What the MOT says

The MOT regulations used to be very clear: any patch repair had to be attached by a continuous weld all the way round its edges (ie, a seam-weld) unless a complete panel was fitted. In the case of sills, a pattern outer cover sill panel counts as a repair panel, therefore it has to be seam-welded. A genuine sill, which tends to incorporate the entire side of the car including the inner wings and door jambs, can be spot- or plug-welded.

Then, the rules changed and stated that, even for patch repairs, either spotor plug-welding (see Step 21) could be used in places where it was done so originally. This tends to be how the lower edge of a typical outer sill is attached.

Since the MOT was overhauled comprehensively in May 2018, the testing handbook provides additional clarification: “You can only pass spotwelded repairs if the original panel was spot-welded and the original panel (or section) has been removed. Stitch- or plug-welding can be used instead of spot-welding. In all other circumstances, patch repairs must be continuously seam-welded.”