Run your hand over a clean bonnet inside a plastic bag. If it feels like fine sandpaper, your paint is contaminated — and no coating should ever go on top of that.
Decontamination is the step people skip and the one that decides whether everything after it works. Washing removes what is loose. Decontamination removes what has bonded: iron fallout, industrial particulate, tar, tree sap residue and paint mist.
First chemical — an iron-fallout treatment dissolves embedded metal particles, and a solvent lifts tar and adhesive residue. Then mechanical — a clay treatment with plenty of lubrication shears off whatever is still standing proud of the clear coat. Done in that order, the clay has far less to do, which means far less risk of marring the paint.
This is not an upsell — it is included in every coating we do. A coating bonds to the surface it is laid on. If that surface is contamination, the coating is bonded to contamination, and it will fail early.