How to Use Phos-Kleen B Surface Prep Fluid
Phos-Kleen B is a four-in-one acid surface prep for bare steel — a cleaner, rust remover, degreaser and phosphating solution rolled into one. Used correctly it strips a panel back and leaves a clean, lightly-etched grey surface that’s the perfect key for primer. Here’s how to use it safely and get a first-class finish.
Phos-Kleen B or Phos-Kleen A?
They’re two different products for two different jobs.
| Phos-Kleen B | Phos-Kleen A | |
|---|---|---|
| What it is | Surface prep and phosphating fluid | Strong rust remover |
| Best for | Light surface rust on panels and bodywork before painting | Heavy rust and mill scale on parts, brackets, bolts, tools |
| Finish | Blue-grey iron-phosphate coating that resists rust | Bright, bare “white” steel |
| Method | Wipe on with a Scotchbrite pad; leave to dry | Brush on or dip; watch closely |
| After | Remove residue, then paint | Neutralise, rinse, dry and prime promptly |
Dealing with heavy rust or mill scale on parts? You want Phos-Kleen A: see our how-to guide.
How to apply Phos-Kleen B
Gear up — it’s an acid
Phos-Kleen B is an acid, so protect yourself before you start: rubber gloves or gauntlets, eye protection or goggles, and a protective apron.
Apply with a Scotchbrite pad
Apply Phos-Kleen B straight from the bottle onto a Scotchbrite-type Nylex abrasive pad, and work it into the steel in a circular motion. It’s designed for flat horizontal or vertical steel panels. Don’t let it pool on horizontal surfaces.
Let it react
As it dries, Phos-Kleen B turns the steel a grey colour and leaves the surface slightly rougher — that’s the phosphate key your primer wants. Any rust down in the pits will lift as a small “nib” on the surface.
Wash it down
Wash the surface to remove any dried salts and deposits, using a fresh Scotchbrite pad with clean de-ionised water — or better still, Chlor-X DTS.
Prime the same day
As soon as the washed surface is dry it’s ready to paint. Always aim to prime the same day as the final cleaning treatment for the best adhesion.
What you’ll need
- Rubber gloves or gauntlets
- Eye protection / goggles
- A protective apron
- Scotchbrite (Nylex) abrasive pads
- Chlor-X DTS for the final wash
Phos-Kleen B FAQs
What does Phos-Kleen B do?
It’s a four-in-one acid surface prep for steel: it cleans, removes rust, degreases and lays down a phosphate coating that keys the surface for paint — all in one product.
Is Phos-Kleen B dangerous to use?
It’s an acid, so it must be treated with respect. Always wear rubber gloves or gauntlets, eye protection and a protective apron, and avoid letting it pool or dry into heavy deposits.
Why has my steel got white deposits?
You’ve used too much, or let it pool. Excess Phos-Kleen B dries to white phosphate deposits that must be washed off, as they interfere with primer adhesion. Use it sparingly and wash down afterwards.
How soon should I paint after using it?
As soon as the washed surface is dry. It’s always best to prime the same day as the final cleaning treatment so the fresh, clean steel doesn’t pick up new contamination.
Phos-Kleen B is one part of getting steel truly paint-ready. Once it’s prepped, seal the deal — see our guide to removing salts and coating failures and our 10 steps to complete rust protection.
