Hot Rods What Is This Undercoat Type??

So i've ran across this before on some of the old 50's 60's vehicles I've owned. The undercoating? It basically looks like hardened tar & asphalt and is real thick. My question is what exactly is it?
I'm working on my lil 50 Crosley and it's on it and i'm pretty sure they used it to help the sheet metal rigid and from sounding tinny.

I had to remove most to do repairs and that but looking to put something like that back on it.

 

I've heard it called "tack".

 

Hello,
Right after my brother bought his new black 58 Impala, he was told by our dad’s mechanic friend to bring it up to LA for some extra stuff. He gave us a two cases of oil, a case of STP and Wynn’s Friction Proofing and some high performance spark plugs we had never heard of before. That was the best surprise present for a couple of teenagers.

But, the topper was that he had our Impala cleaned underneath, and dried while we were talking. I did not know why he had that service done. To the bottom of a car? Why? No one looks underneath and the road grime will cover it within a month or two.

We were told to drive over to this small shop in an industrial area near the downtown location and talk to the owner. It was explained to us that this other shop was going to spray a thick coat of black undercoat on all surfaces of the Impala. It came painted black from the factory, but it was just a mild coat of paint and not on absolutely all surfaces. The extra sprayed on undercoating would help protect the metal surfaces that the factory spray did not cover. There were quite a few areas left in bare metal surfaces by the factory.

So, upon arriving, the Impala was put on a lift rack and a coat of something was sprayed on first. After that dried, the owner proceeded to spray on this very thick rubbery, black stuff that had an awful smell. Something to the equivalent of standing in the middle of a Signal Hill Oil Field all day. He coated all of the surfaces with this thick coating while we were watching from afar.

It was something we did not want to do at any time, but it was a necessary item. Our friend, the mechanic, told us that if we were going to the beach and mountains all of the time, the moisture will advance the rust process quickly. This “stuff” was going to prevent that as well as give us some sound barrier from road and exhaust noise.

Jnaki

It did take a while to spray on the black gooey stuff and let it dry. But, we were patient. When we hit the road back to our house, we had to drive with all of the windows down on the roadways. We were told that it would smell for a week or so, but not to wash it with a spray hose until the following month. Who washes the underneath surfaces? We thanked the owner and took off down the road.

When we did take the Impala to the beach, rolled through some standing salt water, dirt and other things, it was a feeling of satisfaction that nothing was attacking the metal surfaces. If it looked awful, a powerful spray wash at the local $.25 cent car wash would not damage the undercoating. It worked well for the sound coming from the exhaust, too. Even when we put in the tube Corvette Mufflers, the sound was pleasant and still good for road trip conversations, in the front and back seats.

In the fall of 1964, I sold my two favorite teenage hot rods. My 1940 Flathead powered Ford Sedan Delivery went to a surfer from Huntington Beach and my 58 Impala stayed in Long Beach with one of my friends. So, I had a new 1965 El Camino that came from the dealer with nothing on the bottom, except for some factory paint. It was not on all surfaces and I could see bare metal, too. So, I called the owner of the undercoating shop in LA and he remembered our 58 Impala from back in his early days.

On my El Camino, he sprayed every surface underneath and wondered why the factory did not spray anything on those metal surfaces. The El Camino provided plenty of noise with the empty bed or even with the bed full of beach stuff, surfboards and/or two motorcycles. As soon as the owner of the undercoating shop sprayed on his thick black stuff, the noise was lowered to almost nil, the sound of the mufflers was a little better and I still had to roll down the windows on the drive home. It was really bad in the smell department.

But, over 125k miles later, the bottom, after a good power spray cleaning, looked really good for a 12 year old El Camino that was driven all over So Cal and into Mexico. There were many times on our frequent surf road trips going through high tide, standing salt water. But, there were also a couple of South of the Border, beachfront motorcycle races in the sand/water and dirt cliff areas, too. All of the road grime was easily sprayed off with a power wash sprayer. The undercoating was a lifesaver and kept the El Camino pristine for all of those fun, road trip, cruising miles. Dirt and salt? ...not a problem...