This higher sandpaper will give you much finer sanding. When you remove the marks using the 80-100 grit, the sandpaper with 100-120 girth will be taking care of the smoothening process.

Sandpapers With 150-220 Grits

Using the sandpaper with 150-220 grits is your judgment call. It will be based on the amount of smoothing you require. Depending on your desirable smoothness, you may stop sanding using your earlier sandpaper or continue with 150-220 grits.

Grading Weight

You have to choose the weighted grade of the sandpaper before buying them. The weighted grade indicates durability. Generally, it is graded by the alphabets from A to E. Here, the A-graded sandpaper represents the less durable sandpaper, while the E-graded sandpaper indicates the most durability. You may choose between them depending on the extent of fiberglass surface you have.

Sander Tools

To get a smooth and shiny finishing with precision and accuracy, electric-driven sander tools can be used. While using sandpaper, the force of your hand will vary all along the process. It is really hard to apply the same amount of pressure all along the process. So, the sanding can be uneven. The power-driven tools will eliminate such problems. These electrically driven tools will give you the desired smooth finish all over the surface of the fiberglass.

Orbital Sander

Orbital sander is the most common type of sander you will find in the market. The sanding technique requires an orbit action. It means the action of the blades will be circular. You will get a plain ending at the edges than many other electric sanders. It is generally applied over metals, wood, and plastic. But you can use it ideally for fiberglass. For your balanced durability, it has a speed adjuster.

Detail Sander

Detail sander is very useful in the case of edges of the fiberglass surface. It is smaller in size and is very suitable for reaching and working in the right places, including the surface edges. Remember, curve places can be of two types. One is convex-shaped, and another is concave-shaped. There are some materials which are going to help you to stand at curved places.

Angle Grinder

Angle grinders are generally used to remove various adhesive substances or grind something on the surface. But it can also be applied for sanding. Now, you have to respect the power of such a tool while sanding. You can use it to reach the curved areas of the surface. Holding the grinder at the Right Angle is the key. Be careful not to push using it too hard on the surface; otherwise, it can damage the surface of the fiberglass.

Tailed Sanding Apprentice

It is a very small tool that can be held by the fingers of your hand, just like a pencil. It can be used to reach many delicate areas of the surface of the fiberglass. It is especially helpful for concave surfaces because it has a very flexible maneuvering capacity.

Cylindrical Metal And Sponge

To get to every part of the curved surface, especially for concave surfaces, the use of a sponge with a cylindrical-shaped metal can be useful. In this case, first, you have to attach your sandpaper to the sponge and then attach the sponge to the metal piece. Now, sanding a concave surface will be easier for you.

Drill and Sanding Drums

The combination of a drill head with sanding drums can assist you in working on curved surfaces. By attaching the sanding drums to the head of the drill machine, you can work your way through the surface. The sanding drums are made out of rubber and therefore are very flexible. This flexibility really helps in working around the curved surface of the fiberglass.

Dual Action Sander

Dual-action sander is an excellent choice as a sanding tool for sanding the surface of the fiberglass. If you ask any expert on which tool to choose for sanding, they will most probably recommend you this particular tool. It is a powerful tool with a long-lasting guarantee. It is also easy to use with the hands as it is lightweight. The crucial advantage of it is that it can control the amount of dust produced while sanding.

Usually, the sanding process produces a lot of dust. It is actually a challenge for anyone who is sanding to control this type of dust. It does not require you to use much energy while using it. It gives you faster results than other sanding tools. As it is lightweight, you can smoothly use it with your hands. All types of surfaces, including the rough and the smooth surfaces, can be sanded using dual action sander.

It is also budget efficient, and you may choose between a variety of sanders according to your budget and other convenience.

Belt Sander

As an alternative to other sanding tools, this belt sander can be used. Belt sanders are ideally used for sanding the wood surface. But it is also helpful in sanding the fiberglass. It may not give you all the advantages that other tools provide, but you can still get a smooth finish.

Blocks For Sanding

As you can imagine, sanding can be a laborious job. The work becomes a little more difficult when the coarse sandpaper becomes uncomfortable to handle. Also, sanding with mare hands will drain a lot of energy because it is not ideal for gripping and doing the work.

You are happy to get sanding blocks. Sanding blocks will help you get a better grip on the sanding paper. So, the sanding job will be a lot less stressful. Getting a proper grip will also help you conserve energy and be easy for your own body.

Abrasive Sponge

Abrasive sponges are the common sponges that you can find for washing different types of dishes. It can be useful in sanding fiberglass. Firstly, it will help you clean the whole fiberglass before starting your sanding as part of the prepping process. These sponges will be flexible enough to mend with the shape of the surface and help you clean the edges.

Grease And Wax Remover

Removing the grease, wax, or any type of foreign substance on the fiberglass surface before starting the sanding process is necessary. For this, you may use any kind of grease or wax remover. You may apply them with the help of any cloth or rugby, just sweeping them off.

Vacuum Cleaner

One of the preventive measures before starting the sanding is getting a vacuum cleaner. For the sanding process, a required amount of dust will be generated. To get rid of them instantly, you can very well consider yourself keeping a vacuum cleaner beside you. Thus, the dust will not interfere with your work.



Besides a vacuum, you might also consider keeping a bucket nearby. After collecting the dust with the help of your vacuum cleaner, you can dispose of the dust in the nearby bucket. It will minimize your effort in getting the dust to your dustbin. Also, the dust of the fiberglass can be utilized for other purposes. You can keep the bucket to store the dust for future use.



The dust of the fiberglass will not be adjustable to your skin. It will be the opposite. It can irritate your skin. Besides, working with dust on your hands will not be very convenient. So, all matters considered, it is better to wear gloves before starting working.



The dust produced in the process flies and can enter your eyes. It will be impossible to work with dust flying inside your eyes. It will also not be very good for your eyes. So, you must wear goggles which cover all of your eyes and leave no room for the dust to enter.



Wearing some sort of respirator is also important in sanding fiberglass. The produced dust can get into your respiratory system and cause trouble. Your respiratory system can be blocked if an excess amount of dust enters your body.

If you have asthma and some sort of allergies, you may need to be taken to the emergency room. So, while working, be sure to wear some sort of respirator to protect yourself from such hazards.

Other Precautions

Besides ensuring you wear gloves, goggles, and respirators, you should also ensure the room is well ventilated. Doing it inside the house needs to make sure to keep it at the doors and windows. If you are doing it outside, make sure your children and pets do not come too near the working area, or they might face health hazards. Choose an empty place near you. You can also keep a first aid box near.

The sanding process involves sanding with sandpaper which can cause cuts and bruises. If you are using power tools, it can also cause accidents. So, keeping a first aid box ready and within your reach will be a smart thing to do.

Sanding Process

Now that you know the necessary tools and precautions, let us dig into how you can complete your sanding process.



Curing is an underrated step to do before sanding. It is a very necessary step in sanding the fiberglass. It will ease the sanding process. You can complete the sanding much faster if you first cure the whole fiberglass body. Curing helps to remove the air from the air pockets created by the gel coats.

Gel-coats are used in the body of fiberglass. These gel coats can create air pockets and store air in them. This is not desirable at all. To cure the fiberglass, you need to place it in the sun. Keep at a place where it can get direct sunlight. Keep it like for 5 to 6 days and give it a good assemble.

Assemble The Parts

Keep it like for 5 to 6 days and give it a good assemble. It is going to help you perform on the top of the fiber graciously. You can save time through this process. It is more applicable if you are working on big surfaces to sand with.

Working on cars, boats, bathtubs, etc., may involve many parts. So, assemble or join all the parts together first, and then start working on your sanding.

Using The Grease Or Wax Remover

Your fiberglass may deposit grease over some time of use. If your fiberglass is used in cars, then it is maybe subjected to much grease and dirt. Also, if used as furniture and other household materials, it can accumulate grease, oil, wax due to constant use and touching. Before sanding, you will want to remove all the grease, oil, and wax.

Take a piece of cloth or rug. Soak it with grease or wax remover. You can get grease and wax remover from most of the stores. Just rub the surface of the fiberglass with it. You will have to rub the surface again with a clean cloth this time. Now, wait for it to dry for a specific time before starting to work again on your fiberglass.



After you have cleaned the surface of your fiberglass thoroughly, you can start sanding now. As mentioned earlier, you will start sanding with the sandpaper having lower girt. It is wise to start with 80-100 grit.

Approach the sanding slowly. Do not put much pressure on your hand, or you will risk damaging the fiberglass. You might desire to do it in a cross manner. Starting from the top right area of the body and working for the car. After finishing this, the start may be from the top left corner and way back to the below right corner. Try to finish up the work with equal amounts of strokes to get the most even look.

After going for the first time, wait for a bit. This will allow the putty to cure. It is best to do this work in the sun because the curing process will be much more appropriate and faster. Now, to begin the second round of sanding, increase the girth of the sandpaper. You may now try sandpaper having the gift of 100-120. This will provide finer sanding.

The surface will be smoother. As usual, starting to do it slowly and smoothly will prevent you from getting damaged. After sanding it with 100-120 girt, you may find your surface perfect according to your requirements. But sometimes, the mentioned girt does not give the ultimate results. In this case, you may simply increase the girth of the sandpaper up to 100-120 girth.

This higher girth will provide you with more smoothness on the surface of your fiberglass. Be sure of the wastage of the glossy layers. If all glossy layers are not removed, you cannot continue other works on the fiberglass surface. The new priming or painting will be uneven and come up with spots. Before moving on to higher girths, be sure the new girth value is suitable for your fiberglass and will give the result you are expecting.

If you are sanding with any type of power tool, be sure you are well familiar with the tool and the extent it can sand. If you are not sure, you can try on another unusable fiberglass just to understand how much power you need. If your power tool has the option to increase or decrease the power, find out which power level will be suitable for your fiberglass.

The angle at which the machine is held can also be crucial. So, get to know the proper angle for the particular power tool. Do not dig deep with the machine, or it will ruin your fiberglass.

Sanding With Hand Or Power Tools; Which Is Better?

Sanding with hands with the help of sandpaper is a better choice than sanding with power tools. Though sanding with the help of power tools will be less time-consuming and more laborious, it sometimes will not give you the best result.

Sanding with power tools will expose you to the risk of overdoing the sanding and reaching the fibers all the way. It is a less controlled process. On the other hand, sanding with the help of your hand is more controllable. So, forgetting the more desired result, sanding by hand with the help of sanding paper is the best option.

If your sanding does not result in perfect smoothness, do not worry. It would be, in fact, advantageous for you if the surface remains a bit abrasive.  Planning to paint fiberglass later on, will help to adhere to the surface area. After sanding is done, make sure to remove the dust for the sanding. You do not want to paint or prime over the surface, which is already covered in dust.

Filling The Imperfections

While working with your hands on the surface of the fiberglass, you may accidentally use more force than necessary in certain places. Do not get disheartened. It is quicker than you can imagine. It is more common than you can imagine. You are bound to have this issue while sanding fiberglass.

To correct this mistake, you have to fill the spots which are too deeply sanded. You can fill those using glazing putty. It will create a seal on the surface of the hole. So, if you now apply paint or primer, the uneven surface will not cause a problem.

Cure It Again

After getting your sanding work done, it is best to get it under the sun to cure it again. If you already did the work under the sun outside of your house, then you do not have to wait for long. But, if you did the work indoors, keep it in the sun again for curing for the second time.

Do Not Wait Up!

For getting the best result, do not wait up. You have to apply your primer or paint just after sanding to get the best results. Before that, you, of course, have to clean it and let it dry. But do not let it stay; however, it is overnight before starting work again. Soon after it is dried from the washing, start applying the primer or paint.

Sand The Surface For Finishing

After you have applied the primer, sand the fiberglass again. Before starting sanding again, let the primer or paint set. Depending on the surface area and the primer used, the extent of the setting time would be different. You can do this using sandpaper of 180 or 220-grit.

Apply your primer again accordingly to get the desired result. If you want to apply primer further, sand the surface once more. Be careful of the sanding over the surface having a primer because it may ruin the use of the primer. Also, give the primer time to set on the surface of the fiberglass.


Sanding fiberglass can be a stressful job. It can also be a little bit tricky. But, do not get discouraged before even starting. It is possible to finish the work by myself. I hope now you know how to sand fiberglass. Just follow the tips and instructions mentioned here and get your job done all by yourself.

After reading this blog, you will know how to sand fiberglass safely and effectively. You will also know the things you’ll need and the best way to clean your work area. Finally, you will be able to place fiberglass under the sun to cure it.

Frequently Asked Questions

1.What Is Sanding Fiberglass?

Ans. Sanding fiberglass is a process of removing the outer surface of the fiberglass using sandpaper. By doing this, you achieve a smoother finish on the boat that will resist water and wear better over time.

2.What Are Some Tips For Working With Fiberglass That Will Help Me Avoid Accidents?

Ans. Some tips for working with fiberglass that will help you avoid accidents are to wear a face shield, use extreme caution when handling the fiberglass resin, use proper safety equipment, and stay alert. The source of this information is the Fiberglass Safety Institute.

3.How Do I Sand Fiberglass?

Ans. The process of sanding fiberglass is to use a grit size that will remove the coat of resin and leave the fiberglass with a smooth finish. First, use a cloth to clean the surface of the fiberglass. Second, apply a liberal amount of sanding cream to the surface of the fiberglass and work into the crevices using circular motions. Finally, buff off any excess sanding cream with a pad or microfiber cloth.

4.What Is The Difference Between Sandpaper And Fiberglass Sander?

Ans. Sandpaper is made of sandpaper cloth which is a paper-like material with grit on one or both sides. The grit is the number of grooves that run along the length of the sandpaper. Also, fiberglass sanding sheets are made of fiberglass cloth and have grit on one side only.

Leave a Comment