Welding, Filler & Plating: What Passes the NCT
Updated 2026-10-03.
A corrosion failure is a reason to understand the affected structure before paying for a repair. A tidy-looking surface does not show the condition of the steel underneath. Start with the failure report and an inspection of the damaged area.
What the Official Manual Says
The NCT manual, corrosion assessment and repairs sections, pages 10-12 and chassis section 6.1.1 distinguishes primary structure from secondary bodywork. Body-filling compounds alone are not acceptable repairs to primary structure. It describes welding replacement metal of matching gauge and permits filler or fibreglass for cosmetic smoothing of non-structural parts.
Chassis checks include the condition of structural members, welds, security and corrosion. Repair suitability depends on maintaining original strength. A visibly unsafe chassis or underbody repair may require a modifications report. These requirements do not mean that every welded repair guarantees a pass or that every rust defect has the same severity.
What That Means for Your Repair
At Quinn Engineering, our structural corrosion work involves removing damaged steel and welding replacement sections into sound metal. We assess how far the damage extends before agreeing the work. A sill problem may involve both the visible outer panel and hidden inner structure. A floor repair may involve adjoining support sections as well as the visible hole.
Ask what will be removed, what will be replaced and how the surrounding structure will be checked. Covering the damaged area can conceal corrosion that still needs attention. Photos taken during the repair help explain the work, but do not replace the test centre’s inspection or any required professional documentation.
See our underbody welding service, sill repairs and actual workshop projects for examples of the work we handle.
Before Arranging Work
Keep the complete NCT failure report. Send the exact wording rather than a summary such as “rust underneath”. Tell us about previous repairs and your test or retest date. Discuss any supporting documentation requested by the test centre before agreeing substantial work.
Do not assume that repairing one corrosion item resolves every test defect. Check the complete report and arrange the other work separately where needed. Follow the test centre’s instructions about whether the vehicle can be driven. If its safety is uncertain, discuss transport before bringing it to the workshop.
Get an Initial Assessment
Our workshop is in Ardaghy, Omeath, Co. Louth, about 20 minutes from Dundalk. Call 083 807 7144 or send photos on WhatsApp.
Include the make, model, year, your town, a wide photo and close-ups taken safely. An initial photo assessment helps us discuss the next step. A workshop inspection confirms the scope and price before you decide to proceed. Call before travelling to discuss availability.
You can also read our chassis repair cost guide to understand what affects a quote.
Frequently Asked Questions
Can a structural repair guarantee an NCT pass?
No. A repair can address an identified defect, but the test centre assesses the whole vehicle and decides the result. Other defects or required supporting documentation can affect that result.
What should I send for a repair assessment?
Send your vehicle make, model, year, town, clear photos and the exact NCT failure wording. Include your retest date. Photos help with an initial assessment; inspection confirms the work and price.