Undercoating Questions

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MrSony

Geezer
Nov 15, 2014
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Des Moines, Iowa
1. What are the steps for application? Primer paint unsercoating? No paint? No primer?

2. Any discernable difference between bed liner and undercoating?
 

Clone TIE Pilot

Comic Book Super Hero
Aug 14, 2011
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Galaxy far far away
Paint protects the metal, undercoating protects the paint.
 
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UC645

Royal Smart Person
Apr 20, 2020
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I’d at least go with some oil based enamel first, then an oil based undercoating. Rust treatment where applicable.

I wouldn’t dare think of using bed liner on the underside of any car, even if its rubberized, it just lays on whatever surface you put it on and will trap water if done improperly. Don’t ever use a hard type undercoating if you drive it in the winter. There’s a reason the cars up north that used oil instead of a hardening type of undercoating are still factory new in some cases.
 
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mikester

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Mar 10, 2010
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We all have opinions. I used 3M Body Schutz on both of my cars. The only reason that I did is I used it since the 90s on multiple 4x4 projects and on my 72 Nova.
Would I use it again ? Nope. Theres so many better products made now and I just didnt know it at the time.
A friend of mine has a body shop. He does one or two vehicles at a time. Body off rebuilds. If the customer doesnt specify a painted bottom he uses U-Pol Raptor. The stuff looks great. Sprays out even and you can tint it. If I could do it all over again it would be on both of my cars.
As far as moisture getting under it, neither one of my cars will ever see rain or snow so I think it would have held up well. Again, just my opinion.

BTW, I dont think there are many long lasting enamels made these days. The VOC regs took all the good (bad) chemicals out of them. I would use a good automotive epoxy primer. I usually use PPG DP40 but Im sure theres others even better and cheaper. The supplier I use sells mostly PPG so thats what Ive been using.
 
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fleming442

Captain Tenneal
Dec 26, 2013
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I'm interested in this subject as well for my 78. Why would moisture get under the bed liner anymore than it would with paint? I have heard that the spray-on traditional undercoat is porous, and will transfer moisture, aside from just flat wearing off (personal observation). I like the ideas of the bedliner being waterproof and noise reducing.
 
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UC645

Royal Smart Person
Apr 20, 2020
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Kittanning, Pa
I'm interested in this subject as well for my 78. Why would moisture get under the bed liner anymore than it would with paint? I have heard that the spray-on traditional undercoat is porous, and will transfer moisture, aside from just flat wearing off (personal observation). I like the ideas of the bedliner being waterproof and noise reducing.
The only reason I’m against it is both my former and current dailies had the cheap spray can stuff on the frame and on the body with my current one.
My 90 S10 had really bad rust underneath because none of the stuff had adhered properly. Ive got a 99 Silverado now, it had rattle can stuff up to the main body line, had a couple of cuts in it near the front of the doors, there were holes the size of my fist behind those cuts.

If you have a reputable shop do it, it’ll be fine.
 

mikester

Comic Book Super Hero
Mar 10, 2010
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Small town NY
I'm interested in this subject as well for my 78. Why would moisture get under the bed liner anymore than it would with paint? I have heard that the spray-on traditional undercoat is porous, and will transfer moisture, aside from just flat wearing off (personal observation). I like the ideas of the bedliner being waterproof and noise reducing.
I had bedliner sprayed in my 2011 GMC. It held up very well. Snow, rain, nothing got underneath it and that was sitting on top for extended periods. In my opinion I cant see water getting up under it on the bottom of a vehicle seldom used.
 
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Clone TIE Pilot

Comic Book Super Hero
Aug 14, 2011
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Galaxy far far away
I'm interested in this subject as well for my 78. Why would moisture get under the bed liner anymore than it would with paint? I have heard that the spray-on traditional undercoat is porous, and will transfer moisture, aside from just flat wearing off (personal observation). I like the ideas of the bedliner being waterproof and noise reducing.

If you don't get the surface completely dry before applying bedliner, it can can trap dew from the air. By dry I mean a indoor moisture controlled shop and running heated air dryers at the surface for hours. My Regal was factory undercoated and its cleaner than most G bodies. As I said, undercoating does not protect metal, it protects the paint that protects the metal. The waxy undercoating like Fluid Film is better than the old rubber undercoating which is what I applied on my CVPI. With either type, you will want a undercoating gun and stay away from aerosol cans.
 
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