MG Car Repair: MGB undercoating, drainage holes, surface rust

Question
QUESTION: hi Howard - I have an MGB 1974 that has been undercoated and would o be at least 5 years ago before I bought it. It is fairly thick but pliable tar texture black coating. I am wondering should I remove it as I suspect rust may be forming below? If so, what is the best way to re-protect?. Thanks

ANSWER: Hi Paul,

Most of the car was factory undercoated but if someone added undercoat and it is blistered up or bubbled up in places you can scrape a suspected small section off to see if it is rusting under it. If not you can just recoat that section with spray undercoat.

Most every place an MGB rusts are not undercoated like the lower quarter panel between the door and the wheel arch. Also the rocker panels and the lower front fenders between the wheel arch and the door. check the floor boards on the inside under the mats and insulation.

Almost all MGBs rust in those areas and they rust from the inside because they were not properly treated. There are small drain slots for each but they are easily stopped up.

Howard

---------- FOLLOW-UP ----------

QUESTION: Thanks Howard - assuming I do find some rust either on the underbody or inside floor areas - and aside from removing it, adding drainage holes, how much rust is deemed serious enough to undertake remedial work ( welding on steel plates etc...)? Is electrostatic treatment an option to arrest the rust?

Answer
That totally depends on how far you want to carry a restoration. If you find that there are places so rusted that the metal has holes or cracks then you should remove the undercoat in that area until you find good clean metal to weld to. But if it is just surface rust that can be sanded or sand blasted to clean metal you would be better off just cleaning and treating only the rusted spots you find.

Some people who are restoring a car from frame up just have the whole car dipped and start from scratch. But many just check trouble spots by removing the paint and undercoat in areas that look blistered or cracked and clean and sand blast only the rusted areas and then just prim, paint and recoat with undercoat.

I have done several cars that I found several holes in the floor panels and rather then patch them I removed the whole floor panels and replaced them but for example on that same car it had holes in the lower rear fenders but on some cars it is a large job to replace a rear fender but several sizes of "Patch Panels" are available so I usually just mark and cut the lower part of the fender off and weld in a patch panel. The same is true on the front fenders except I usually will replace the whole lower half with a patch panel. If a rocker panel has holes I will replace the whole rocker panel for two reasons. One is that often on a MGB if you have holes in the rockers, there is a good chance there is a problem with the next vertical panel inside which also needs attention.

I don't usually cut and weld unless there are holes and/or cracks. Floor panels are notorious for cracking under the seats in a MGB. On my latest MGB-GT project car I not only replaced the floor panels but added one by one braces under both seats to prevent floor panels from cracking in the future.

Howard