Undercoating, my two cents too

[mwl1967@xxxx]

Ben,

Decide first why you want to either remove or keep the 
undercoating. It was never meant as a rust preventative nor is it likely that 
your restored E is ever going to see salt , slush and snow anyway. A good 
epoxy primer by itself will do more to prevent rust than any undercoating 
job. 

If you're doing a frame off, rotisserie job and plan to display 
the car with mirrors underneath and want it to look pretty then remove it 
all, and paint the underside of the car. To maintain some flavor of 
authenticity however I don't recommend fully painting the floorpans, rather 
overspray from the sides, shooting towards the center of the vehicle and 
don't paint into the trans tunnel or in the area above the rear axle housing. 
I believe undercoating was standard on all 300's but not sure, perhaps 
someone else can confirm this but if you want mirrors and looks leave it off 
but remember its probably not original.

If you're doing the rotisserie style job and want to remove the 
old undercoating with the intention of repainting the floor pans and putting 
the undercoating back for originality then I'd advise against it for several 
reasons.

1. done properly its extremely time consuming and if you're not doing it 
yourself figure on 30-40 hours or more of prep time before its ready 
for paint, ie: $$$

2. you'll have an extremely hard time trying to duplicate the look and 
also texture of 
the original undercoating. That stuff was blown on at pressure and a 
spray can 
isn't going to cut it. Personal experience with a pressurized 
applicator gun you 
can buy at an auto paint supply house wont give you the same results 
either.

3. Unless the stuff is cracking and loose (too late, you've probably got 
rust), leave
it alone, you wont find any rust underneath it unless your car is 
rotten from the
inside out and then its likely that the undercoating is all that's 
keeping your 
carpet in the car. 

If you want undercoating consider this... Carefully inspect the 
underside and remove any loose undercoating. Make all your metal repairs and 
refinish the underside of the vehicle as ORIGINAL where appropriate. Apply 
body color underneath where you find it and leave anything bare primer and 
not painted nor undercoated ... as you find it appropriate. A mixture of PPG 
DP90 and DP40 epoxy primers will resemble the grayish Chrysler primer and it 
wont rust through. Now that the metal underside of the vehicle has been 
painted and/or primered like the day it was assembled 40 something years ago 
you can repair the undercoat where needed per John Hertog's recommendation. 
Finally, avoid "rubberized" undercoating in a can and find a brand called 
Dynatron. Get a few cans and lightly coat the original existing 
undercoating. This will simply give a like-new coloring to your old 
undercoat while also "blending" any repaired undercoat and it will also cover 
any overspray of primers or body colors which will have gotten on the 
original undercoating as you were spraying the bottom of the car. 

While the above is only my recommendations based on my results using 
several different techniques on several different cars I've done I hope it 
will at least give you some more options to consider. I'd also recommend not 
only carefully photographing your car's existing details for documentation 
but also seeking out the advice of one of the club's knowledgeable 
undercarriage judges. Good luck!

Michael Laiserin
Phoenix, Az