How to Use Phos-Kleen A Rust Remover
Rustbuster Phos-Kleen A is the strongest rust remover in the Rustbuster range. Brush it onto rusty steel, or dip smaller parts in it, and it fizzes away rust and mill scale to leave clean, bright, bare metal, often in minutes rather than hours. It’s the go-to for heavily rusted brackets, bolts, tools and restoration parts that need to go back to bare steel before painting.
That strength needs respect, though. Rustbuster describes it as something to think of as a “metal remover”: once the rust is gone it will carry on into good steel. Used properly, it’s fast and very effective. This guide shows you how.
Phos-Kleen A or Phos-Kleen B?
They’re two different products for two different jobs.
| Phos-Kleen A | Phos-Kleen B | |
|---|---|---|
| What it is | Strong rust remover | Surface prep and phosphating fluid |
| Best for | Heavy rust and mill scale on parts, brackets, bolts, tools | Light surface rust on panels and bodywork before painting |
| Finish | Bright, bare “white” steel | Blue-grey iron-phosphate coating that resists rust |
| Method | Brush on or dip; watch closely | Wipe on with a Scotchbrite pad; leave to dry |
| After | Neutralise, rinse, dry and prime promptly | Remove residue, then paint |
Doing bodywork with light rust? You want Phos-Kleen B: see our how-to guide.
How Phos-Kleen A works
Phos-Kleen A is a blend of phosphoric acid, a urea-based acid and a wetting agent. The 2024 formula is hydrochloric-acid free. As soon as it touches rust you’ll see it fizz: the acid is dissolving the iron oxide and lifting mill scale from the surface. It works from the surface down, so it removes the rust first. But it doesn’t know the difference between rust and good metal, so once the steel is clean it keeps going. That’s why timing and supervision matter more with Phos-Kleen A than with any other product in the range.
✔ Great for
- Heavily rusted brackets, bolts, hinges and small parts
- Removing mill scale from new steel before painting
- Restoration parts that can be dipped
- Rusty hand tools
- Getting back to bare metal before an epoxy primer
✕ Not for
- Petrol or diesel tanks: use the Slosh & Tank-Kleen kit instead
- Large panels with light rust: use Phos-Kleen B
- Anything you can’t watch while it works
- Non-steel metals: ask us first
How to use Phos-Kleen A: step by step
Gear up and set up
Put on your PPE and set up outdoors or in a well-ventilated space. If you’re dipping parts, use a plastic container with a lid, never a metal one. Have fresh water (or Chlor-X) ready for rinsing before you start.
Clean and degrease the part
Acid can’t get through oil and grease, so remove any heavy dirt and knock off loose, flaking rust with a wire brush. Degrease with Rustbuster Safer Degreaser or SP10 and rinse. A clean part gets an even result.
Brush on, or dip
For larger items or parts you can’t remove, brush Phos-Kleen A directly onto the rust. For small parts, submerge them in the container. Either way you’ll see it fizz as it attacks the rust and mill scale.
Watch it closely, and take it out as soon as it’s clean
This is the step that matters most. Don’t walk away. Check the part every few minutes, and as soon as the rust is gone and you see clean, bright steel, stop the reaction. Heavy rust may need a scrub with a brush and a second application rather than a long soak. Never leave parts in overnight.
Neutralise and rinse
Stop the reaction by neutralising with Rustbuster Chlor-X (the direct-to-surface formula) or plenty of fresh water. Rinse thoroughly, including inside holes and threads, so no acid is left behind.
Dry and prime the same day
Freshly stripped steel is completely unprotected and will start to flash rust quickly. Dry the part thoroughly and prime it as soon as possible, ideally the same day. Custom 421 Epoxy Primer, Zinc Rich Epoxy-Anode or Epoxy Mastic give the best protection on bare steel. Rinsing a lot of parts? Adding Bor-X to the rinse water helps stop flash rust while they dry.
Mistakes to avoid
- Leaving parts to soak unattended. Once the rust is gone it starts on good metal. Stay with it and check often.
- Using a metal container. The acid will attack it. Use plastic.
- Reusing brushes for paint. Brushes can be washed in fresh water, but once they’ve been used with Phos-Kleen A, don’t use them with any other liquid or paint.
- Using it on fuel tanks. It isn’t suitable for petrol or diesel tanks. Use the Slosh kit.
- Leaving bare steel unprimed overnight. Flash rust will undo your work. Prime the same day.
- Skipping neutralising. Acid left in seams and threads keeps working under your primer.
Sizes: Phos-Kleen A is available in 1 litre and 5 litre bottles. If you’re unsure whether it’s right for your job, contact us before you buy. We’re happy to help.
Phos-Kleen A FAQs
What is the difference between Phos-Kleen A and Phos-Kleen B?
Phos-Kleen A is a strong rust remover that strips heavy rust and mill scale back to bare, bright steel. Phos-Kleen B is a milder surface-prep fluid for light rust on panels: it phosphates the steel, leaving a blue-grey coating that resists rust before painting. They’re used for different jobs, not together.
How long should I leave parts in Phos-Kleen A?
Only until the rust is gone. That can be minutes, depending on how heavy the rust is. Check every few minutes and remove the part as soon as the steel is clean. Never leave parts soaking unattended or overnight, because it will start removing good metal.
Is Phos-Kleen A a phosphoric acid rust remover?
Yes. It’s based on phosphoric acid combined with a urea-based acid and a wetting agent. The current 2024 formula contains no hydrochloric acid.
Can I use Phos-Kleen A at home?
It’s designed for industrial use, but DIY restorers can use it safely if they wear full PPE (gloves, eye and face protection, mask and protective clothing), work in a ventilated area and never leave it unattended. If you’re unsure, contact us before buying.
Can I use Phos-Kleen A to clean a fuel tank?
No. It isn’t suitable for petrol or diesel tanks. Use the Rustbuster Slosh Fuel Tank Sealer & Tank-Kleen kit, which is made for the job.
What do I do after using Phos-Kleen A?
Neutralise with Chlor-X or plenty of fresh water, rinse thoroughly, dry the part and prime it the same day with an epoxy primer, because bare steel flash-rusts quickly.
More on getting steel ready for paint: Surface Preparation, Rust Remover vs Rust Converter and how to use Custom 421 Epoxy Primer.
