UC-202 presents the basics of UNDERCOATING REMOVAL (perish the thought).

Dick Masse wrote:
    >"The body is partially covered with undercoating.... should this be removed prior to painting or if its in good shape, should it be left on. If it needs to come off how does one accomplish that?"

Removing undercoating is a real PITA (to put it mildly). If you go to the trouble of disassembling everything for a complete restoration you can take it to RediStrip to have it dipped and chemically stripped. Otherwise it's a LOT of really horrible scraping to do, and some of the surfaces are a bear for access. Some people say that the stuff is easier to chip off if it's frozen, but you almost have to be a masochist to work outside in the winter to do that. Attempting to chemically strip a heavy layer of undercoating in your home garage may take buckets of paint stripper and weeks of repeated soaking. This has to be one of the nastiest chores in restoration work. All I can advise is to wear a rubber suit and heavy gloves and come armed with some stiff brushes, scrapers and chisels (and lots of time and patience). Whether you do this or not depends on if the body sills need some sheet metal replacement, or if the frame might need patching.

First you need to determine the condition of the sheet metal, especially the parts inside of the sills next to the frame. If it is truly solid (not very likely actually), then you can leave the undercoating alone and go after the external paint job. These cars were seldom ever undercoated when new, so we first suspect that the undercoating was applied later in an attempt to cover up some significant rust (until proven otherwise). Nothing mean spirited about this, just a matter of experience. The MGA body sills are assembled from three pieces of sheet metal which form a box section with an added contoured outer cover. This was originally painted on the outside only, leaving four internal surfaces exposed to the elements to rust, and they do rust in all but the driest of climates. Read more on rusty sills in the Restoration section under Opening Your First Rustbucket under Restoration Tech. In essence, the only way you get away with not removing undercoating would be if the original application was accompanied by a very good internal rustproofing treatment. If you have any rust perforation of the panels, of any places where the undercoating pulls off and exposes rust underneath, then it all has to come off.

(Shiver)...,
Barney Gaylord