Underside OEM Finish's

[Randalla]

I'd like to find a complete description of how the underside of a 240Z (floors, inner fenders, components, etc.) was finished from the factory. I have to believe there must be a post on here somewhere, but I have searched on a number of topic descriptions to no available. Can anyone help? Thank you.

[CanTechZ]

This is a good topic, I believe the finish on the underside evolved over time. My 7/70 car had the heavy tar like undercoating that was dealer applied. in all of the areas that I have removed it, the finish that is exposed is body color paint. This includes the floor underside, front and rear wheel wells etc. and no factory undercoating.

Here is one discussion I have bookmarked:

 

Edited June 15, 2020 by CanTechZ

[jfa.series1]

Here are a couple of before and after dirt removal pics on my one-owner car - please excuse the color tint on the second pic. Always a Dallas area car, no undercoat or other protectant applied. As you can see, body color all the way.

[Randalla]

Thanks to both of you for the great reference. My 1972 Z has been in AZ all its life and I've begun cleaning the bottom up. It appears the underside of my car has a lot of road grime, but no factory undercoating. I've found that a combination of using kerosene and/or hot steam loosens the grime, that can then be wiped off with an absorbent towel. It's definitely slow going but the results are looking like it will be worth the effort. I'm probably one of the few anal enough to actually care. I'll post some images as I make progress. Thanks again   

[87mj]

I always thought the underneath side of the car wasn't finished at all.  Jim's pics seem to support that.  In other words, they were barely painted and painted mostly by overspray.

[Randalla]

While the picture of the underside of Jim's car is obviously not the kind of paint job the body got, it sure looks like more than over-spray. It has been rewarding to uncover factory paint underneath as I go. As an aside, I'm not a fan of seeing the ragged pinch weld along the bottom of each side, which is typically a little beat up. I've resorted to straightening any "jacked" edges, sanding the outside edge, and then masking and spraying it semigloss black. No, it's not factory but to my eye it really cleans things up when viewing the car in profile.

[jfa.series1]

I'm pretty sure the entire underside had a coat of primer that was followed by a "casual" application of body color. Certainly nothing as intense as we see today with rotisserie repairs and paint.

Edited June 16, 2020 by jfa.series1

[Patcon]

3 hours ago, Randalla said:

While the picture of the underside of Jim's car is obviously not the kind of paint job the body got, it sure looks like more than over-spray. It has been rewarding to uncover factory paint underneath as I go. As an aside, I'm not a fan of seeing the ragged pinch weld along the bottom of each side, which is typically a little beat up. I've resorted to straightening any "jacked" edges, sanding the outside edge, and then masking and spraying it semigloss black. No, it's not factory but to my eye it really cleans things up when viewing the car in profile.

I had planned on blacking that lip out also. I can be a "little" compulsive too...

[inline6]

My 6/71 and 12/70 both have the same black "undercoat" which was liberally covered in overspray.  The coating is quite tough.  It is not tar based at all, but more like a truck bed liner material, believe it or not.  The texture is not as rough as typical truck bed liners.  The thickness is something like 1mm as a best guess.  On impact areas of my car, I have been using 80 grit on a DA to feather edge, sanding to bare metal while feather edging.  There is no primer on the bottom of the car.  Just this stuff.  Least amount of overspray is in the tunnel.  All four wheel wells appear to be intentionally sprayed with color.  Car is silver - hear are some pics:

 

    

    

 

In some areas such as the back of the spare tire well, they really loaded it on causing runs...

    

 

No primer underneath this stuff, at least on the bottom of the car.  Front wheel wells may have primer under the "undercoat":

    

[Randalla]

inline6, this is excellent reference. Thank you for posting this. What are your intentions on your project? Looks like you're prepping for a re-spray. Will you respray something approximating the original undercoat and then spray color?

[jfa.series1]

Here's a couple of additional reference pics after the car was cleaned. Different/inconsistent treatment of left and right.

[inline6]

5 hours ago, Randalla said:

inline6, this is excellent reference. Thank you for posting this. What are your intentions on your project? Looks like you're prepping for a re-spray. Will you respray something approximating the original undercoat and then spray color?

I am restoring a 240z I purchased on Bringatrailer.com.  Here is the auction I won.   And I have been pretty active with updating a build thead here on this site.  Lots of pics and detail showing the work involved.  

Regarding the plan for undercoat, I spent a lot of time looking for options and think I can do a decent job of replicating the original undercoat texture.  Most truck bed coatings have too rough of a texture.  Most undercoats have tar in them, which the original coating does not have.  Most paints are too thin.  I found a truck bed liner (Raptor Liner) that looks close, and I plan to experiment with replicating the settings and application technique used by the Gunman in this video.  If you jump to 21:55, you can see a couple quick close ups of the finished texture.  Still a bit course, but close.  

I also got a Raptor liner kit that came with a variable nozzle gun.  This allows you to alter the spray and texture achieved, so I will experiment with that as well.  I have also seen that some people buy a $10 harbor freight hvlp gun and drill it out to 2mm - this can produce an even finer finish.  Depending on how my experiments go, I may buy that and experiment with it as well.

I think I am getting close to the time to spray the undercoat.  I want to put the last of the primer coats on the body so I don't have to tape up/cover the bottom of the car.  I don't want to get primer over spray on the undercoat.  However, I do want to get paint over spray on the undercoat - hopefully just like the factory!  I will need to work with the painter to get that close, hopefully.  Basically, it looks like that involves painting most of the wheel wells, front and rear.  And, hitting the floor pretty good along the outer sides... and blending toward the center.  I will attempt to replicate the over spray on the spare tire well too.  

Part of me wants to paint the bottom of the car like the Franklin Mint 240z, but I will try to be more faithful to the original look.

Garrett