Do you have a car panel? Gate, railing or tractor part to repair and weld?
And the dang thing is rusted.
The rust on your painted metal is right there. Bubbling up through the paint.
You know you’ll need to get rid of that rust to even stand a change of welding it. And for the weld to hold.
So, you’re ready. Ready to take a flap disc to it and clean that thing right up.
But hold on a minute. Which grit should you use?
Read on and find out.
What Grit Flap Disc for Removing Rust
Pick 120 grit flap disc for removing surface rust and paint.
Pick 80 grit flap disc to take off surface rust
Pick 60 grit for deep rust and thick metal gauges. Then tidy up with a 80 or 120 grit flap disc.
Will You Need More Than 1 Grit Size To Get That Rust Off?
You’re standing there imaging what that panel ‘ll look like stripped back. And all cleaned up so you can pretty much see your face in it?
And you can get there.
But first …
Know that when you remove rust on metal that you’re going to work with a few grit sizes of flap discs.
Unless you’re dealing with light surface rust.
You’ll likely find that one grit size isn’t going to be enough. So be prepared.
And if you decide to buy cheap flap discs than you’re going to go through a few of those.
Because any paint over your rust is going to clog them up.
It’s the name of the game.
So, buy yourself a pack of flap discs.
Are you a busy dude or dudette?
And now just want to look for the best flap discs to use on rust?
Click on the button and check out the post on the best 5 on this site.
Not yet ready? Read on …
What Is The Best Grit Flap Disc For Surface Rust?
When you look at the panel or part. And can tell that the rust is just on the surface.
And you want to remove those rust spots on your metal.
Because you know there’s good metal underneath.
Or you’re not quite sure. And you want to check see what’s under that paint.
In this situation you’ll not want to take off too much.
Particularly if the metal is a thin gauge anyway.
Put your 120 grit flap disc on your angle grinder and start gently. Easing off that paint and surface rust.
120 grit is a kind place for you to start grinding your metal rust. And have a check see.
After that you can always move up to an 80 grit flap disc and be more aggressive if there’s the need.
And that rust isn’t coming off.
What Grit Flap Disc To Use For Pitted Rust
When you rub on that rust and can feel it’s more than just on the surface.
There are bits of your metal where the rust is more embedded. And you can feel those dips and peaks.
It doesn’t matter if it’s a metal railing, metal fence. Door or metal furniture you’re working on.
You can pick a 60 grit flap disc. But take care. Especially if the metal you’re working on is a light gauge.
Take a light touch. Because a flap disc used too rough risks scratching up your metal.
If you’re the type that’s a bit heavy handed then start with an 80 grit flap disc and coax that rust off.
And you’ll likely want to take a wire wheel to the pits as well. Get that railing or tractor part as clean of rust contamination as you can. Take it back to virgin metal.
Do that before you attempt to weld it back up.
When Your Panel Or Railing Is Rusted Right Through
When you can see daylight through your steel. You’ve likely left it too late for a flap disc to save you.
If there’s little or no metal to clean. Then there is little else left but to put in a new piece of metal.
Because you can’t weld on rust. If you do then the stuff’ll come back over time and you’ll be back at it fixing your part up.
You can use a 60 grit flap disc. Grind away the rusty edges. And watch those rust flakes fall to the ground.
Tidy up and grind off as much of the rust as you can with your 60 grit grinding disc.
Take the sides back to good clean steel.
If you can’t.
Then you’re left with cutting away the rusted old metal. Cut it back to where the metal is decent and can hold a weld.
And look for a piece of steel that’s about the same thickness and cut to fit the gap you have.
Tack weld it in place. And then weld up proper.
Use your 80 grit flap disc to start the blending in. And finish off with a 120 grit flap disc to smooth down and blend in your weld.
Is Aluminum Oxide Or A Zirconia Flap Disc Better For Taking Rust Off?
You’ll find flap discs come in a few surface grit types.
And you’ll notice that on the cheaper more budget friendly flap discs. They’ll have Aluminum Oxide grit surfaces.
The grit surface is what does the main work in grinding off the rust.
You’d pick Aluminum Oxide when cost is a factor for you.
The truth is that you’re going to get through a few flap discs when working on rust anyway.
So why not pick cheap and cheerful?
Pick Aluminum Oxide and you’re going to go through a lot of discs. Aluminum Oxide is not as long lasting a grit surface and will clog with rust pretty quick.
But when you’re tight on budget and not much rust to get off, it’s likely a good choice.
Zirconia and Zirconia-Alumina flap discs are more expensive.
And that’s because the grit surfaces last longer and aren’t quite as prone to clogging.
When you’ve got a large area to work on. Or you just prefer working with quality then go for Zirconia based flap discs.
They’ll last you longer. And are arguably more cost effective in the end.
Removing Rust With A Type 27 Or Type 29 Flap Disc
As well as grit surfaces you have types of flap discs. And type here means the shape of the face of your flap disc.
You’d pick one rather than the other depending on the metal surface you’re working on.
Type 27 is called a flat flap disc. But is has a 5 to 15 degree angle. Use this type of flap disc when working on flat metal. And it’s great to get into those edges and angles.
Use a type 29 flap disc for curved metal. They have a 15 to 35 degree angle on them.
Pick a type 29 and work that rounded steel.
And Before You Take Your Flap Disc To Your Rust
It wouldn’t be right to end this post without touching on safety.
Before you start. Protect your hands with some good quality gloves.
Don’t even turn on your angle grinder without your safety goggles on.
Look for the ones with side and top shields. Because those metal shards are right sneaky and will ping in at all sorts of angles.
Ideally get yourself a face shield. To protect your face. And don’t forget your neck area.
And always. Keep your grinder guard positioned to protect yourself and anyone standing near you.
Remove Rust On Stainless Steel – What Grit?
Stainless Steel doesn’t rust.
Well it’s not supposed to. But if you find rust spots turning up on your stainless steel. Then you’ve some metal contamination.
Keep your tools, brushes and flap discs separate for stainless steel. And only use them on stainless steel.
Because it’s so easy to embed mild steel into your precious stainless steel.
When you’ve got stainless steel to clean up. It doesn’t matter if its mill scale or dirt. Or some other contamination on your stainless steel. Use 120 grit for gentle removing.
And move to 80 grit when you need something a bit tougher.
Use a flap disc made to work on stainless steel.
Because you can cause rusting problems by getting your stainless steel too hot. And damaging the metal so that it loses its stainless steel properties.
Pick a flap disc that runs cool. One that’s made to use on stainless steel.
About Bill Byers
I started welding at 27 and now have over 20 years on the job experience. I MIG, TIG and flux core weld. Even done a bit of Blacksmithing in my time.
I enjoy helping novice welders find their feet.
In my spare time you’ll find me enjoying a game of football.
And on the odd weekend paying a round of golf badly. Just duck when you see a golf club in my hand.