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Discussion Starter · #1 ·
I am debating which route to go when it comes to protecting the underside of my 56K mile USDM Supra Turbo 6-speed. I have considered having a bed liner coating sprayed from my firewall to my back bumper or having it primed, sealed, painted, and cleared while my motor and transmission are removed from the car. But the base coat clear the painter would prefer that my car be on a rotisserie, which I am not sure is this is still an option. I of course plan on removing all of the rear suspension, fuel tank and lines, etc. I just recently had my engine bay repainted and both front fender wells in a matte finish that matches my cars new color. Since they will be covered with the stock plastic fender well covers the color does not matter to me. If you guys have any insight or pics you could forward me, I sure would appreciate it.

Thanks again,
 

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As long as you remove EVERYTHING before coating, go for it. My parents used Raptor liner or 3M dyna pro on their classic cars and seemed to hold up forever. That being said, I assume you don't drive it in the rain/snow/salt or gravel roads so, painting would be a lot less messy for your underbody and will leave things looking more original and collectible, if that makes sense.
 

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I've heard of horror stories with undercoatings ... A tendency to trap moisture against the metal, so actually increasing corrosion/rot. If you have the option, I would say paint, as that requires a ton of prep to ensure the surfaces will take the paint. Would also look cooler, and probably be easier to clean.
 

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Undercoating is a very touchy subject with a lot of resto stuff. I would HIGHLY recommend against any bed liner coating. Bed liner poses the main issue of what happens when it fails. The coating can trap moisture behind the bed liner and hold it to the metal which will just eat away at the metal behind the coating.

I looked through many different options when Undercoating my Mk3 Supra. I had a lot of chassis repair and rust work that I will eventually writeup in a thread but in short here are the brief steps I followed:

1. Remove all factory undercoating. This stuff was a pain to get off on my chassis and you'd be surprised with what you'll find underneath. I found a few decent sized surface rust areas that would be completely hidden underneath the factory undercoating. I recommend something like this to get the job done quickly. Definitely use good PPE when doing this the undercoating frays out like silly string all over the place.
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2. Personally I repainted the underside with epoxy primer this was primarily due to the rust repairs that I did though. If I didn't have any chassis repairs to do I would have just gone a lot lighter with the wire wheel but it is tricky getting the undercoating off without removing some of the paint along with it.
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3. The undercoating I went with was 3M Body Schutz. The Square footage estimates get a little tricky I ended up using 2 Cans to do the rear of my vehicle, wheel wells and gas tank area. The official 3M Undercoating gun goes for over $200 which I wasn't trying to pay. I purchased this economy gun and it shot the undercoating perfectly!
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Depends on how much you drive the vehicle and the conditions you drive the vehicle in but also a good idea to look into fluid film to go over the undercoating. I haven't done too much research into it since my car is still not driving on the road, but the coating will help protect the undercoating even further.
 

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Discussion Starter · #5 ·
Yeah I also live in MI and have never driven my car in the snow and salt covered roads, but my garage floor remains extremely wet/damp all winter long because my wife and daughter both park their salt and slush covered vehicles in the garage all winter long. I was told that because of the paint prep work that if I chose to have it painted and cleared it would be extremely expensive. More than likely I would ask if I could do the vast majority of the prep work myself to save on labor. If I did it this way I would probably have to figure out a way to drop my car off with him immediately after prepping the entire undercarriage so that the untreated metal surface does not begin rusting while waiting on him to start my vehicle's paint job. What type of seam sealer do you guys recommend I buy and where all do I apply it. Sorry but I am as green as they come when it comes to this type of work. I sure appreciate your guys suggestions.
 

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I was told that because of the paint prep work that if I chose to have it painted and cleared it would be extremely expensive. More than likely I would ask if I could do the vast majority of the prep work myself to save on labor. If I did it this way I would probably have to figure out a way to drop my car off with him immediately after prepping the entire undercarriage so that the untreated metal surface does not begin rusting while waiting on him to start my vehicle's paint job.
Transporting the car gets a lot more difficult when the subframes aren't on it o_O

What type of seam sealer do you guys recommend I buy and where all do I apply it. Sorry but I am as green as they come when it comes to this type of work. I sure appreciate your guys suggestions.
For Seam Sealer, I used SEM 39377. This stuff is great and easy to work with, according to the data sheet you can apply it directly to metal, but personally I wouldn't. You'll need to also purchase a seam sealer gun, essentially a caulking gun specifically made to fit their product.
 

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I’m about to undercoat my mk4 and I decided to go with the 3M rubberized undercoating aerosol cans. As mentioned, undercoating is super controversial, but here’s my thought and plans. I personally think the mk4 supras have really good undercoating from the factory and the original should not be removed except for in extreme circumstances where either there is for sure rust underneath or if the car will be chemically dipped and recoated again professionally. That’s why I am cleaning up the surface of the existing undercoating by using wax and grease remover and hitting it with a pressure washer. After getting the surface cleaned, I will use a rust converter such as “krudkutter” to convert any small spots of surface rust on exposed metal. Then I am going to put down some rust encapsulator paint over any spots that I treated with rust converter. Finally I will add a layer of new undercoating without getting excessively thick with it. I did this to my integra when I built it over a decade ago and it has held up perfect, but it is also a car I never drive in snow and rarely drive in rain. I assume you won’t be driving your car in snow ever and probably not much in the rain, so I personally feel like the horror stories about undercoating won’t be likely to happen.
 

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Oh hello, what are those added rails underneath, if they stiffen a targa car, I'm very interested.
Those are the Do-Luck chassis brace. I've heard that they actually do make a difference - they're on my "gotta buy it one day" list
 

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If I absolutely had to do this job, it'd be a rotisserie job for sure. Too much metal to clean up if you don't have a good way to access it. Working on your back would suck. I guess if you had a two post lift and a lot of patience...

As for what to put on the metal once you're done? What about POR15 or Corroseal?
 
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