Sanding plastics is a common task in the manufacturing process. It’s done to remove imperfections, improve the surface of plastic products and reduce costs. Wet sanding is one of many types that can be used on this material. Here are some tips on how to wet sand plastic for your next project!
You can sand plastic.
Sanding is a great way to smooth and shape the surface of any material, including plastic. You can use various types of sanders and sandpapers depending on the type of finish you are looking for.
When sanding plastic materials, it's essential to take your time not to overheat or melt the material. Make sure to wear eye protection when using power tools.
Start with medium-grit (240) paper, then move up in grits from there as needed until you have achieved your desired smoothness level.
Should You Sand Plastic?
Sanding is an essential step for glossy plastic before you paint so that the finish will not be abrasive. Wet sanding should come by you before painting on lighter surfaces. When you wet sanding plastic, the surface area will increase to more coats to stick.
"Now, the question is, do you smooth a plastic surface by using wet sanding? It isn't very easy to sand plastic, but it mustn't be underestimated. Most issues you will face will be heat-related when sanding plastic."
The use of sandpaper generates friction. Now, it's well known that friction causes heat. Plastic does not absorb heat. Beware of even the slightest amount of heat, as it can hurt, soften, or wrinkle the plastic. If you are not very careful, this could destroy your project. Be careful not to avoid excessive friction when sanding plastic, which could melt the plastic. When using an electric sander on plastic, this is particularly critical.
Sanding the plastic surface doesn't take the roughness out completely, though. On the other hand, you can easily get perfect finishing for plastic surface by wet sanding plastic smooth. Instead of wasting time figuring out whether you can sand plastic, you can look at the next section below.
7 Things Keep in Mind when Sanding Plastics
When working with plastic, sanding is sometimes necessary to smooth the finished piece and remove any rough tool marks. Sanding can be tedious, but it must be done carefully because even a slight slip can mar the surface or dull your edge tools. Here are seven things you should know about sanding plastic:
1) Using Sandpaper Grit Marks
There's an easy way to determine which grit of sandpaper to start with when sanding plastics: look at the mark left by the previous grit. This mark is called a "transfer" and will tell you what you need to know. For example, if the previous grit left a faint scratch pattern behind, use either 320-grit or 400-grit paper for the first step. If the scratch pattern is more pronounced, use 500-grit or higher for your first sanding pass.
2) Polymerization Shrinkage
Sanded plastic tends to shrink when it dries, leading to cracking and warping. The good news is that these problems are easily prevented by applying a thin coat of spray-on varnish (polyurethane works well) immediately after you finish sanding. Test the thickness of your coat in an inconspicuous place; if it's too thick, apply another light coat using the same method until you get it right. Allow the varnish to dry overnight before handling the piece.
3) Sanding Small Details
You can use regular sandpaper for small details, but it tends to clog up and tear. A better approach is to cut strips of 280-grit wet dry sandpaper (available at most hardware stores) into inch-long pieces. Just dampen the strip with water and fold it in half; then press it firmly onto your work surface while rubbing the plastic with your fingers. This method is especially good for finishing rounded parts because the paper conforms naturally to its shape, resulting in a smooth finish.
4) Sanding Curved Surfaces
Curves and compound angles are difficult to sand because you can't keep the grit flat against the surface; this results in circular marks that are difficult to remove. The best way to sand these areas is with a sanding sponge. These sponges are stamped out of various aluminum oxide grits (just like sandpaper), but they hold their shape much better than regular sandpaper because the backing material contains an adhesive. You can also use them dry or apply masking tape over them before using them on your workpiece.
5) Sanding Inside Holes
Thin plastic tubing makes great gun barrels in models, but you need to sand the end flat before attaching it to the model's body; otherwise, you'll see a bump where one tube connects to another. A simple way for this task is to cut off a small section of a sanding sponge, cut a shallow groove with a hobby knife, and slip the tubing into the groove. Now you can sand away without fear of damaging the tube's wall.
6) Fine Grits for Fins
Most fins on airplane models are too small to be adequately sanded with 320-grit paper, even if they're made from sheet plastic. So instead, you can make these fins smooth by first sanding them with 400 or 600-grit paper and then going over them with 1000, 2000, or 3000-grit paper. This technique is especially helpful when you need to construct complex shapes out of multiple plastic sheets. A similar work well for sculpting clay is called "blending."
7) A Shot of Spray Paint
Spray-paint adheres to plastic like a magnet, so you should always prime it before applying the finish coat. The simplest way to do this is to use an aerosol can of Krylon primer (available at most craft and art supply stores); just spray the inside surfaces of your model, let them dry for five minutes, and then spray two light coats of whatever color you want on the outside.
Sanding Tools for Plastic
- Sanding Sponge
- Fine Grit Sandpaper
- Foam Sanding Pad
- Dish Washing Detergent
- A rag
Wet Sanding Plastic (7 Easy Steps)
Step-1: Wash the plastic
Use a lint-free cloth to clean the plastic while you wet sanding. If required, use a degreaser to remove all dirt, grime, grease, and grease stains. Cleanliness is the must-to-guaranteed requirement for any effective painting. A degreaser is essential. It's best to make the surface as smooth as possible while sanding.
Adding a few drops of dishwashing detergent to the water is enough to remove any greasy residue. If you have another container of water, fill it and set it aside.
Step-2: Use wet/dry sandpaper to the sanding pad
People who just need to sand one or two surfaces need not follow this step. Get foam sanding pads for plastic smoothens. Select the sandpaper grit that best corresponds to the finish of the surface. Submerge the end into the bucket or wet the sandpaper by using the sprayer.
Related: How to Use Wet Sandpaper? [Know 7 Easy Steps from an Expert]
Step-3: Sand in a circular motion
With a light hand, softly work on the sections in a circular motion. Make the circles as large as possible. Be sure to frequently pick up and dust off the excess plastic build-up on sandpaper regularly. The way you sand it should be random. You need to spray water often on paper and plastic.
Related: Don’t Make These 23 Biggest Mistakes When Sanding
Step-4: Switch to higher grit sandpaper
Using 500-grit sandpaper, you must wet sand the whole surface. Then move to the greater number grit-paper for more smoothness.
This is where you can use a finer grit paper in the same manner. Although try to use small, gentle strokes for even coverage, remember to wet the paper from time to time. Finally, do not let the paper or plastic dry out completely; using the lightest of touches, go around in a random motion.
Step-5: Inspecting the sanded plastic
Using a damp cloth, clean the entire surface, then repeat on a dry towel to remove any particles that remain. Look closely for nooks and crannies for finding roughness and scratches. If you are looking for scratches in the plastic, use your fingers. The aim here is to smooth as much surface as possible.
Once the scratch removes, you can proceed to the next level.
Step-6: Use fine grit sandpaper for Final Touch
Don't add any pressure and take fine sandpaper to the floor. Please do it again with additional 800-grit sandpaper by placing the sandpaper on the foam sanding pad. Then soak it, and run through the plastic one more time. You should wet sand plastic in random circles that randomly overlap each other for getting the best result. To avoid observable patterns, rotate the paper often and keep the paper moist. Your plastic has been ground down to the same smoothness as glass.
Related: 44 Creative Sanding Tips You Need to Know
Step-7: Clean the area and remove dust
Wash off the plastic. If you allow it to dry thoroughly, it should be glass-smooth. Then clean the dust carefully with the help of a vacuum cleaner.
Here is a video showing how to wet plastic sand:
Which is the best kind of sandpaper to use on plastic?
The kind of sandpaper you'll want to use, whether wet or dry, is called silicon carbide, and it is the best-wet sanding paper for plastic trim.
Often, it's black or gray. You have to wet the paper and sand in a spiral fashion. To prevent scratches on the surface, don't sand in a typical pattern.
Firstly, you have to start with 220-grit sandpaper to get lightly sand all over the surface.
If the size of the sandpaper increases, the finer the sandpaper you will get. Usually, for plastic, from 240 to 360 grit-paper is extremely rough. You can need to up the grit number after that. Smoothness needs different grit sandpaper depending on the surface texture and work rate you are trying to achieve.
You will have a smooth finish if your sandpaper progresses from 400 to 800 grit-size. If you want a mirror-like finish, work hard at getting it. Finishing the final touch before painting in wet sanding requires sandpaper ranging in 800, 1000, and then up to 5,000 grit numbers.
Benefits of Sanding Plastic
A gentle sanding can give fantastic results on plastics, so try to use light and gentle pressure. Don't try to do wet sanding plastic fast.
You can repair polycarbonate and acrylic plastics with wet sanding. Many plastic materials scratch easily, so be careful when wet sanding automotive plastic. For doing this accurately, use fine-grit sandpaper. The optimum approach is to start wet sanding at 220-grit and finish at the finer paper until you are satisfied with the appearance.