If you’ve ever proudly spray painted something…
and then watched it start peeling like a bad sunburn two weeks later, hi, hello, you are absolutely not alone.
Most of the time, the problem isn’t the spray paint.
It’s the sanding. Or, more accurately: the lack of sanding.
Spray paint is unforgiving. It will happily cling to your project or dramatically fling itself off in flaky chunks depending on how you prep the surface.
In this post, I’m walking you through:
- When you actually have to sand (and when you can skip it)
- What grit to use on metal, plastic, wood, and old paint
- Wet vs dry sanding (yes, there is a difference)
- Primer timing, weather drama, and fixing common “oh no” moments
Let’s start with why sanding matters in the first place.
Why Your Paint Needs “Tooth” (And What Happens If It Doesn’t)
Paint doesn’t want to just sit politely on top of a smooth surface.
It needs something to grip onto—what painters call tooth.
Think of it like this:
- Trying to stand on ice = slippery, zero grip, dramatic falls
- Standing on a textured mat = your feet actually stay where you put them
Sanding creates tiny scratches and ridges in the surface. That’s the “tooth” your paint locks into. When you skip that step on the wrong surface, you get:
- Peeling from corners and edges
- Bubbling when the weather swings
- That lovely orange peel texture that screams “my first spray can adventure”
(Ask me how I know.)
When You Can Actually Skip Sanding
Good news: you don’t have to sand every single thing you touch.
You can usually get away without sanding if:
- Raw, unfinished wood
Will accept most spray paints just fine. A light scuff makes it smoother, but it will still stick without it.
- Certain plastics with special primer
Some primers are made to grip plastic without sanding. Read the can—if it says “no sanding required,” believe it (but do clean the piece first).
- Fresh paint within the recoat window
If you’re adding another coat within the time listed on the can (often 1-4 hours), the new layer chemically fuses to the last one. No sanding needed.
If you’re outside those scenarios? Assume you need to sand something.
What Are You Sanding, Exactly? (Quick Surface Guide)
Before you go ham with a sanding block, figure out what you’re working on. That drives how rough you start and how smooth you finish.
Here’s the fast version:
Bare Metal
- Usually very smooth and sometimes oily from the factory or your hands.
- Light surface rust is actually fine (kind of helpful, even).
- Start with 180-220 grit to cut through oil/contaminants and give it tooth.
- Then go to 320-400 grit before primer for a smoother base.
Plastic
Plastic is that stubborn cousin who refuses every suggestion.
- Shiny molded plastic especially loves to reject paint.
- Scuff with 320-400 grit just enough to dull the shine—don’t reshape edges.
- Use a primer that says it works on plastic (bonus points if it says “adhesion promoter”).
Bare Wood
- Paint will stick even without sanding.
- But: every bump, scratch, and weird swirl will show.
- For a smoother look, sand with 180-320 grit before painting.
Old Paint That’s Solid
Still stuck on there? No cracks? No flakes?
- Give it a light scuff with 320-400 grit to knock the gloss down.
- Fingernail test: if you can chip it off with your nail, that area counts as “failed” and needs more aggressive sanding.
Old Paint That’s Flaking or Cracked
This is the messy one.
- Sand aggressively anywhere it’s loose. Get all the failed stuff off.
- Then “feather” the edges around the bare spots with 320-400 grit until you can’t feel where the paint ends and the bare surface begins.
Primed Surfaces
- Once primer is fully cured (key word: cured, not just dry to the touch), hit it with 400-600 grit.
- You’re not trying to dig into it, just knocking down dust and tiny bumps so your color coat has a smooth runway.
Fresh vs. Cured Paint
- Within the recoat window: just spray the next coat. No sanding. You are allowed to be lazy for this brief, beautiful moment.
- Fully cured old paint: give it a light scuff with 400-600 grit so the new coat has something to grab.
Why Spray Paint Shows Every. Single. Scratch.
Brush paint is like wearing a chunky sweater: it hides a multitude of sins.
Spray paint is like HD camera lighting: it shows everything.
Each spray coat is very thin. Scratches that a brush coat would bury?
Spray paint settles into them and helpfully outlines them for you.
To avoid that:
- Your final sanding before color should usually be 320-400 grit at minimum.
- For glossy or metallic finishes, go even finer: 600-800 grit.
Also, your paint type matters a bit:
- Lacquer aerosols (strong smell, fast drying)
Each coat softens the one below, so they sort of melt together. Great for stacking coats in one session.
- Enamel aerosols (slower to cure, harder finish)
Once cured, they act like a shell. You’ll need to scuff the surface before additional coats or the new layer just sits on top without really bonding.
Not sure what you’ve got? The label will usually say “enamel” or “lacquer.” If it doesn’t, assume enamel and be a little more careful with cure times and sanding between sessions.
Your No Brainer Sandpaper Grit Guide
Think of grits as steps on a ladder—you can’t jump from the ground to the roof and expect not to break anything.
Here’s the simple version:
- 180-220 grit – “Get it under control”
– For: initial prep, removing light rust, gloss, or junk
– Goal: create tooth, remove contaminants
- 320-400 grit – “Make it presentable”
– For: refining after the first pass, bare metal before primer, scuffing solid old paint
– Goal: smooth out the 180-220 scratches
- 400-600 grit – “Smooth runway”
– For: sanding cured primer, prepping for color
– Goal: knock down dust and tiny texture
- 600-800 grit – “Fancy finish”
– For: high gloss or metallic colors
– Goal: ultra smooth base so the shine doesn’t highlight flaws
My personal rule:
Don’t jump more than about 200 grit at a time.
Going from 180 straight to 600 is like putting foundation over sandpaper and wondering why your face looks weird.
Wet vs Dry Sanding: Do You Need to Get Things Wet?
Short answer: sometimes. And it’s worth it.
When Wet Sanding Is Your Friend
Wet sanding sounds fussy, but it makes a huge difference when you want that “did a pro do this?” finish.
Wet sanding is great for:
- Metallic or high gloss finishes – water helps keep scratches shallow and smooth.
- Primer or old paint – no clouds of dust trying to invade your lungs.
- Fine grits (400 and up) – they clog fast when used dry.
How to wet sand without hating your life:
- Soak the sandpaper in clean water for about 10 minutes first.
- Keep the surface wet with a spray bottle or small bucket.
- Rinse the paper often you want that cloudy water carrying the dust away.
- If the paper starts leaving weird rubbery streaks, it’s done. Get a new piece.
- Wipe the surface dry every so often to check your progress.
When Dry Sanding Makes More Sense
Stick with dry sanding when:
- You’re on bare wood (water raises the grain and makes more work).
- You’re using coarse grits (below 320) to remove material fast.
- You need to clearly see every scratch, dent, and defect as you go.
Wet or dry, the goal is the same: a surface that looks kind of boring, dull, and even. Boring is good. Boring takes paint beautifully.
Primer: Not Magic Fairy Dust (Sadly)
Primer is important, but it does not fix a dirty, greasy, or lumpy surface.
It just locks those problems in like a time capsule.
Before You Spray Primer
Do this in order (I promise it matters):
- Clean first. Always.
Use a degreaser, wax & grease remover, or even a good scrub with soap and water (and then let it fully dry). Skin oils, car oils, weird mystery grime—all of it kills adhesion.
- Sand for tooth
Use the grit that matches your surface:
– Bare metal/plastic: start 180-220, refine to 320-400
– Old solid paint: 320-400 scuff
- Feather any transitions
Where bare spots meet old paint, smooth those edges with 320-400 until you can’t feel the step.
After Primer Cures
Key word again: cures, not just “doesn’t feel sticky.”
- Wait the full time
Most primers need at least 24 hours. Some heavy build types need 48-72. If you press hard and it still takes a fingerprint, it’s not ready. Ask me how I gouged a whole panel learning this.
- Sand with 400-600 grit on a block or foam pad
This keeps you from digging trenches with your fingers and helps you keep everything flat and even.
- Clean off the dust
Blow it off or wipe well, then go over it with a tack cloth. One lonely speck under metallic paint can look like a moon crater later.
Once your primed surface feels smooth, even, and slightly dull, then it’s time to think about color. But first…
Weather: The Invisible Saboteur of Spray Paint
You and your paint are now in a relationship with the weather. You didn’t ask for this, but here we are.
Ideal conditions:
- 65-85°F (18-29°C)
- Under 60% humidity
Outside that range, you’re kind of gambling with indoor dry time and safety.
- Too cold:
Paint stays soft forever. You wait longer to sand, and it’s easy to gouge or clog your paper because the paint’s still gummy underneath.
- Too hot:
Paint dries mid air and lands rough, or it dries the second it hits the surface and can’t level out. Hello, texture and orange peel.
- Too humid:
Water based stuff just… doesn’t dry. Solvent based paints can turn cloudy (called “blushing”), especially in clear coats.
Also: try not to spray in direct blazing sun. Surfaces get hotter than the air, which means your paint can dry on contact instead of bonding. Shade is your friend.
Spray Technique That Saves You From Extra Sanding
Most of the sanding “emergencies” I see happen because of one of three things:
- Spraying too close
- Spraying too heavy
- Spraying with a cold, badly mixed can
Quick Technique Checklist
- Shake the can like you mean it.
When you think you’re done, give it another 30 seconds. That little ball inside is your only employee. Make it work.
- Warm up a cold can.
If it’s been living in a chilly garage, stand it in warm (not hot) water for a few minutes. Warm paint sprays smoother.
- Stay 8-12 inches away from the surface.
Closer = runs and sags you’ll be sanding out later.
Farther = dry, dusty overspray.
- Use thin coats.
Two or three light passes with a short wait between will always beat one heavy “let’s get this done” coat. Heavy coats love to drip, run, and crack.
Your future self, who is not standing there furiously sanding out runs, will thank you for smarter spray methods.
How to Fix Common “I Messed It Up” Moments
You will mess something up at some point. That’s not a threat; that’s DIY.
The good news: most mistakes are totally fixable.
- You sanded through to bare metal or plastic
Annoying, not fatal.
→ Spot prime that area, let it fully cure, sand the primer to blend, then repaint.
- Your sandpaper keeps clogging instantly
The surface is probably still too soft, or you’re using too fine a grit dry.
→ Give it more cure time, switch to wet sanding, or step down to a slightly coarser grit.
- Scratches are showing through the paint
That’s your sign you either finished too coarse or skipped a grit jump.
→ Sand back down to primer with the right grits in between (no giant leaps), then repaint.
- Weird craters or spots where paint pulls away (fish eyes)
That’s contamination—usually oil, wax, or silicone.
→ Sand the area smooth again, clean with a proper wax & grease remover, and respray.
Deep breath. It looks worse mid fix than it will at the end. Promise.
Metallic Paint: The Drama Queen of Finishes
Metallics are gorgeous, but they are absolutely not chill.
They use tiny flakes that reflect light, which means:
- Flakes lay differently over smooth vs scratched areas.
- Any defect in your prep turns into visible stripes, blotches, or weird dark patches.
If you’re using metallic spray paint:
- Go one grit finer than you would for solid colors.
– If 400 grit is okay for normal paint, use 600 for metallic.
– Want a really slick look? Go to 800.
You’ll know you’re ready for primer when:
- The bare surface feels even
- No slick, glossy patches
- No deep scratches catching your nail
You’re ready for color when:
- The primed surface feels smooth and consistent
- Dust nibs and specks are gone
- It looks flat and slightly dull
Shiny comes later. Right now you want dull, even, and frankly a little boring.
The Real Secret: Don’t Rush the Boring Parts
Spray paint success is basically:
- 10% choosing the color
- 20% actual spraying
- 70% sanding, cleaning, and waiting for things to cure
If you:
- Match your sanding to the material (metal, plastic, wood, old paint)
- Use sensible grit steps (no giant jumps)
- Let primer and paint actually cure before you attack them
- Work with the weather instead of against it
- Keep your spray coats light and controlled
…you’ll get that “wait, you did this at home?” finish instead of the “oh, that’s… a choice” finish.
Start on something small to practice—an old picture frame, a plant pot, a thrifted metal box. Once you see how much difference the prep makes, you will never look at sanding as “optional” again.
Prep is where the magic happens.
Scratch it right, and your spray paint will actually stick around for the long haul.