I have a California car and it still rusted in areas, undersides of the fenders, back around the gas tank and over third member big time. All surface rust but it needed to be stopped.
So, I sanded a little, wire brushed more, hit it with rust converting toxic waste, then used bed liner. I just cleaned the original deadner and painted over it. If you are restomodding, its not so critical EXCEPT if you apply thick undercoating, but bedliner can take rocks etc for a driver and looks nice. As the person who advised me, its also not nearly as ugly to deal with as undercoating...
okay, I just did my underneath (jan thru april... or was it march... don't remember, slept since then)... however, it all depends on what you want. If you haven't painted the car yet.... definitely epoxy primer and/or epoxy paint PERIOD and if you are doing a restomod vs. restoration, if had it to do over, I'd paint the bottom to match the exterior (or red oxide color.. still debating myself over that one)... Since I did mine all screwed up in terms of order, I opted to strip (wire wheel on angle grinder) everthing off the bottom and use an epoxy primer... then I tried some 3M professional undercoating just to see and I liked the look better than the glossy black... so it was a preference in looks for me... I did leave the frame rails and brackets glossy which had a good contrast...
__________________ 1966 Mustang GT RestoMod Project: 307c.i.d.,Holly 600 4brrl, TrickFlow Heads, Power Disc Brakes, Integral Power & Tilt Steering, AOD, 9" 3.50 posi rear end & a bunch of other stuff.
Project start date 1999. Completion date... fagidaboudit!
I will not spend real money on a nice car with "Goo" under it ever again, if you use it its because you are hiding something.
I'll be the first to admit I used undercoat to hide my welded seams in my wheel wells were I patched them. I really don't care.
I got a problem with people using it to hide duct tape,metal tape, screen, fiberglass screen covered with bondo, etc covering rust holes that were never cut out.... Then I got a problem with it.
There is BIG difference in how it is used and how it is represented when being sold. I would want to see before pics of what was under that fresh coat of undercoat if I were to buy one with it on.
Lynn
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'99 GT automatic
CDC Shaker scoop, K&N Filter
MAC cat back
Max Speed 1 ½” Lowering springs
KYB GR2 shocks and struts
Cobra front brakes
mine was epoxy primed then painted black satin looks good then once a year i wipe it down and it looks great i would under coat wheel wells and the tops of the fenders to prevent stones from flying and putting outy dents on your fenders just the section between the splash guards
I sprayed the underneath of my car with black Zero Rust a couple months ago and am very happy with the results. But the car is still a stripped shell so I can't comment on the longevity, but it sure seems like some tough stuff.
Jeff Speagle will usually post a picture of the detail you are searching for, on an unrestored car, that was built within a few dozen or so on the assembly line with yours.
As a buyer undercoating (tar...not the correct area sound deadener) is quick turn off.
The color IMO is important for concours show points and/or blending with original.
I have often brushed, glopped or sprayed on rubberized undercoating in wheel wells of drivers for various reasons.
I'm an odd one I freely admit. Can't recall ever in my life buying a car that I didn't intend to keep. Cars I've mantained as original were because that's what I liked not because of resale consideration!
Slim
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My '64 1/2 vert. Ordered May '64. D code 4 speed, handling package, caspian blue, accent group, Ford blue manual top.
'68 vert. driver. Owned since '77. C code AT, AC, PS, P disc B, PT lime gold, standard black interior and top. NOS RF fender and left quarter.New top and folding glass.
Thank you. I still can't beleive that's my car in bothics. It sounds silly but I have wanted one of these cars since I was 18 and thought I would never actualy own one. Turns out the only way for me to have one that was nice was to do it myself.
From the pictures it looks awesome... I love adding new stuff to my car or making old stuff look new via an angle grinder and wire wheel (or making index fingers bloody pulps, but that's another thread).
It just makes me happy in an otherwise bad situation (reference the bastard that sold this as "nearly rust-free")
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Steven
Hickory, NC
1966 Coupe
Replaced
Full floor pan
Firewall
Full cowl
Radiator support
Up next:
Shelby drop, 4 wheel drum to disc conversion, rebuild front suspension/steering, taillight panel, trunk floor,302 and AOD upgrade, wiring harnesses back in, and hopefully only patch panels on the quarters
E=MChuck Norris
Has anyone NOT put seam sealer on their trunk floor to taillight panel bracket? I kinda think it looks tacky and am wondering if there is a better alternative.
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Steven
Hickory, NC
1966 Coupe
Replaced
Full floor pan
Firewall
Full cowl
Radiator support
Up next:
Shelby drop, 4 wheel drum to disc conversion, rebuild front suspension/steering, taillight panel, trunk floor,302 and AOD upgrade, wiring harnesses back in, and hopefully only patch panels on the quarters
E=MChuck Norris
I've replaced almost all the metal on the bottom of my 66, and have spent the last month cleaning up what was left. I'm using red oxide SPI epoxy primer on it, seam sealing the seams, and will either paint or undercoat the wheelwells black. There is no way after doing all the work I've done that I'm going to put anything over it that could trap in moisture. My first thought when I look at an undercoated Mustang is "what are they trying to hide?" I'm proud of my workmanship, and if I need to spot touch-up a chip every once in awhile I'm okay with that.
I've spent hours stripping and cleaning the undercoating from the bottom of my car- I'm still not done but getting close. After all that I'm kind of glad it was there because it prevented it from rust but I won't use undercoating except for a light coat sprayed in the wheel wells. The rest is rust encapsulator, primer then satin black- it looks so good without all the goo (my car looked like fastback's goo pic). John
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"If you need a new machine and you don't buy it, you pay for it without getting it." -Henry Ford
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and if you are doing a restomod vs. restoration, if had it to do over, I'd paint the bottom to match the exterior (or red oxide color.. still debating myself over that one)... Since I did mine all screwed up in terms of order, I opted to strip (wire wheel on angle grinder) everthing off the bottom and use an epoxy primer... then I tried some 3M professional undercoating just to see and I liked the look better than the glossy black... so it was a preference in looks for me... I did leave the frame rails and brackets glossy which had a good contrast... 
