How do I prepare a car for polishing?
Quick answer: Wash the car thoroughly with a proper car shampoo -- clean bucket, fresh solution -- and hit the missed traps: under mirrors and number plate, arches, sills, door shuts and roof rails. Dry off, then feel the paint with a dry microfibre. If it's rough, consider a light clay bar; light tar or sap often comes off with the polish itself. If you can see gritty black or orange particles -- heavy industrial fallout -- speak to a professional.
Regardless of what kind of car you have or what type of paintwork it has, preparing it properly before polishing really matters.
There is no magic to this -- you just need to get the car genuinely clean. People often rush the wash, and then, because they are taking great care with the polish, they suddenly notice every spot they missed. Those missed spots tend to be exactly where dirt and grit collect.
What happens next is that you drag your polishing sponge through the grit and start rubbing it all over the paint, inducing swirl marks and scratches.
The spots almost everyone misses
A foam kneeling pad from a garden centre helps enormously -- many of the traps are low down and invisible while standing next to the car. A step to stand on is useful for checking the roof too. The specific spots to check are under the wing mirrors, around the rear number plate, inside the wheel arches, under the bumpers, sills and valance, inside the door shuts, and under any roof rails or strips.
We'd recommend using a traffic brush to help get into all the gaps -- not any old brush, this is a specific type.
How to wash it properly
There's a lot of advice online about how to wash a car, much of it written by enthusiasts who are fastidious about avoiding wash marks. They love cleaning cars; you probably don't, and that's fine. There are simpler methods that don't involve grit guards and the two-bucket method, and you don't actually need any of that to get the same results.
Get a bucket, use a proper car shampoo (not dish soap), don't let the water get too dirty, and be aware that grit sinks to the bottom -- so if you let your sponge or wash mitt drop to the bottom of the bucket, it will pick up that grit.
There's also a taboo about sponges in the enthusiast community because they're hard and flat and can trap grit. A wash mitt and/or a traffic brush is preferable without question, but if all you have is a sponge, don't worry about it too much. If you're polishing because you already have wash marks, switching to a wash mitt now is shutting the door after the horse has bolted. Get one for next time once the car is polished.
Check for contamination after washing
Once the car is washed and dried, run your hand over the paintwork or drag a dry microfibre cloth across the panels. A smooth surface is ready to polish. A rough or gritty surface needs decontaminating first -- and that step matters more than most people expect.
Iron particles from brake dust embed in the clear coat and don't wash off. They look like tiny black or orange dots and stay bonded to the surface no matter how hard you scrub. If you run a polishing compound over that surface without dealing with them, the pad picks up the particles and drags them across the panel -- turning prep into marring. Tar and tree sap behave the same way: the wash won't shift them, so they end up smeared and spread by the compound.
Clay bar, iron remover and when to call a professional
For light tar or tree sap, the polish itself often has enough solvent to lift it -- try polishing first and inspect. If the surface still feels rough afterwards, or feels rough before you start, a clay bar is the next step. Clay glides over the paint with a lubricant and physically shears off bonded contamination -- iron, tar, sap, overspray -- that washing can't reach. Afterwards the surface will feel noticeably smoother.
For heavier iron contamination (the orange or reddish particles that turn a microfibre rust-coloured), an iron fallout remover spray is a cleaner first move. It reacts chemically with embedded iron and turns purple as it works, so you can see exactly where the contamination is. Rinse it off, then assess whether you still need a clay bar pass. That combination -- iron remover first, clay bar to finish -- is the standard pre-correction sequence in a professional workshop before any machine polishing begins.
If the paint is heavily contaminated across multiple panels with visible black or orange grit, that points to industrial fallout that is beyond a DIY clay bar. Speak to a professional about proper decontamination before polishing -- abrasive work on heavily contaminated paint will make things worse, not better. For the full pre-polish assessment, see the car polishing preparation overview.