Painting or undercoating or not?

[Soterik]

One of my cars is in the middle of the paint process. Car is bare metal, all issues have been fixed (very few, lucky me!).

The question is what to do to the underside. Currently with the exception of paint the car is extremely original. It's a targa, and still has the original targa top material and headliner, intact and very nice shape. The interior is beautiful and also completely original except for the addition of sport seats.

The undercoating on the car is all original... a few flaking in some spots but overall pretty darn nice. I was thinking of just dropping the suspension and painting that (no powdercoat), and just leaving the underside original. OR, I can just "paint" the original undercoating (not undercoat). Or scrape the whole thing (seems a shame) and start over.

I'm leaning towards just leaving the original undercoating alone for all the world to see, but still restoring the suspension.

Opinions?

[AlfaGTA]

I would vote for cleaning the undercoating and touching up any places where it has chipped off or gotten too thin, but otherwise leaving it alone. Bill M

[304065]

Erik,

If the car is an LWB, do your best to keep it in place, clean it and touch it up and repaint it. That's not easy to do, but the best option given the tenacity of the LWB undercoating and the fact that it's probably working as designed. (None of my advice factors in the approximately 50 hours it will take).

If SWB, I would think very hard about removing it. The SWB undercoat was applied over bare metal- with the result that it's often flaking off and rust has formed underneath it. Good news is that it can be steel shot blasted off, although the more tenacious areas may require the use of the Wuerth undercoating tool or a propane torch and scraper to remove.

This will allow you to get the undercoating off in the troublesome spots, e.g. up in the rear fender wells, behind the door latch area, trunk release cup/conduit, around the rear seatbelt receivers and the real problem spots, up under the chrome trim for the rear windows.

Replicating the SWB undercoat is not all that difficult and I would think you would leave a better impression if all the dings were worked out of the pan and everything was one, even color with a consistent texture.

[MarkS]

Having just finished the removal process on my 67 I noted that even though the undercoating was 95% intact with a few chips/flaking like you described moisture had migrated to surrounding area's up to 12" diameter in some areas and rust was present even though the coating appeared intact and well bonded. My suggestion, pick a flaked area and remove a bit at a time to see if yours has done the same, if not touch it up and paint. SEM makes a product called 'trim black' that was a dead ringer for my old aged undercoat. Sounds like you found a keeper.

[denson]

"S" "O", I say clean her up with a light power wash and touch up the areas you need to. I would take the suspension apart, re-paint it, do the bushings, and be done. This way, she looks mostly original with a spanking new suspension. I did this to my rs in June 09 and when she is up in the air it looks nice.

It sounds like a real nice car. The best of luck with it.

[kenikh]

Do what I did to the SWB...scrape away every flake that will come loose, then touch it up. It will blend. BTW, SEM Trim Black is the SH!T...good call, Mark. That stuff is indeed a dead ringer for SWB black.

[304065]

Do you gents mean the color of trim black is the same color as the old undercoat? I don't think SEM trim black has any texture to it.

[MarkS]

Do you gents mean the color of trim black is the same color as the old undercoat? I don't think SEM trim black has any texture to it.

You are correct it dosen't have any texture, touch it up with Wurth then spray/mist over with SEM. On my 67 the SEM was VERY close to the old undercoat when I touched up luggage compartment, one side was 100% the other required touch up with Wurth then a spray with SEM it then matched the untouched side. I would hesitate to say on the pan since it has had exposure the luggage area has not and the fact I completely stripped the underside.

[DynoDave]

Eric,

I am with Mark S and Kenikh. I would power wash and scrape back the areas that are peeling / flaking to make sure that you remove all of the loose undercoating. Treat the bare metal with a good metal conditioner (Sikkens Anti-Static Cleaner works very well on bare metal), spray some epoxy primer over the bare metal (or zinc chromate), then coat with Wurth Undercoating and blend in the Sem trim black. This is all based on the premise that you do not have large areas of undercoating break away from the metal when you power wash and scrape. As you know, there is no easy way to do this. 304065's response is dead on. If you do need to remove all of the undercoating and opt to use steel shot, make sure that the person doing the blasting is competent. It is possible to warp and damage the metal if to much air pressure is used or they stay in one area for to long, not to mention the additional clean up work you will have to do if the car is not thoroughly masked off and protected from the blast media. You will know which way you need to go (touch up or complete) after you scrape several different areas.

Dave

[preS]

Eric,

If the original undercoating has quite a few of flaking on several spots and you plan to drive your car in the rain too, than in my opinion the best approach is:

- dry ice blast to remove all the undercoating
- sand/grind lightly the bare metal
- media blast the rust(y) spots
- acid treatment (WO1)
- apply epoxy
- apply undercoating
- paint over the undercoating. Not original but recommended if you do drive the car.

If your current undercoating is actually pretty good I just would do a partial treatment and touch it up as suggested by Dave, Mark and Kenik.

Last of course it also depends on how you plan using your car after it's done.

just my $.02

Richard