Body Underside finishing

Discussion in 'Chassis restoration' started by Rob Swenton, Dec 31, 2018.

  1. Rob Swenton

    Rob Swenton Well-Known Member

    I have a question about a total restoration. I am doing a 70 GS455 frame off rebuild. What are some of the ways to go when finishing the underside of the body? I am not building a trailer car. I want to drive this car when done. Some say the best way is undercoat while other say the red oxide factory finish. Still other say alot of these cars were sprayed black by the dealers when they arrived for sale. I want this car to be as "original" as possible when done. What are some of the choices I have and what have some of you guys gone with? Thanks
  2. hugger

    hugger Well-Known Member

    All the buicks I've ever seen were black with the body color overspray on the bottom. Never seen red on any A body

    My preferred method is sandblast then either go directly to epoxy prime then to paint or if a rough sand was used soften it up with 80 grit paper then epoxy.

    You can also put two coats of epoxy let cure and then hand sand if you want a really smooth surface. I wouldn't go thru this hassle on a driver myself.

    For paint I been using Sem Hot rod black urethane, it's a single stage product that's proven to be very durable, easy to apply and looks very close to OE. I like it because its repeatable and the sheen will always match. Once I'm done with the black I load up the "raptor" bedliner and spray the perimeter ie inner rockers and wheelhouse, trunk drop offs etc.

    If you want to do the whole overspray thing, then just go back with the color loaded up and with the car sitting at maybe 25° or so spray the rocker panels with a wide fan and pretend the bottom of the car isnt there and you'll get a pretty accurate representation of factory overspray.

    I don't do it very often because while correct it just looks sloppy and 99% of people will walk off thinking you were too lazy to tape off the floor,...the other handful of guys will appreciate the little extra.

    I don't care for undercoating the bottom if never really get hard and you get filthy everytime your under it especially if you get a leak or two. RAPTOR bedliner is a better option
    Last edited: Dec 31, 2018
    Daves69, TorqueMonster1 and Smartin like this.
  3. telriv

    telriv Well-Known Member

    Also the bed-liner/ undercoating act as a sound deaden-er/damper for a quieter interior when driving.
  4. wkillgs

    wkillgs Gold Level Contributor

    One of the guys here that does hi-end restorations mentioned he used Flex Seal. It will result in a smoother finish than bedliners that produce a rough textured surface.
  5. 1970 STAGE 1

    1970 STAGE 1 Well-Known Member

    You are doing the same procedure both ways . If it were my car I would go black primer with body color overspray. Undercoat the rear wheelhouses. If you duplicate the factory procedure it will be more accurate and if it is ever sold the buyer cant complain it was done wrong.
  6. Randy Lutz

    Randy Lutz Well-Known Member

    I recall reading somewhere that Framingham cars had Red Oxide floors. Just as Oldsmobiles made in Lansing could have grey undersides. My car is a Framingham car and as such the underbody of my 72 GS is still in the original Red Oxide colour.

    So I believe you need to know where your car was made before you can make a decision.

    If I am in error, kindly let me know.

  7. Duane

    Duane Member

    I'm not sure but I thought Lansing built Oldsmobile's had black bottoms. My 70 442 Conv was built in Linden NJ and it was all gray primer on the bottom with an unbelievable amount of overspray. Some areas looked like they were completely painted the blue body color.

    One thing you need to concern yourself regarding dealer installed undercoating is this;
    A guy came to my shop years ago to help authenticate his 72 Stage 1 Conv. I remember sliding under the car to see what it looked like and the undercoating was hanging down it "blisters", almost like it stopped sticking to the floor pans. Later when Kleiner started on the car he had to replace the floor under every one of those "Blisters" because water had gotten in there and rotted out the floor.

    Whatever you use, just make sure it "sticks" to the floor pan, and make sure you fix any problems on the top side, or you could end up doing more damage then anything else.
  8. dynaflow

    dynaflow shiftless...

    IMO dealer undercoating is just another way to pump up the final price. I've see places sprayed that shouldn't have been and vice versa...we could probably do a long thread on this sentence...:)
  9. 12lives

    12lives Engage! - Jean-Luc Picard

    Rob - Not to split hairs - Remember that the cars were "originally" built quickly and with little thought to rust protection. So you can restored a car to "original" and all that entails (factory markings, lack of paint and factory correct finishes) but you won't want to drive it, or you can do a beautiful looking car (better than factory- ie Hugger's post above) and have a car you can drive too. But, I will argue, you can't have both!
  10. Randy Lutz

    Randy Lutz Well-Known Member

  11. copperheadgs1

    copperheadgs1 copperheadgs1

    Both Buick’s and Olds built in Flint and Lansing for Olds had black on underside. I have been under a lot of Lansing Olds many rare W-30 and all were black like the Buicks. Even under the dash. I picked off a lot of cars in junkyard and Flint and Lansing again all black. All the Framingham cars were the red/brown underneath and under dash. It’s very obvious.
  12. Rich Johns

    Rich Johns Platinum Level Contributor

    Here is the correct way to restore underbelly.

    Pics of one of my customer's 1970 Cornet Gold 1970 GS 455 that I am restoring for him.

    Attached Files:

    Buicksky, 1970 STAGE 1 and dl7265 like this.
  13. hugger

    hugger Well-Known Member

    I can't wait to see that car done, think the 2019 Nats are possible?
    dl7265 likes this.
  14. copperheadgs1

    copperheadgs1 copperheadgs1

    That is exactly how underside of friends W-30 we are restoring looks
  15. joejbal

    joejbal Well-Known Member

    I’m looking to do a floor with the frame still on.
    It’s pretty clean except for some grease around the trans tunnel.

    What primer do you like beneath the sem hot rod black?

  16. hugger

    hugger Well-Known Member

    Just a good epoxy, Southern Polyurethanes, Ppg, Matrix etc
  17. dl7265

    dl7265 No car then Mopar

    My Leeds car's have even more then that. Almost look like a dodge on bottom with the overspray.
  18. Buicksky

    Buicksky Silver Level contributor

    Rich so does the overspray go on later for you or do you keep it clean?
  19. Rich Johns

    Rich Johns Platinum Level Contributor

    Right after I paint the 30 % gloss sheen underbelly black, all floor plugs are installed ,body is leveled out on rotisserie, body is taped off and I pretend I am a painting the lower edges of rocker panels and rear quarter panels.
    Buicksky likes this.

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