Rubberized Undercoating vs bed liner

[E5 Charger]

I have my 74 on a rotisserie and am close to getting the underbody to bare metal. I plan to paint it and then cover the entire bottom with rubberized undercoating or Raptor Bed Liner. Should I use seam sealer on the panel joints? It didn't look like the factory used any on the bottom, just on the inside. What are the pro's and cons of undercoating vs bed liner.

[JR]

The key difference between the two is, undercoating is typically sold as "self-repairing". Meaning if you scratch it, the undercoating around the scratch will flow back and cover the scratch, sealing the metal. A downside is, undercoating has no UV resistance usually. And sunlight exposure will turn it a dull brown eventually. (Probably take a long time if you keep your car indoors though.) The gun typically doesn't require a very big compressor to spray it, a 20 gallon one should work fine.

Truck bed liner is typically rock hard when sprayed, and doesn't self repair. But is incredibly tough and very hard to scratch. Truck bed liner also has UV resistance, and will look "fresh" longer. The only catch is, if you're going to spray this yourself, you need a big compressor. The spray gun for bed liner needs alot of volume to spray properly. A full sized, compressor is necessary here. (We used a 60 gallon at my shop, and the compressor would kick on two or three times just spraying a six foot truck bed.)


I used to spray truck bed liners for a day job, and did a bunch of floors for restorations like your doing. I never had a comeback, or saw any downsides to the truck bed liner. So it's really a matter of preference.

For what it's worth, I used U-POL undercoating on my stuff. It's much cheaper than the bedliner, self repairs, and is easy to spray. Although I do have to hit the wheel wells with black spray paint every couple of years to keep them a deep black.

Also, I'd be hesitant to use seam sealer underneath the car because when water inevitably finds its way trapped between the sealer and the floor, it will rot out the steel from the inside. I'm guessing that's why the factory never used any underneath.

The primer/paint/undercoating or bedliner should be plenty of protection underneath.

[E5 Charger]

Thanks, great explanation. Do you think seam sealer on the joints is necessary? How large of a compressor? I have a single cylinder, 5.5 HP, 25 gallon, that says 7.8 scfm at 40 psi. Will this work? I'm assuming the compressor size would be the same for undercoating. Where did you buy your U-POL undercoating? I don't see it on their website.

[JR]

I edited my original post with some of the details before I saw that you had responded.

That compressor should be fine for undercoating. I sprayed my undercoating at my home garage with a 20 gallon compressor, that shouldnt be a problem.

If you go with truck bed liner, I'd expect to have to wait and let the compressor catch up alot, but it can technically spray it.

Maybe the new bedliner spray gun are more efficient, I quit spraying them back in 2011. I was spraying  "Quickliner", and their proprietary spray gun took alot of air to run. I'm admittedly rusty on how much juice the newer guns may take to run.

I bought U-POL undercoating from my local PPG paint supplier. They included the free sprayer if you bought three cans. I'll try to hunt down a bottle for the item number and find it online.  (I can't remember the exact name of their line as it was over 10 years ago I bought it.)

If I can't find it, I would still trust any undercoating from a quality manufacturer. If you have a local auto paint store, they will undoubtedly carry an equivalent.

[E5 Charger]

Thanks for the great info. I think I will be going with rubberized undercoating. I will also look more correct for our cars.

[pipeliner]

Man I hate rubberized undercoating unless you're doing a full concourse resto. If you drive it a lot it gets dirty, turns grey and looks like shit. I've sprayed several types of Bedliner and can almost copy the factory undercoating look with it. I've sprayed, line x, rhino, duplicolor, herculiner and hippoliner. For a cleaner look I like the hippoliner the best plus you can tint it to any color. For more of a factory look I liked the herculiner the best.

[Kern Dog]

Great idea, Pipeliner.

[Dreamcar]

I would personally seal any joints under the car, but it's just my opinion.

The amount of moisture getting in from the backside through factory holes and then trying to get out through the seams would be minimal compared to what would be hitting the seams head-on from the outside when driving, imo. Plus there are factory holes for drainage. Use a good seam sealer and really work it in the seam.

I coated the inside of my framerails, and plan on sealing all the outside seams. My car will not see much (or any) severe weather for the remainder of it's life anyway so the amount of moisture hitting it will be almost none-existent. None of us drive these cars in snow anymore.

Eastwood sells and internal frame coating with a tube for getting into the rails if you don't have access and aren't able to use something more heavy-duty. It may not be 100% effective, but it't better than nothing.

[72Charger72]

I researched  and asked this question here when I begin my build and decided on the Raptor Tint-able Bed liner so I can match the Color of the paint.

[pipeliner]

I researched  and asked this question here when I begin my build and decided on the Raptor Tint-able Bed liner so I can match the Color of the paint.

Had a buddy spray raptor and I still liked the Hippo better. It layed down so much better.

[E5 Charger]

I actually used the Eastwood internal frame coating. I followed a youtube tip to hit it briefly with a heat gun to straighten the plastic line and it worked really well. I taped off all the holes and it was oozing out of any seam it could find, showing it was really filling the frame rail. I gave it two coats, so it should have covered most of the inside. I sprayed the underbody with Metal Blast and then painted two coats of Rust Bullet. I ran out of nice weather, I need to have the garage door open to keep the smell out of the house, so I will scuff the Rust Bullet in the Spring and either spray undercoating or bedliner. I'm not 100% sure yet.

[PlainfieldCharger]

Man I hate rubberized undercoating unless you're doing a full concourse resto. If you drive it a lot it gets dirty, turns grey and looks like shit. I've sprayed several types of Bedliner and can almost copy the factory undercoating look with it. I've sprayed, line x, rhino, duplicolor, herculiner and hippoliner. For a cleaner look I like the hippoliner the best plus you can tint it to any color. For more of a factory look I liked the herculiner the best.

Pipeliner..are you using the aerosol herculiner or the roll on when you use it? I need to match the oem look on the interior of the rear quarters. Thanks

[E5 Charger]

I would use this undercoating for that. I haven't tried it, but I read it's the closest to the factory. You are painting over it so are eliminating the undercoating issues. 

http://www.restorick.com/proddetail.asp?prod=Undercoat

[pipeliner]

Man I hate rubberized undercoating unless you're doing a full concourse resto. If you drive it a lot it gets dirty, turns grey and looks like shit. I've sprayed several types of Bedliner and can almost copy the factory undercoating look with it. I've sprayed, line x, rhino, duplicolor, herculiner and hippoliner. For a cleaner look I like the hippoliner the best plus you can tint it to any color. For more of a factory look I liked the herculiner the best.

Pipeliner..are you using the aerosol herculiner or the roll on when you use it? I need to match the oem look on the interior of the rear quarters. Thanks

Neither one. I used an undercoating gun and adjusted air pressure to desire texture. I wouldn't use any rubberized undercoating likes rick unless it was concourse resto.