Restoring hard plastics can be a menace especially if you don’t know what to do. Thankfully for you, we know just what you need.
First, throw away those coarse sandpaper grits. The best way to go when restoring plastic is wet sanding. This requires a higher grit.
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.
What is wet sanding?
There are two types of sanding–dry and wet. Both follow a different approach and are suitable for different surfaces. When you sand plastic, the ideal technique to use is wet sanding.
Wet sanding is a technique widely used on car paint jobs and even 3D prints to give them a mirror-smooth finish. It is typically done after dry sanding a surface to get an even finish. Unlike dry sanding, wet sanding removes scratches from the surface.
When done correctly, wet sanding levels out any abnormalities left during dry sanding. The scratches continue to shrink until finally, the surface reflects flawlessly.
Water or some liquid is used as lubrication to carry away grit particles stuck on the surface after you dry sand it. In most cases, water with a little detergent is used for this process. The detergent reduces the surface tension of the water which is great to wet the material thoroughly.
For a better finish, we recommend soaking the sandpaper in the liquid overnight. This ensures it does not absorb moisture during the sanding process.
How To Wet Sand Plastic?
Washing the Surface
Wash the plastic that needs to be sanded. Remove all the dirt, grime, and grease from the surface. If required use a de-greaser. The cleaner the surface is before sanding the better.
If you don’t have a degreaser, simply add a few drops of dishwashing detergent in water. Fill another bucket of water or a spray bottle if available and set aside.
Attaching sandpaper to the sanding pad
People who need to sand just one surface and aren’t expecting any more sanding projects can skip this step.
Get a foam sanding pad. Adhere a sanding paper of your grit preference to the pad. Dip it into the bucket or spray water on the paper and the surface.
Sanding in a circular motion
With a very light hand, sand the surface in slow circular motions. Keep changing the size of circles to cover maximum areas. Make sure you clean plastic build-up and re-wet the sandpaper occasionally.
Switching to a higher grit sandpaper
Let’s say you’ve sanded the entire surface with a 500-grit paper. Once you are done with it, switch to a 700-grit paper.
Repeat the previous step with the higher grit sandpaper. Use gentle circular strokes varying in size and make sure you wet the paper from time to time.
Inspecting the sanded surface
With a damp rag, wipe the complete surface to remove any debris or dust. Look closely for spots that aren’t fully sanded. Use your fingers to feel any rough spots on the surface. The aim here is to ensure the surface is as smooth as possible.
Once you’re sure there aren’t any prominent scratches on the plastic, you can move on to the next step.
Take smoother grit sandpaper and sand the surface without applying much pressure. Move-in circles and use an overlapping pattern to ensure a smooth finish.
Always keep the paper wet and create a random circular motion to avoid a discernible sanding pattern.
Wash the plastic and pat dry the surface. After drying it should be as smooth as glass.
Should you sand plastic?
Sanding plastic is tricky but it shouldn’t be overlooked. You will face many problems when sanding plastic majority of which will be heat-related.
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. Even the smallest amount of heat can soften, crinkle, or damage the plastic. This can prove disastrous for your project.
However, without sanding, the surface remains uneven. To provide the product with an overall glossy and smooth finish, sanding becomes necessary. To help you decide whether or not you should sand plastic, we have weighed the pros and cons of it in the next section.
Advantages of sanding plastic
Increases surface area of plastic.
Sanding plastic increases surface area allowing more layers to adhere to the plastic. This is especially important if you want to add coatings to the plastic. Gentle scuffing can improve adhesion by doubling the surface area.
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?
Don’t worry, we’ve covered it all. Here are some downfalls of sanding plastic.
A gentle sanding can work wonders on plastics but if you apply excess pressure, it 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, it is always recommended to use a gentle hand when sanding a fragile material like plastic.
Tips to remove mild scratches from plastic
If you’re not a big fan of sanding, some techniques get rid of minor scratches from a plastic surface. 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, sanding is the best way to go.
Using toothpaste on minor scratches
Take a clean, damp cloth and dip it in some soapy water (lukewarm). Run this cloth on the scratched area in gentle circular motions. Dry the area with a dry cloth now.
Apply very little toothpaste (just enough to cover the scratch) to a damp cloth. Wipe it in circular strokes on the scratched surface. Continue rubbing it in circles for a while. Take a fresh damp cloth to remove any residue and the excess paste. Clean the area with another cloth to dry it down.
You can use this same method using baking soda instead of toothpaste. Combine equal amounts of water and baking soda to create a paste. Then follow the same process but use this mixture instead of toothpaste.
Using hairdryer for defects
Defects on smooth plastic surfaces can be concealed using heat. For this, use a simple hair dryer or heat gun.
Set the appliance you’re using to the minimal settings and direct the heat towards the scratch. Wait for 10-15 minutes and then polish the surface to render the scratches invisible.
If needed increase the temperature until the marks begin to diminish.
Car polish to smoothen plastic surfaces
Car polish can be used to restore plastic objects. Start by cleaning the surface with clean water. Remove any dirt from the affected area and apply the polish on it. Finish the job by buffing the surface with a lint-free cloth.
You can also use brass polish to remove fine scratches. Add a drop of polish on a cotton ball and rub it in the scratch. Use a clean cloth to remove any extra polish.
When using a polish remember to not rinse the plastic.