How To Sand Fibreglass

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Sanding your fibreglass component gives it a smooth feel that’s easier to prime and paint.

In this guide, I will show you how to properly sand fibreglass.

Being a DIY enthusiast, I enjoy getting my hands dirty.

I recently had a tough time sanding my car’s body.

After agonizing and researching, I finally learnt how to do it. So I thought I’d share the solution with you.

What Items do you require?

Before I begin, here are a few things you require for your sanding job:

  • Sandpaper
  • Glazing putty
  • An orbital sander
  • Hand sanding block
  • Grease remover
  • Gloves, safety goggles and a respirator

First off, I need to insist that you sand with caution.

The fibreglass dust might make your skin itchy, or worse, get into your eyes and nose. Ensure you always wear your safety kit.

With that said, let’s dive into the steps.

Step 1: Cure under the Sun

Place the fibreglass under the sun for 5 to 6 days. New fibreglass has Gelcoat on the surface.

Curing it under the sun allows any trapped air to escape from the Gelcoat.

This step will ease your sanding process.

Step 2: Assemble all the Necessary Parts

Before you begin the sanding process, assemble all the fibreglass components that you want to sand.

This step is helpful if you are sanding different parts in a larger body, such as a boat or a car. Assembling them will enable you to sand consistently without spending too much time smoothening the edges.

Step 3: Clean the Fibreglass body with Grease Remover

Before sanding, you need to clean the fibreglass body with a grease remover. Cleaning it removes surface contaminants such as dirt, silicone, grease and oils. It’s best to get rid of these contaminants because they might affect your paint job.

Step 4: Begin Sanding with a Coarse-grit Sandpaper

It’s now time to begin the sanding process. Start with 80 or 100 grits sandpaper to remove the rough patches, then work your way up, depending on how smooth you want the surface to be.

The higher the sandpaper grit, the smoother the surface

Step 5: Fill up Uneven spots with Glazing Putty

Use glazing putty to fill up low or uneven spots. You can proceed to sand again once the glazing putty dries off.

Step 6: Apply Primer

Spray primer once you are done sanding. Primer helps bond the sanded surface together. It as well helps adhere paint to the surface.

Step 7: Finish with a Fine-grit Sandpaper

Finish your sanding job with a fine-grit sandpaper. A 180 to 220 grit will do. Leave the sanded body under the sun for a while, then apply your desired paint.

Conclusion: How to Sand Fibreglass

Great, you are now ready to sand it yourself. For a quick recap, start by curing under the sun, assemble all the required parts then clean with a grease remover.

Begin sanding with coarse-grit sandpaper, apply primer, then finish with a fine-grit sandpaper.

Lastly, remember to wear your gloves, goggles and respirator for safety purposes.