Sandpaper is one of the most common items you will find with professional painters along with all types of construction workers.
A simple product that combines sand or similar abrasive material on the strong backing paper, sandpaper is used to smooth surfaces, remove rust or paint, and can prepare a surface as well.
Sandpaper comes in different abrasive amounts called grit. The grit of the sandpaper may range from coarse and rough to nearly smooth.
Choosing the right grit for your needs will depend on the task at hand.
And that is what will certainly decide the success or the failure of your sanding task.
What follows are some tips that will help you identify the proper grit needed for sandpaper when you are planning to remove old paint and/or prepare surfaces to add new paint.
What Grit Sandpaper is Best for Paint Preparation?
When shopping for sandpaper always remember: Lower = Coarser
This simply means that the lower the grit number, the coarser the grains of sand or abrasive material will be.
Conversely, the higher the grit number, the finer the grits or grains of sand or abrasive material will be.
Although coarser sandpaper will remove more material from the surface, it will also leave deep scratches as well.
For proper paint preparation, you will want to choose a finer grit of sandpaper for the job.
While it may take a little longer with a finer grit, the results will be well worth the effort.
Sandpaper Grit Chart
| Grit | Type | Purpose |
|---|---|---|
| 30 to 36 | Extra Coarse | – Removing rust on rough metal – Sanding hardwood floor sanding |
| 40 to 80 | Coarse | – Removing the layers of debris – Removing the stock material quickly – Sanding the wood for varnish tough removal |
| 100 to 150 | Medium | – Prep and sand unfinished wood – Cleaning old and stains plaster from walls – Preparing wood for finishing and removing old stains/varnishes |
| 180 to 240 | Fine | – Removing the scratches, prepping unfinished wood – Light sanding between coats of paint on wood or drywall |
| 320 to 600 | Very fine | – Wood finishing or polishing – Light sanding between coats of finish – Sand metal and other hard surfaces lightly |
| 1200 to 2000 | Ultra-fine | – Final wood sanding – Polishing the thick finishes – Making the surface smooth and clear |
How Do You Know What Grit Sandpaper to Use?
While the above sandpaper grit chart seems to be self-explanatory if you are yet confused about what to use and when you can check our detailed guide.
Below are some of the recommendations on choosing the right grit sandpaper based on the task you are handling…
1- For Rough Finish
If you are working on something that requires rough finishing or if you need to remove the tough paint from the already painted surface like metal, you will need to use a coarser grade of sandpaper for getting the job done.
In most cases, this would be anything ranging from 30 to 80 grits based on your specific job and the surface you are working on.
If you desire to get a rougher surface as an end result you may be using near to 30 grits.
And for a slightly smoother surface use the macro grit grading near 80 grits.
In rare cases, you may also need to use extra coarse sandpaper (16 to 24 grit) where you may want to quicken the task.
This is like when initially sanding the hardwood flooring where you do not worry about the smoothness of the surface.
2- For Drywall Surface Prep
Minor issues with drywall or plaster may include small scratches or imperfections that can be easily covered by a coat of paint.
You will need to check the surface for any flaws and if you spot them, use medium-grit sandpaper such as 120 to scuff and smooth them out.
For fixing minor drywall issues, you can even use a 3M sanding sponge that works great in my opinion.
Such issues should be minor if you are sanding the surface. Otherwise, you will have to repair any larger defects first.
3- For Smooth Plaster and Drywall Repairs
Larger defects you find in most drywall include gouges, nail holes, cracks, and scratches.
You can use a common putty or spackle to fill in such defects.
Once it has dried, you can then use a fine grit of sandpaper to smooth out the surface.
120-grit is a common type of sandpaper used for such jobs.
Once you have completed smoothing the surface, you can paint it to further reduce any evidence that a repair was made.
4- For Sanding and Repainting Wood Surface
Wood surfaces such as baseboards can get pretty roughed up over time.
If you decide to repaint the wood surface, you can smooth it out using medium-grade sandpaper such as 120-grit.
Once you have gone over the surface, switch to a finer grade such as 180-grit, and go over the surface again.
The finer the sandpaper, the smoother the surface will be, so you can switch to an even higher micro grade if needed.
5- For Sanding to Prep Surface for Latex Paint
If you plan to put latex paint over oil paint, then you will need to rough the surface of the oil paint first.
This is because latex will need a rougher surface to make it stick. You can apply a coat of conversion primer.
Or you can use a fine grain of sandpaper such as 220-grit to rough the surface.
This will help ensure that it sticks properly while working on your do-it-yourself projects.
How Much Should You Sand the Surface?
Sanding the surface using sandpaper may seem to be an endless job, especially when you want to sand down the old painted surface for prepping and repainting.
The biggest challenge many of us will face is knowing how much to sand and when to stop.
Well, knowing how much to sand for getting the desired results and stopping when you have sanded enough, can only be achieved with experience.
However, for a DIYer, this can be checked by using two simple methods.
First Method:
After you have sanded for a while, remove the dust and look at the surface in a low-angle reflected light.
You can bring the sanded wood surface near a window or any other light source in your room to get this done.
Second Method:
Using a damp cloth or some water wet the sanded wood surface. And then look at the surface from different angles in the presence of light.
Both of these methods can help you check for the remaining imperfections, scratches, and flaws you need to remove.
Make sure that you use the right sandpaper grade according to your job and surface.
Also, switch between the grades as and when needed for getting the right smoothness and finish.
Does Sandpaper Make the Surface Smooth or Rough?
I would say BOTH.
Based on the grit count you are using your sandpaper can make the surface smooth or rough.
Like if you want to prep the surface for exterior painting where you want that the primer and paint to stick firmly, it would be better to use a lower count coarser sandpaper to make the surface rough.
But if you want to paint or varnish your interior furniture after using the filler, you will definitely want to get a nice smooth finish, and using a higher grit count would make the sense.
Considerations when Sanding
No matter what grade of sandpaper you are working with, it’s important that you protect yourself (using a proper particle mask) while sanding.
If there is a lot of dust involved, you should prevent it from spreading by sealing the doorways and closing off the vents in the room.
Also, remember that the paints done prior to 1978 may contain traces of lead. And sanding these types of painted surfaces can impose serious health issues.
If you are unsure about the presence of lead, it’s good to test the paint for lead before sanding.
How Does the Sandpaper Numbering System Actually Work?
Sandpaper grits can be classified based on the two popular numbering systems.
These are:
- CAMI: Coated Abrasives manufacturer’s Institute
- FEPA: Federation of European Producers Association
CAMI numbering system was approved by the American National Standards Institute and is the most common system used in the U.S.
FEPA on the other hand is used in Europe and a few other parts of the world.
You will often find these numbers labeled on the back of the sandpaper.
Remember, if there is a “P” included in the number (like P600) it’s a FEPA. And if there is none it is CAMI.
Other than these two most popular numbering systems there are other few systems (like “0” or “ought”, JIS for Japan) for grading grits of sandpaper.
However, these are rarely used.
The bottom line
So, which sandpaper to use for which project?
Sandpaper is commonly made with varied materials that come with varied chemical compositions.
They may contain natural minerals like garnet or synthetic ones such as alumina-zirconia or silicon carbide.
Plus, the backing of the paper may contain ingredients like cotton, polyester, rayon, rubber, paper, and a few others like mylar which is often found in very fine grits.
No matter if you want to get a shining well-varnished tabletop, a flawlessly painted wall, a smooth oak cabinet, or a finished hardwood floor without any imperfections; using the right sandpaper is important.
Especially when you want to prepare the surface for painting (for better adhesion of paint) it’s essential that you follow the right sanding procedure and tool with all the patience.
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Jack Luis is a semi-retired painter who loved painting his clients’ ideas on their walls.
He had worked as a painter for over a decade serving customers in areas such as Charleston, Mount Pleasant, Beaufort, and Georgetown, SC (South Carolina). Today in his free time, he likes to read and write about the newer techniques implemented in his profession. You may read more about him here or get in touch with him here.