Undercoating. Was it ever done at the factory?

[MarcDeSoto]

I've read that undercoating a car back in the 40s and 50s was an extra performed by the dealer.  But my 48 DeSoto was so thoroughly undercoated that I believe it was undercoated at the factory.  Why?  Because I don't think a dealer would have gone to all the trouble of removing the seat and the carpeting and mats to undercoat the floor from the front all the way to the back of the trunk, as well as the entire undercarriage.  what are your opinions?  

[sidevalvepete]

Perhaps the "undercoating" referred to in your reading really meant an undersealing or anti rust coating applied under the car ? Pretty sure they were all undercorated in the paint process.

Edited February 19, 2021 by sidevalvepete

[Eneto-55]

By undercarriage, do you mean the frame as well?  I of course don't know, but I would assume that if it were done in the factory itself, it would have been done prior to setting the body on the frame.  But to your point - my 46 (an Oklahoma car until I brought out here to Ohio 2 1/2 years ago) was not undercoated, neither underneath nor inside, on the floor or trunk.  I did it myself in 1980, with a special gun my Dad borrowed from the Olds dealership where he worked.  So even then, (at least at Olds) undercoating was an optional thing generally done by the dealer.  However, it might be that if someone ordered their car instead of taking one already on the new car lot, they might have done it during the manufacturing process.  (So here I am arguing with myself....)  

[MarcDeSoto]

Good questions Eneto.  Yes, everything under the car is undercoated with a thick asphalt like undercoating including the frame.  By undercoating, I'm not talking about a paint like anti rust coating, but thick asphalt or whatever it is.  The fenders and hood also were undercoated.  So this car rust wise is a restorer's dream!  Parts of it, like on the trunk floor got very dry over the years and cracked in chunks allowing some surface rust to form there, but no thick rust.  I've already taken care to the trunk floor surface rust.  Only the front section of the frame in the engine compartment is not undercoated.  

Edited February 19, 2021 by MarcDeSoto

[Eneto-55]

The stuff I used on my car would not be my choice now - way more options, and probably better materials now.  I can't remember the ingredients, but it was, as you say, some sort of tar-based stuff.  It came in quart cans which screwed right onto the air gun.  It was a simple siphon feed affair that basically just spit the stuff on.  I coated both the underside and the floor inside.  I painted over it with enamel paint on the inside, but just left it as it was underneath.  I had also sprayed the rear wheel wells (not inside the fenders themselves, as I wasn't finished reshaping them yet), and sprayed the body color lacquer over that area, but it really checked, or cracked.

I haven't tried it myself, but I've heard that that stuff in a spray can that freezes stuff works well if you need to get it off.  You freeze a section, then hit it with a hammer, and the tar just shatters.  

If I were doing it now, I would probably use that rock guard spray, or something similar.

Edited February 19, 2021 by Eneto-55

[plymouthcranbrook]

My 52 had(has still in spots) a heavy thick asphalt type coating but just on the underside of the car body.  Frame did not have any. I scraped off as much as I could 17 years ago when I sprayed the entire underside with POR 15.   

[Marcel Backs]

My 40 D14 also had lots of 80 yr old fossilized tar among other nasty substances that accumulated over the decades. The removal of this stuff can be one of the most tedious and dirty jobs in the cleanup process. The majority of it was at the inner rear fenders and the rear undercarriage.  A bit was encountered  towards the front and it ended at the cowl. What worked for me in the removal of this was heating (using a propane torch) and scraping ( with a gasket scraper) as much of this crap off as possible which is a long process to say the least. I would put a sheet of plastic under the car because you do not want any of this junk on your shop floor. For the next part I rolled the frame and body outside and repeatedly washed down the tarry areas with gun wash soaked rags which is pretty nasty but effective albeit time consuming. Make sure you are outdoors on a windy day when using solvent and keep a fire extinguisher close by. This will eventually leave you with a surface that you can finally degrease and prep for paint. So far this was the task I spent the most time on and liked the least in the restoration process. M

[desoto1939]

I know a lot of cars in the late 50-60 had spray on rust ont he underside of the car and frame.

 

They did find out over the years and later on that this antirust process actually caused more rot out becasue when a stone or large object het the bottom of the car it would chip away at the material and then make a small hole int he coating.  So when it rained or snow with rock salt on the roadways the melted water with the salt brine would get into the small hole and then get behind the antirust coating and then start the rusting process.

 

The car owners never knew this was happening and then one day thy see a rust spot.  I am surprised that someone did the interior along with the inside of the hood and other areas.  I would also assume that the surface is not smooth but of a rough texture.  This is going to be hard to get off the metal and might have to be blasted with sand or some other material to remove it.

 

 

Thy have also found that when the plastic truck bed liners have been installed that the water gets underneath the liner and then starts to rust out the pickup bed and rusting occur also at the fenders.

Also as a safety issue,  When you have a plastic bed liner NEVER fill a gas can with gas while the gas can is still in the pickup bed area.  The car and the liner can cause static electricity and then when the can is opened and the nozzle is placed in t e gas can the gas fumes and the static causes a spark and then you have a MAJOR Explosion.  I worked in a Gas  station and have first hand experience of seeing this happen.  SO ALWAYS REMOVE THE GAS CAN FROM THE CAR OR TRUCK WHEN FILLING THE GAS CAN.  THES SAME WARNINGS ARE POSTED ONTHE PUMPS.  I HAVE SEEN OTHER PEOPLE NOT TAKE THE CAN OUTOF THE BED AND WHEN I SEE THIS I INFORM THEM OF THE POTENTIAL DANGER AND THEN SHOW THEM THE WARNING LABEL ON THE GAS PUMP.  BOY ARE THEY TAKEN BACK BY THAT INFORMATION.

 

I do know that on my 39 Desoto the underside of the hood and the side engine compartment panels were not painted the color of the car which was Steamliner gray. These panels had a very dark green black primer coating and the paint was a smooth finish.  I think this was a base under coating or primer.  This was a one owner car so I do not think anyone resprayed this area.

 

Just some more information on undercoating.

 

Rich Hartung

desoto1939@aol.com

[Bob Riding]

Timely, as I was just researching which undercoating to spray on my '52 Suburban. It too has a thick coating of asphalt-like stuff in various stages of decay. Some areas are very solid and others more flaky. I've scraped the loose stuff, sprayed primer/paint to stop further rust, but now I'm wondering what to spray in the thin areas. Being in CA I'm not worried about trapping salted road slush/water, but for dent protection from road debris and soundproofing. Flex Seal, Rustoleum...CRC?

[Marcel Backs]

To finish the undercarriage once cleaned of a good 35 pounds of undercoating, gear lube, desert sand, motor oil, etc. the wire brushes (many) on the end of the drill part of the process starts. This is also a time consuming task that requires a few beer breaks because of it's sheer tedious nature. I did this for the complete frame and underbody sections while they were separated accessing 99 % of the areas ridding them of any thick scaly bits. You basically keep this up until the surfaces are well roughed up having exposed metal and some areas with a bit of rust which could not be removed short of sandblasting. A this point the two sections are ready for degreasing ( I recommend KBS coatings Aqua Kleen NAPA has it here). I would seriously consider their Rust Blast and Rust Seal products for final finish with excellent results and rust completely arrested. This was all done at home. I ended up nicknaming my ride Old Filthy as a result! M

****REMEMBER chances are during the stripping process you will encounter original body paints and primers THESE ARE LEAD BASED!  and as well as being really hard to strip they make it necessary to wear a good quality filter mask. 

Edited February 21, 2021 by Marcel Backs
more info on old paint and primer

[James_Douglas]

The underside of my 1947 Desoto Suburban was coated with a heavy coating. So was the underside of the hood. The car never saw a salt road. It is thick, but it is not "tar". It comes off in hunks.  It appears to have been done at the factory.

 

James.

[Bob Riding]

I have a Chrysler '54 Town and Country wagon like that. I think probably factory applied as it is everywhere on the sheet metal panels, but not the mechanical bits. Sound deadening, most likely.

[DJ194950]

My 1950 Suburban wagon had a lot of heavy undercoating in lots of areas.

 

I found out quickly that sandblast did almost nothing to it but stick into it. If overdone it warps panels which is Bad!

 

Aircraft paint remover will soften it to a heavy tar like that can then be scrapped off with some effort. Where real heavy a second or third coating may be required but was by far the easiest in my experience.  Also make sure to catch the mess on disposable paper, cardboard, etc. It is very sticky!

It seems to be available at most auto paint stores and I believe that Summit Racing also sells this. Buy a gallon as it needs to applied fairly heavy which the only size container I ever saw, but??

 

DJ

[Eneto-55]

23 minutes ago, DJ194950 said:

My 1950 Suburban wagon had a lot of heavy undercoating in lots of areas.

 

I found out quickly that sandblast did almost nothing to it but stick into it. If overdone it warps panels which is Bad!

 

Aircraft paint remover will soften it to a heavy tar like that can then be scrapped off with some effort. Where real heavy a second or third coating may be required but was by far the easiest in my experience.  Also make sure to catch the mess on disposable paper, cardboard, etc. It is very sticky!

It seems to be available at most auto paint stores and I believe that Summit Racing also sells this. Buy a gallon as it needs to applied fairly heavy which the only size container I ever saw, but??

 

DJ

As I said above, mine didn't have any before I sprayed it on myself.  The gun I used produced a pretty thin uniform coating.  As to whether it was a good idea or not - that I don't know.,  I've seen those statements about water getting under it before, but I think that it may be that the 'rock guard' that came out later may be worse for that.  It was 1980 technology, and I was rebuilding my car as a daily driver (as they call it now).  

But as to getting old undercoating off, if I was doing that, I would try the freeze and smack approach.  Maybe do it on a really cold day in the winter (if you live it the "freezer belt" like I do now), and then use that freeze spray.  (Plumbers apparently use it too, to stop water flow temporarily while doing a pipe repair.)  That way it's not sticky, and also beings it's cold weather, you can be covered head to toe w/o getting hot.  I think my brother told me about that method, and I kinda' think that's how he got it off of his 66 Charger. As for solvents, I get pretty sick right away with fumes from stuff like Xylene, which I would imagine would also work, as far as softening it up goes.

[T120]

May be of interest....Bonderizing for rust prevention. I believe all manufacturers now use rust proofing on body sheet metal... This is from  a 1947 Nash brochure.

 

 

[allbizz49]

If you are trying to remove old, hard stuck on undercoating, take a torch, like a small propane one, and heat up a scraper or putty knife. Scrapes it right of. It's messy and nasty but this is the best method I have found doing 100% nut and bolt restos.

[Dodgeb4ya]

My higher end 1950 Chrysler's ...

( NewYorker/Town and Country) came from the factory with the super thick sound deadener on the underside of the floor pan....none at all on the frame or gas tank.

It's also found inside of the doors and 1/4 panels...also on the underside of the trunk lid and on the floor.

It makes a huge difference in the noise level inside of the car.

Edited February 21, 2021 by Dodgeb4ya

[Bob Riding]

Exactly my experience with my 54 Town & Country. So how do we duplicate this material? It’s worked well all these years and kept the rust out too. Any current spray products that we could substitute?

[Bob Riding]

On 2/20/2021 at 1:50 PM, T120 said:

May be of interest....Bonderizing for rust prevention. I believe all manufacturers now use rust proofing on body sheet metal... This is from  a 1947 Nash brochure.

 

 

Love those 40's advertising terms - "Bonderizing", "Sand-Mortex", "Hi-test safety glass", "Super hydraulic brakes", "Automatic overtake", "silent -ribbed tires", and of course "Deluxe" everything!. Although this is from Nash, mother Mopar was no stranger to creating marketing jargon that sounded impressive, rocket-age, but was probably not that much different form other automakers products.

[52b3b Joe]

Our 48 Desoto has it on the underside of the body, on the back side of the fenders, and under the hood. The frame does not have it. It's tough stuff to remove if needed. My only complaint with it is the use of it on the hood. It is heavy and the hood springs struggle to keep the hood up with the added weight. 

[Marcel Backs]

I have been thinking of using un-sanded truck bed liner on the inside of my fenders. It could help protect the sheetmetal from stones bouncing up from the wheels. I used some on the inside of my trunk and it closely resembles the old bitumen undercoating.

[Bob Riding]

37 minutes ago, Marcel Backs said:

I have been thinking of using un-sanded truck bed liner on the inside of my fenders. It could help protect the sheetmetal from stones bouncing up from the wheels. I used some on the inside of my trunk and it closely resembles the old bitumen undercoating.

Good idea! I just ordered the Herculiner Truck bed coating. I will report out on my results.

[plymouthcranbrook]

6 hours ago, Bob Riding said:

Love those 40's advertising terms - "Bonderizing", "Sand-Mortex", "Hi-test safety glass", "Super hydraulic brakes", "Automatic overtake", "silent -ribbed tires", and of course "Deluxe" everything!. Although this is from Nash, mother Mopar was no stranger to creating marketing jargon that sounded impressive, rocket-age, but was probably not that much different form other automakers products.

Back in the days when “Truth in Advertising” laws were not so strongly enforced.  And a nation not quite so sue happy

[plymouthcranbrook]

Regarding the undercoating I scraped off what came off somewhat easily and after cleaning just sprayed POR 15 over the top and inside the frame rails. Inside the door I just used spray cans(several)of rubberized undercoating. 

[allbizz49]

Best undercoating I've used is Dynatron from a gun. The texture is controllable and dries fully. Also, if you want something good for fenderwells or painted areas, try 3m rocker schutz. Also from a gun. The guns you use screw onto the cans so it's pretty simple to use and easy to clean up.