Before you dip your paint brush into the bucket, you need to make sure you have a good surface to work with. And the most important step to achieve a smooth, long-lasting paint job is sanding. When and how to sand wood before painting, different ways to do it, and what happens if you skip this step – let’s dive into the finer details.
Why Sand Before Painting Wood
Wood in its natural state is rough and bumpy. Sanding is a process of abrading wood fibers to make them uniformly rough so that paints and stains adhere better and give a nice, smooth finish.
So, it’s important to give your wood a nice rub-down if you want the perfect finish. A few reasons to sand before staining or painting wood include:
- Fixes Imperfections: Sanding eliminates deep scratches, rough edges, and gouges in wood. Especially if you’re repainting old wood, sanding helps fix all its flawed and uneven parts so new paint will sit well.
- Opens Wood Fibers: The abrasive surface of sandpaper opens up the closed or previously sealed pores of wood. This makes it easier for paint or stains to penetrate the wood well and more easily.
- Aids Stronger Adhesion: Sanding roughens up the wooden surface so the paint, primer, or stain has something to “hold” or stick onto. This prevents peeling and chipping in the future.
- Picture-Perfect Finish: Sanding before and between coats of paint evens out all the bumps and brush strokes and gives a super smooth finish at the end.
- Refinishes After Chemical Stripping: One way to remove paint from wood is to use chemicals to strip off the old paint. This process isn’t as thorough and you still need to sand the surface before applying a fresh paint coat. Sanding after chemical stripping evens the surface and removes any leftover paint.
- Removes Mill Glaze: Mill glaze is the shiny look you get with new wood trim. If you don’t remove it before painting, the new paint won’t sit well. Sanding new wood gets rid of this glaze and creates a matte surface for a new coat.
Is Sanding Always Necessary?
Sanding is a crucial yet dusty part of the painting process in most cases, but there are times when it’s okay to skip this step.
Sanding is Necessary When:
- You’re repainting a wooden surface that was sealed with a top coat – a varnish, polyurethanes, or a sealant for example. Such finishes and sealers are generally glossy and don’t give much for the new paint to stick to. So sanding them is a must. If you skip sanding, the newly painted wood will peel and crack.
- Painting over old wood that has a lot of uneven parts like cracks and dents. You’ll also need a wood filler to fix these parts before sanding so it creates a strong base for paint.
- You’re skipping primer. It’s not always necessary to use primer, but to achieve a smooth finish over wood’s natural grain without a primer, you will need to sand it before applying paint.
- Old paint is bubbling, peeling, or cracking. Remove peeling paint with a scraper and patch with spackling. Once spackling has dried, sand the area until you get a smooth surface and repaint it.
Skip Sanding When:
- The old paint is still intact and in good condition. You just need to ensure that the surface is clean of grease, grime, and dust before painting.
- If the raw untreated wood is smooth enough and free from sheen, you can directly paint over it.
- The wood is even and you plan to prime it with a high-quality bonding primer. Such primers often state “no sanding necessary” and will adhere to most kinds of shiny surfaces.
- Doing minor touch-ups to your wooden structure. But it’s still better to partially sand the surface for better results.
Note: You can still sand these surfaces to improve adhesion. There is no downside to sanding.
Using Sanding Tools
There are three types of sanding tools, each used for a different purpose.
Power Sanders
Power sanders make the job quick, easy, and more efficient. The most versatile type of power tool is a random-orbit sander. Random-orbit sanders are an excellent power tool to smoothen wood evenly without leaving surface marks. If you’re shopping for one, we suggest getting a sander with variable speed and dust collection port.
Recommended Use: When sanding large pieces of wood, such as decks, floors, etc.
How it Works: Random-orbit sanders spin randomly in overlapping circles or a “random orbit” and remove extra wood fibers from the surface. You can affix sanding discs of varying grits to its sanding pad and forget about sawdust mess (especially if the tool is connected to a shop vac).
Estimated Cost: Somewhere between $20 and $100.
Sanding Blocks
This is a simple hand-held tool. A sanding block is a block of cork or wood used to hold sandpaper so the user can apply even and constant pressure to the wood. It creates a steady base and allows you to smoothen out imperfections from wood with comfort and control.
Sanding blocks are great for achieving a reliable smooth finish without any scratches, unlike power tools. For sanding curves, a similar product is sanding sponges.
Recommended Use: When sanding narrow spaces, quick touch-ups, intricate jobs, finalizing a larger project, or you need to apply a greater amount of pressure on a flat surface.
How it Works: Sandpaper or sanding sheets are attached to a reusable sanding block. Sanding sheets are sold separately with varying grits and you can attach whichever suits your project better. You hold the block in hand and rub it over the wood until it’s smooth.
Estimated Cost: Around $10 to $25.
Sanding Paper
Sandpaper is a piece of plastic or paper backing with abrasive particles on one side and plain on the other side. These abrasive particles are NOT sand – they’re specifically manufactured for sanding purposes.
This sanding tool is very versatile. You can use it as is, with hand sanding blocks, and power sanders too.
Recommended Use: Practically anywhere. Because of easy maneuverability, they’re best for sanding out crevices and narrow spaces where sanding blocks and power sanders cannot reach.
How it Works: When you scuff the abrasive side of your sandpaper on wood, the coarse grains grind and cut wood fibers sticking out. This removes the unevenness of wood and leaves a plain surface.
Estimated Cost: Approximately $10 to $25.
Deep Diving Into Sandpaper Grits
Sandpaper grit explains the size of the abrasive particles on it. The larger the particle size, the lower the number of particles (lower grit) in the sandpaper.
Simply put, varying grits represent the level of coarseness of the sandpaper and are usually depicted as a number ranging from P60 to P320. This grit number tells you the texture of the sandpaper.
- Low Grit Sandpaper or coarse grit sandpaper > more abrasive > quick wood removal > rougher finish
- High Grit Sandpaper or fine grit sandpaper > less abrasive > slow wood removal > finer and smoother finish
Deciding which grit sandpaper is suitable for your project is a bit challenging. Here’s a quick cheat sheet for help:
| Grit | Type | Purpose | Application |
| 16 – 24 | Very Coarse | Repairs and rapid removal | ● Removing paint ● Sanding floors and rough surfaces ● Timber windows ● Staircases ● Smoothening deep scratches |
| 40 – 60 | Coarse | Repairs and removal | ● Removing paint ● Sanding floors ● Removing scratches ● Sanding staircases (treads and risers) ● Sanding very rough surfaces |
| 100 – 120 | Medium | Preparation | ● Removing old varnish or finish ● Skirting boards ● Banisters and staircases ● Doors and door frames ● Wood furniture ● Timber windows ● Anything that requires sanding but doesn’t need repairs |
| 150 – 180 | Fine | Preparation for finish | ● Banisters ● Skirting boards ● Doors and door frames ● Wooden furniture items |
| 220 – 400 | Very fine | Finish | ● Finishing off ● Sanding between paint coats ● Sanding after paint |
| 400 – 600 | Extra fine | Polish | ● Polishing wood ● Polishing of final wood finish |
Sanding Wood by Hand
Using just sandpaper and your hands is a good way to tackle narrow spaces, make a final pass on a larger project, or finish delicate surfaces where a power sander will probably cause damage.
Hand sanding often gives better results than power sanders because you have better control. It leaves fewer scratches and makes it easier to sand contours and corners.
Step 1: Choose the Right Sandpaper or Sanding Block
The first task is getting the appropriate sandpaper for your job.
- If you’re removing a great deal of wood, use coarse-grit sandpaper
- If you’re just preparing a surface, use medium-grit sandpaper
- If you’re dealing with different types of wood and finishing requirements, you’ll need a combination of different grits.
- If sanding flat surfaces and sharp edges, use a sanding block with your sandpaper.
Step 2: Prepare the Wood
Next, you need to clean the wood surface and remedy problem areas (if any). If there are holes or dents, and the wood is worn out, use a wood filler to create a level surface. Allow the filler a drying time of up to 48 hours before the next step.
Then, grab a pencil and scribble on the wood. These pencil marks will ensure that you sand evenly across the wood and don’t remove more from one area than the rest (more on this later).
Step 3: Sand with the Grain
When your surface is clean, start sanding with a steady, constant pressure in the direction of the wood grain. Sanding with the grain minimizes sanding scratches and ensures the sanded wood is level. Scuff over the scribbled pencil lines you drew earlier until they vanish. Once the scribbles are sanded away, it’s your queue to move to the next area.
Sanding rounded edges or curves is hard if you’re using a sanding block. Switch to just sandpaper and curl your fingers around the paper to create the desired arc for sanding curvy areas.
When you’re done, slide your hand across the surface to ensure it’s consistent and level. If you spot or feel marks or dents, sand those spots again. You want to remove these marks completely with your lowest-grit sandpaper before moving to higher grits.
Higher grit sandpaper is not intended to get rid of such flaws, and painting over any imperfection will show through your stain or paint later.
Step 3: Remove Sawdust
Between grits, remove sawdust so it doesn’t get stuck between your sandpaper and the wood when you switch to the next grit. If that happens, you’d be dealing with even larger scratches in the wood than what you were trying to remove.
Remove sawdust with:
- Shop vac and vacuum up the dust
- Wipe with a clean, dry cloth
- Wet rag or tack cloth to pick up dust that the dry cloth or vacuum couldn’t remove
Step 4: Finish Off with a Finer Grit Sandpaper
Once the dings and dents are away, switch to a higher or finer grit sandpaper to remove the deepest imperfections. This will also smoothen out any scratches left by coarse grit sandpaper.
If you’re aiming for a glass-like finish, you can further switch to ultra-fine grit (600 to 800+) sandpaper after finishing with fine grit sandpaper. When done, wipe down the wood with a slightly damp or dry cloth to remove lingering dust and enjoy your workpiece.
Sanding Wood with an Electric Sander
When you need to sand a large wooden area, it’s time to bring out the big guns. Power sanders are quick, efficient, and need way less sweat and energy from you. Just like sanding with hands, first, you need to decide the grit that you’ll be using.
Step 1: Choose the Right Power Sander
Examine the condition of your wood and decide how much material needs to be removed. Pick a rough-grit sandpaper if you have thick layers of wood to be sanded off before you switch to medium-grit.
Also, consider different types of power sanders for your job:
- Belt Sanders are aggressive and powerful tools capable of removing a lot of material in a very short amount of time. The only drawback: they aren’t suitable to finish sanding.
- Random Orbital Sanders are more versatile. You can use them at almost every stage of sanding except detailed finishing, which is best done by hand.
- Finish Sanders are designed to finish sanding after a random-orbit or belt sander has removed the rougher layer of wood. Finish sanders come with fine or ultra-fine sandpaper that gives a smooth surface.
Step 2: Set Up the Sander
After choosing the right sander and grit sandpaper for your paint job, get the sander ready. Do this by loading your sandpaper onto the base of the sander. Power sanders usually have a simple hook and loop system to attach sandpaper, so you just have to peel off the old one and load the new piece.
Some power sanders may have small clamps at their sides designed to hold sandpaper in place. Inspect your sander and see which system the tool uses and line up the sandpaper onto its base.
Step 3: Sand the Wood
Some sanders require you to connect the sanding pad to the wood before starting the tool while others need to reach full speed before you can connect it to the wood. Generally, random orbit sanders need to make contact with the wood before turning them on. Belt sanders should be at full speed before they come in contact with the wood.
Once you figure that out and you’re on the workpiece, it’s time to sand.
- Sheet and detail sanders: Create back-and-forth strokes with the grain of the wood.
- Random orbit sanders: Move in long and smooth strokes with the grain. You can also go against the grain with this sander or move in small circular motions.
- Belt sanders: Work in parallel strokes with the grain to achieve a consistent finish.
Step 4: Switch to Fine-Grit and Finish
The medium-grit sandpaper used at the initial stage creates a smooth enough surface for paint or stain. But if you’re going for a bare wood look or looking for a smoother finish, switch to finer-grit sandpaper at this stage.
Using the same technique, use your fine-grit sandpaper to remove all the imperfections left behind. Go for an ultra-fine 220 grit sandpaper to achieve that almost glass-like smoothness. Sand until you see the desired results and then wipe down the surface with a dry or damp cloth to clean up.
Frequently Asked Questions
How do you sand previously finished wood?
Sanding an old fence, a piece of furniture, or finished wood is different than sanding unfinished wood. You’ll need to use a stripping solution with rough grit sandpaper to break the first coat or dark paint color.
- Apply the paint stripper and let it sit for the recommended time, and then wipe it away with a clean rag or cloth.
- Wipe the wood with a damp cloth to clean and use a power sander to sand away the top layer of the finished wood. Oil-based paints may take a little longer than water-based paints to sand.
- Switch to medium-grit or fine-grit to finish off.
Should you sand wood wet or dry?
Raw wood should be dry before you sand. Use wet sanding when you want a smoother finish with fewer scratches or when you’re at the final stages of your project.
Need Help?
Although sanding is generally a fun DIY project for many homeowners, you might not be feeling up to the challenge. That’s okay – call in a local painting pro to handle all the dusty sanding work for you.
Main Photo Credit: Los Muertos Crew / Pexels / License
