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Wet sanding is one of the best methods to remove minor scratches from metal, wood, and plastic surfaces. While we’ve previously discussed sanding techniques for metals and wood, we’ll tell you how you can wet sand plastic in this article.
In a step-by-step guide, we’ll also explain sandpaper grits for wet sanding and the whole process.
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What is grit?
For beginners, the grit of sandpaper is the number of abrasive particles attached to the paper. The higher the grit, the smaller the particles and finer are the scratches left behind.
You get sandpaper varying from 200 to 3000 grits. Based on the project, you may need different grits to make sanding easier.
Now, let’s move back to wet sanding. Don’t know what that is?
Here’s a quick guide to wet sanding.
How Wet Sanding Works?
Wet sanding uses water or any lubrication that helps wash away the grit particles, dust, or other blemishes during the sanding process. Wet sanding can be done through sandpaper wrapped around sanding blocks or machines (usually electric sanders).
In wet sanding, the sandpaper is soaked with water or the available liquid solution to reduce friction before sanding. During the sanding process we recommend that you use a spray bottle to spray liquid on the surface to keep both the surface and sandpaper moist.
Additionally, it would be best if water and a little detergent were used in mixture form, so it lowers the surface tension of the water and helps the sandpaper and material to wet thoroughly.
Why Wet Sand Plastic?
As we’ve outlined before, sanding is one of the effective methods to remove scratches from the plastic surface. But it’s important to understand the reason that we recommend the wet sand technique for plastic vs. the typical dry sand technique you would use on other types of surfaces.
When you rub sandpaper on plastic, it creates friction. Now, it’s common knowledge that friction creates heat. Unlike wood or metal, plastic does not reflect heat. Therefore, even the slightest heat can soften, crinkle, or damage the plastic, which can ruin your project.
Of course without sanding, the plastic surface remains uneven and that’s the whole point of sanding a surface. Therefore, wet sanding is the best method to provide the plastic with a glossy and smooth finish.
Pros & Cons of Wet Sanding Plastic
Increases surface area of plastic
Sanding increases the surface area, allowing more paint and other sealant layers to adhere to the plastic. This is especially important if you want to add multiple coatings to the plastic. Gentle scuffing can also improve adhesion by doubling the surface area.
It makes plastic look impeccable
There’s no denying that sanding gives projects a refined finish. The surface becomes smooth and appears very glossy without any scratches.
So, we listed the benefits but what about the cons?
Here are some downfalls of sanding plastic.
Gentle sanding can work wonders on plastics, but excess pressure can cause blemishes. The plastic splits off into hair-like strands, and this defect is called hairing. This process is also called thermoplastic reflow, scratching, or blemishing.
Other than this, there’s only one major drawback of sanding plastic. The heat caused due to friction can damage the plastic. For this reason, using a gentle motion, or a light touch with an electric sander, when sanding a fragile material like plastic is always recommended.
How to Wet Sand Plastic? Step-By-Step Guide & Tips
1. Gather your tools
The tools or objects you need while wet sanding the plastic are: sandpapers with suitable grits.
- Depending on your needs and object roughness, you can start with lower grit sandpaper, such as 200-grit.
- The higher grit sandpaper can be 400, 500, 600, 800, or even 1200-grit if needed, depending on your desired outcome.
- A container for water, detergent mixture (or any other wet sanding lubricants).
- A cloth to remove dust or debris.
- And finally, your plastic object.
2. Get your Plastic Object ready
Clean the object you will be working on. Clean it with a mixture of water and detergent. You can also use a water and vinegar solution to clean off dirt and grime.
Put the object on a flat surface to ensure it does not move while working. If possible, mount your plastic sheet, so it doesn’t move during sanding.
3. Wrap your Sandpaper around the Sanding Block
Next, you need to hold the sandpaper in a position so it won’t move by itself and ruin the object. Even though you can still use the sandpaper directly, the sanding block makes it even more comfortable.
How do sand blocks work? You wrap your sandpaper around the block. The block can be made of wood or cork that helps hold the paper through its smooth flat sides.
4. Soak your Sanding Paper with Liquid
Different lubricants are available in the market that you can use for wet sanding: silicon-based, mineral oils, or synthetic hydrocarbons. They are considered the best lubrication for plastic during wet sanding.
However, we use a water and detergent mixture for lubrication as they are more efficient and cost-effective. So, we’d recommend you use the same.
Before wet sanding, dip your sandpaper block in the water solution to let it absorb the liquid solution (soak it for 2-4 hours).
You will still need to lubricate the sandpaper while working. For this purpose, we use a spray bottle to sprinkle lubricants on the object during the sanding process. Start sanding with dry sandpaper (1-2 passes), then move on to wet sanding.
5. Start Wet Sanding
Usually, we start with 400-grit and 600-grit sandpaper, as plastic material is not as rough as metal. But, again, it depends on your plastic material and its condition (rough or smooth). If your plastic sheet has the deepest scratches, start with 80-grit sandpaper.
Do sanding in the direction of the scratches or circular motion. If you’re not using a sanding block, the best practice is to use your palm to grab the sandpaper and sand the surface.
Next, move on to 200-400 grit sandpaper after a few passes, and keep switching to higher grits until you achieve your results. Usually, we end up on 800, 1200, and 1500-grit sandpaper.
6. Check your Sanding results
After sanding, you can check your progress using a microfiber cloth to wipe the surface area and see if your desired result has been achieved.
You can also check the sanding results using your fingers. It works like rubbing your finger on your plastic object to check for any roughness or rough spot on the object. If there are any, switch to higher grit sandpaper and continue sanding, until you get rid of that roughness.
7. Final touch
If you get your results, this is great. If not, you can switch to higher grit sanding paper (1200-grit or 1500-grit) for final finishing. And lastly, to get shining results, you can use polishing agents on your plastic object.
Can You Wet Sand Plastic With an Electric Sander?
You can use an orbital sander for wet sanding plastic surfaces and we would recommend a dual-action model. There are a variety of water-resistant sanders available on the market, commonly referred to as water bug sanders. However, we use a regular dual-action sander for wet sanding, and we never faced any issues, as we only dip pads in the water, not the whole sanding disc.
When it comes to hand sanding, we recommend using a sanding block if you’re dealing with a small surface area. However, if you’re working with larger surfaces that require significant effort, we suggest using an electric sander instead.
Are there any alternatives to wet sanding plastic?
You can use toothpaste, baking soda, heat guns, or polish to remove minor scratches in plastic as follows:
- Use a small amount of toothpaste or baking soda on a damp cloth, wipe it in circular strokes on the scratched surface, take a clean damp cloth to remove the residue, and a clean dry cloth to dry the surface.
- Use a simple hair dryer or heat gun, set it on the lowest heat settings, and direct the heat towards the scratch for 5-10 minutes, and the small defects on the surface will disappear.
- Use standard car polish or brass polish, apply a small amount on the scratched area with a damp cloth, buff the surface with a lint-free cloth, and remove any excess polish; avoid rinsing with water.
These techniques are widely used in households to deal with blemishes on surfaces like cars and marble countertops. Remember, these are useful for small dents and scratches only. For deeper, more protruding scratches, wet sanding is still the best way to go.
Which plastic materials can I wet sand?
You can wet sand materials, such as ABS, polycarbonate, acrylic, and fiberglass. But make sure to practice on a tiny area on the surface before proceeding with wet sanding. This will ensure that you don’t cause any damage to the plastic material.
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