Professional systems for weather like ours
RPNI Approved Centres use professional Mercasol or Noxudol corrosion-protection systems selected for the vehicle and treatment specification. These Auson AB systems were developed in Sweden for salted roads, constant damp and freeze-thaw conditions — the same corrosion pressures created by Atlantic moisture and winter gritting in Ireland.
Rust rarely starts where you can see it. It starts inside sills, box sections and chassis seams, and under the floor — and even a nearly new vehicle can begin corroding after a few Irish winters. Treatment costs a fraction of the repair, and far less than the value lost at trade-in.
Why inspection comes before protection
A previous coating does not tell you whether the metal underneath is sound.
The vehicle in this video had received an earlier treatment over existing rust. Corrosion continued beneath the coating until the vehicle was too badly damaged to repair and was written off.
Our inspection found that the first two stages of any proper treatment had been skipped: the underbody was never cleaned and the existing rust was never removed. The coating was applied straight over it, and the products used were not suitable for the job. Sealed in under the wrong coating, the corrosion spread faster than it would have on an untreated vehicle.
Previous treatment, vehicle subsequently written off
The RPNI process starts with assessing the vehicle’s condition and the preparation it requires. Existing corrosion must be assessed before a suitable treatment can be recommended. Some vehicles will require repairs first; others may already be beyond repair.
How the treatment is done
This is not a quick spray over dirt. A properly prepared and documented treatment can take the best part of two days, and every RPNI Approved Centre follows the same seven-stage process:
Download the professional treatment guide
Strip & deep-clean
Underbody covers, guards and access plugs are removed. The underside and cavities are thoroughly washed to remove dirt, oil, road salt and loose rust. Existing corrosion is prepared first, with local blasting where required.
Dry with a hot airstream
Warm, high-volume air is directed through the underbody and cavities until trapped moisture is removed and the vehicle is completely dry.
Mask & protect
Brakes, hoses, driveshaft boots, electrics and connectors are carefully masked before any treatment product is applied.
Penetrating wax
Mercasol 831 ML — a thin, creeping cavity wax — is injected into sills, box sections, doors, bonnet and tailgate edges, underbody seams and wheel arches. It works into seams and welds where corrosion starts first.
Overnight cure
The vehicle is left for at least 12 hours so the cavity wax can settle deeply into the metal before the protective wear layer is applied.
Tough wear layer
Mercasol 847 AL — a flexible, wear-resistant underbody coating — is applied over the floor, wheel arches and sills, forming a durable barrier against moisture, salt and stone impact.
Inspect, register and certify
Removed covers are refitted, coverage is checked, and the completed treatment is photographed and registered. A numbered Vehicle Rust Protection Certificate & Inspection Record is issued for online verification, with inspection every two years where the vehicle is participating in the renewable protection programme.
Professional products, independently administered
Mercasol and Noxudol are professional corrosion-protection product systems manufactured by Auson AB. RPNI independently trains and assesses participating garages in Ireland, maintains treatment records and administers its own programme; product use does not imply government, vehicle-manufacturer, insurer or NCT approval.
Mercasol and Noxudol treatment systems
Cavity protection
Mercasol 831 ML: a thin, penetrating wax that creeps deep into closed sections and seams.
Underbody protection
Mercasol 847 AL: a tough, flexible underbody coating with rust-inhibiting additives.
One system
Selected and applied by trained applicators at RPNI Approved Centres, then inspected and entered in the vehicle treatment record.