Underside of the car...undercoat or no undercoat???

[Lord Warlock]

When you look at these full body restoration cars, especially ones at BJ, you see the entire underbody has been stripped clean and repainted the body color, which I'll admit looks so much nicer than a full undercoat layer underneath.  But when I get under my car and look at the underside of the trunk area, floor pan and inner fenders, my car is thoroughly coated in undercoating.  Now I remember using spray on undercoat on parts of the inner front fenders when i was 18 or so, but only because it was everywhere else.  It all looks uniform and is complete.  I'd like to believe that this coating has been a help in keeping the rust to a minimum.  The only rust my car has is along the rear sail panel/back window on the left side (while standing behind the car facing the trunk) and some minor pinholing in the rear quarter trunk extensions, and some of the trunk drain holes have aren't perfectly round anymore.  The spare tire mount is a bit rusty too-but the trunk floor is still solid as a rock. 

What was the factory undercoating like?  In what areas? and why do you see so many cars with no undercoat if the car was coated originally?  I understand cars that are sandblasted or stripped/dipped and the surface is clear already, but seeing as my underbody is very solid already, and blasting it clean of undercoat would probably just weaken the surface of the metal, it doesn't make sense to strip it all off unless it is somehow allowing moisture to stay on the panel rather than keep it off (such as water on the inside getting under the coating) The brake wires and rear differential don't appear to have any undercoating on them, which would be the case if it was sprayed on aftermarket.  I have to assume it was done from the factory this way. 

Is there a danger to leave the undercoating on?  Is it removed for a good reason?  To remain faithful to being stock, i'd rather leave it in place...which makes the restore process somewhat easier if i don't have to strip the bottom of the car too.  (no rotisserie or sand blaster) I do think I will have to strip off the fiberglass mat/resin that i used on the inside of the trunk 15 years ago, when i was worried about future rustout, and do a complete grind/buff/seal and repaint of the inner trunk area.  I already did that to the passenger area of the car under the seats and floorpan.  I just feel the fiberglass doesn't look as clean now as it did way back when i did it, and nowadays I think i can do a much better job on it. 

Lord Warlock

[moparguy01]

what i would do is get a needle scaler and use it to just knock off anything that loose. then spray a new layer of undercoating on it if you want to stay original. I've never seen an original car with a nice painted undercarriage. those ones are all over restored.

the original undercoat looks to be close to roofing tar thinned with lacquer thinner. I know it probably was different but thats sure what it reminds me of.

[Judhudson]

I was planning on scraping or blasting it all off then putting new undercoating on.

[41husk]

on my Challenger, I stripped it primmed and painted it then went over that with undercoating,  Thats the way mine had alway looked,  you could see the body color comming through in some spots that had not been hit well with undercoating, I tried to make it look just like that.  Not sure I like it though

[Charger-Bodie]

if you have a nice clean underbody area i would go body color its not always over restored as much as it is just more detail imo and it looks so good when done right ....you can always reundercoat it later alot of cars that are reundercoated have somrthing to hide not all but alot of them

[Just 6T9 CHGR]

Looking at your broadcast sheet your car was not coded J55 for hood pad & undercoating.   If you are doing an "as built" resto , I'd leave it off...

Heres a great refrence site for factory undercoating application areas on a B body

http://www.hoffmanswinnerscircle.com/69rtconvertible/index.htm

[Blakcharger440]

The undercoating is exactly what protected these cars in the first place. If you are planning to drive the car at all I would put undercoating back on it for protection.
Alot of cars that did not get undercoated from the factory rusted out earlier than those that did not.

[Lord Warlock]

I don't have a hood insulator on the car, never saw one since i first got it so don't anticipate adding one in the future, the undercoating though is applied pretty much in the same areas shown in the link supplied.  Is it uncommon to have undercoating where it isn't coded on the car?  There is just too much on the car to believe that it was applied aftermarket, and being a car on the seacoast (either Mobile Alabama or Pensacola Fl) sea salt is always something to worry about.  So I can see where an owner may have had the dealer do it. 

As for the current restoration, I'm pretty much focusing on whats visible or accessible.  I'll deal with the undercarriage after I can afford to install a lift in the garage, (not eager to spend months rolling around on a creeper in mid winter-that concrete is cold).  My main concern with this thread was to find out why some cars have totally clean undercarriages as shown in restorations.  I know that if i had mine blasted clean, I'd probably go with repainting the undercarriage to match the body color, as you can see some body color in places underneath but not much.  Mine just appears to have had a thorough undercoating job done to it, well beyond what someone would have been able to do with cans of spray on coatings...it would have taken 20 cans or more to coat the entire underbody as mine looks, plus there are areas under the car that someone with a can would not have been able to get to, much less coat evenly.

I seem to be missing a couple of the access plate covers in the inner front fenders, (nice looking superbee in the link by the way-great color).  I'll have to try and locate them in the future.

[Lord Warlock]

What is the best way to remove undercoating? is there a solvent that dissolves it or loosens it?  Chiseling it off by hand would be way too complicated, plus it would probably damage the metal underneath.  Sandblasting would do it, but it would take a lot of sand to do it right.  Plus I'd have to remove everything from under the car before having it done.  I anticipate getting a new blaster in the future, the old gravity feed hopper i have pretty much sucks, and doesn't work well on large areas, just small parts.  Don't think my small compressor could handle it anyway, figure i'll upgrade the compressor to a much larger system when funds permit. 

[41husk]

I used a DA, but you will need a pretty good compressor to push it.

[sean68charger]

you get a lot more protection from undercoat if you intend to use the car as it should be and not a trailer queen

[bull]

I've been told by many that undercoating cannot be blasted off. It has to be heated up and scraped off -- a very time-consuming process.

Mine has factory undercoating and the only thing I don't like about it is that it's dirty. Road grime has gotten stuck to the undercoating and it just looks dirty so I need to figure out a way to clean it someday. Maybe I'll pressure wash it once it's all restored. Also, some of it is coming off in spots but I plan on leaving it on and scraping/adding to those areas with spray can undercoating. I would like having it painted underneath but it's not that big of an issue to me so I can't see going through all the time, effort and money it would take to do it right.

In answer to another of your questions, I don't see many of these cars being driven in bad weather enough these days to where undercoating is really going to prevent that much corrosion.

[Lord Warlock]

I imagine i'll end up pressure washing mine to get road grime off and afterwards paint it black so it doesn't show up so much.  The hard part is getting the stupid pressure washing wand in a position where it will do any good under the car, my wand is 4 feet long.  If it shows signs of flaking off under the trunk area, i'd like to take it off there at least, and have a clean paint job, but in the wheelwells i'd rather have the undercoating there. 

If it can't be blasted off, mine will just have to remain coated, i don't have the patience to scrape every square inch then sand it manually to clean it to the surface, then prime and paint it just to make it look shiny under the car.  I have no problem in primer and painting it, and plan on doing that myself anyway, but just sanding the visible surfaces is enough work, as is wetsanding and buffing new paint out.  (in the surface prep and primer phase right now)

LW

[472 R/T SE]

bull, Bill has a pretty close match for factory undercoating per Tom.  He's even pretty accurate at applying it per factory procedures per Tom.

Lord, the only way I've heard of getting it off is with a little hand held butane or propane? bottle and a scraper.  Then paint thinner to clean it up.

I've tried to shoot gloss black over it to shine it up with no luck.  The best thing I've found to spruce it up is use vinyl shine on it.    But that only lasts so long before it's all dull again.

[Lord Warlock]

Maybe when i drop the gas tank the next time, (need to drain some bad gas out of it anyway) I'll take the butane torch to the areas surrounding the area under the tank to see if it cleans up.  I have the torch and scrapers already.   The pictures of the undercoating in the link look very much like the coating found inside the trunk and inner doors, the undercoating under the car looks a bit heavier on mine than what the shots on the superbee.  Its supposed to be warmer tomorrow, so maybe i can do a bit of crawling around with the digital camera.  I can't depend on the fenderwells looking the same since I know i've used can undercoat on the inside of some of the inner fenders. 

[ChargerSG]

I did pressure wash mine, got all the loose stuff and dirt off and them after been drying for awaile put new coating on, i wanted to keep as much stock as possible

[Charger-Bodie]

we sand blast every rotiserie resto shell inside and out on the floors and gine compartment with a rented construction compressor and a rented blaster that holds 600lbs of sand it works awesome i highly recomend doing so and paint on the underside the detail looks very good by the way with the outfit we use it only takes about 5 hours to do it inc some misc parts cuchas k frame ect but just dont use any sand blaster on the main body panel or they will worp

[Lord Warlock]

chargerSG:  nice looking mustang projects you have there on your website.  I had a convertible 289 4spd stang the same color as your bronze colored one.  Drove it for a year before i bought my charger.  We sold it for almost 6k back in the late 70s, even though the floors needed new pans, (we found a yield street sign welded in place when cutting out the rust)

As much as I'd like to strip the charger down to the bare shell and have it blasted clean, and repainted the right way on a rotisserie, it just isn't likely due to limited storage space and funds.  I've inquired several shops to get an idea of what it would cost to have it done and noone really answers the question.  After spending 25k rebuilding a turbo stealth, i now regret doing so and would have preferred to have spent the cash on the charger instead (it was my daily driver at the time).  Maybe if I win the lotto or get a major windfall sometime, I'll be able to send the charger out for a real restoration.  I've already stripped the outer body to bare metal, as well as the passenger area, and ground out all the minor surface rust, then sealed and treated the good metal and reprimered the parts.  The only part I'd prefer to have cut out and replaced is the sail panel, which rusted along the window channel about 4 inches x 1 inch along the lip.  But i've already ground/cut out the rusted area and rebuilt it with Por15 epoxy putty, (gonna have to sand it smooth inside the trunk to finish it out-was just in there last week and noticed the appearance inside the trunk area). 

The underside just looks extraordinarily dusty/dirty after sitting in storage for so long.  I'd like to clean it so it looked black again, because it is just dust colored now.  but stripping the inner fenders of undercoat isn't likely, the undercarriage is a different story.  I'd like it to look as clean as the rest of the body once the paint is finished.  But that will involve removal of the exhaust system, driveshaft and likely the leaf springs and axle, which is all major work without a lift or rotisserie to get it turned up where all the niches are within reach.  I plan on getting a lift in the future, the garage was built with a lift in mind (height and wiring).     

[dongar69]

If you want the detail underneath but also some rust protection, try sem undercoating.
It can be tinted with body color to match. spray it on thick or thin,smooth or rough.
Quite a bit of options when using that stuf.

[JimShine]

I found that Tal Strip loosens up the factory undercoating.

It is great to read positive comments about undercoating here. It has been a myth for so long that it trapped in moisture and rotted cars. But rotted cars I have seen with it always rotted from the inside out from leaks, clogged drail holes, and wet feet.

[bull]

bull, Bill has a pretty close match for factory undercoating per Tom.  He's even pretty accurate at applying it per factory procedures per Tom.

Cool. I'll have to ask him about that... if I ever get the money to finish my car.

[Lord Warlock]

I found that Tal Strip loosens up the factory undercoating

Hmmm may have to test this out.... have a half gallon of it left over from stripping the paint.

If you want the detail underneath but also some rust protection, try sem undercoating

Thanks,  I didn't know that SEM sold an undercoat product.  I'll check into that.  I've used SEM vinyl dye before and like their products. 

[daytonalo]

THAT SEM UNDERCOATING , DOES IT COME IN A GALLON AND USE A SHUZT GUN OR IS IT IN A CAN ?

[resq302]

I know when I was growing up my grandfather always told me that a selling point for a salesman was to throw in the dealer applied undercoating as this helped protect the car.  My charger must have had this as the undercoating is up to 1/2" thick in some areas under the car and hardly any at all in some others.  He used to tell me stories of how he got a car from the dealership and it started smoking from the undercarriage.  Turns out the brainiak tech person got undercoating all over the exhaust too.

[JimShine]

When you Tal Strip it, apply it heavy, and reapply as it dries. Give it a half hour or so to work its way in and it will soften up a bit. It depends on how thick it is, but heavy layers may need a few applications to get it down.