MGB: Ugly! Undercoating falling off! Any ideas?

I had my car soda blasted to bare metal and painted in October, 2008. Shortly after I brought it home and started putting the insides back in and the chrome back on, I noticed chips of black stuff under it from time to time. The process accelerated slowly. My wife started to notice the black stuff in the carport. I started driving it in April, but it rained a lot and then it was summer. In Mississippi. So I would drive it once every week or two, but I didn't really start driving it to work regularly until a few weeks ago. And now the undercoating is just falling off by the handful.

Has anyone experienced anything like this? Could the soda blasting or the paint baking process have contributed? (I'm not mad at anybody - just curious about what may have caused this.)

I see a big can of POR-15 in my future




.

Was the underside done when the body was stripped or is it old undercoating from the past? Hopefully it is not old from the previous owner and put on over rust.

I'd bet the paint baking booth contributed to release of undercoating.......

Jim,

There's good news and not so good news here. The negative side is that you're pretty much going to have to either let it continue to fall off, or go ahead and scrape it clean. That is obviously a lot of work. The good news is that your undercoat is apparently going to come off easily!

Last spring I tackled my left front wheel well. The 23 year old undercoating was coming off, and quickly being replaced by rust. I started scraping and sort of let the scraper go where ever the undercoat would come off. Like most jobs, it expanded and I ended up taking almost all of the undercoating off from the jacking points forward. I was fortunate to find sound, clean metal for the most part. Scrape, clean up with solvent, sand the bad patches, prime and paint. It took a couple weeks of daily work, and I got darned tired of laying on my creeper, but it was good to know the bottom is now in good shape. Picture attached is looking from the right front wheel well towards the rear.

Steve

I am missing someting here...

I can not reconcile the picture of the beautiful bodywork with the condition of hte underside. While the topside looks perfect, the stuff underneath looks typical of a 39 year old car. Not just the tin, but the lines and cables.

What all was done underneath when the car went out? Were new floor panels put in at the same time?

The stalagtites you show in the picture are behaving like neither paint nor undercoating.( Water based paint maybe?) Neither would hang in soft limp sheets like that. What I am seeing is something akin to either a latex paint that might have been put on the new floorpans, or POR put over unrusted metal or paint. POR seems to peel off if it does not have rust to bind to. I noticed rustoleum makes a water based product now, maybe it was used to protect the floorpanels?

Don't know if they still exist, but a good steam cleaning would clean up the underside and remove whatever is left of those paint boogers. Is it clean bare metal underneath?

Have you asked the body shop who did the work for their thoughts?

Pete

Jim,
Is that bare-metal showing or primer. If its bare-metal I would suspect the primer didn't bond, the soda residue was not completely removed before priming.

Thanks for the thoughts, guys. Stephen - that is one good-looking underside. Gives me something to aspire to. Did you use POR-15 and then the color coat?

The underside of my car was indeed typical of a very well-preserved 39-year-old car when it went in to the body shop. I have owned it since 1985 - bought it from a dealer when the original owner traded it in on something. The car came from NC, so it has always lived in the South. It has had almost no rust anywhere. As far as I am aware, this is the original 1974 undercoating that is coming off. (And yes, that is a great paint job on top - Dwight Burnett, Quality First, Brandon, MS.)

When it went in for paint in September, I couldn't afford to do a complete take-out-all-the-systems restoration, and the bottom (and engine, etc.) looked good enough to everybody so that I elected to have a good paint job on top and then to drive the car as I gradually worked on the systems underneath. (e.g., I'm replacing the brake system right now.)

I agree that the stalagmites look like rubber-based paint, but it all looked like regular undercoating a year ago. I certainly haven't put any paint-like substance on the bottom of the car in the 24 years I have had it. The soft, floppy stalagmites are mainly in the center of the car, whereas around the edges the undercoating is flaking off in a drier form. Could blown-back drips of the synthetic oil I put in six monthe ago be affecting the undercoating? Seems unlikely. (Nevertheless, I plan to change back to dinosaur oil today - oil drips under the car have increased markedly in recent months.)

The metal underneath the falling undercoat all looks shiny brand new just-off-the-assembly-line. (A complication for the POR-15 approach.)

Anyway, I really appreciate all your comments.

Here is one more view:

Jim,

Since my car had been undercoated, there was almost no rust after I scraped off the undercoat. In fact, I had mostly intact, body colored paint. Since things were pretty sound, I simply primed everything with Rust Oleum and brushed on 3 coats of the finish color.

Steve

It looks like some chemical has blown over it.

Maybe you are right about the synthetic oil blown back.

It looks like what brake fluid does too.

That looks like someone put paint stripper on it.

It has had silicone brake fluid for the past approx. two years.

(My mechanic said if I put silicone in, my seals would leak. And my seals did leak. But I think I just didn't do an adequate job of flushing the system, and the seals were 15-35 years old anyway. I am going to replace everything and stick with silicone.)

????

Never seen anything like that, certainly does look like a chemical reaction. If its clean metal some type of prep or etch will probably be required.

One option other than POR-15 might be the Eastwood Rust-Encapsolator. I cleaned and repainted the underside of my car about 4 years ago and the Eastwood product has held up very well. Seems to adhere well to less than perfect surfaces (like yours). Yours will certainly need priming before undercoat is reapplied, if you plan to reapply.