So I've got all the old undecoating off my car and the patch panels are done. Everything is bare sandblasted metal. I'm hesitant to put on new undercoating cause it looks to me that it causes more problems than it solves. If water gets behind the undercoating, it holds the moisture to the tin and CAUSES rust. This is a car I plan on keeping a long time. Should I just paint the underside , undercoat it, or do sumpin else? Are por 15 or Rust Bullet good in a situation like this? Do they REALLY work? Whats gonna protect this car best from rusting out all over again?
I've stripped off enough undercoating to never put it back on anything... The metal always seems to be a rusty mess underneath. I've used Zero Rust with good success, it's a similar product but I've seen a few tests between it and POR and it came out way on top. I've got a satin gallon in my office waiting for something (can't really find a use for it on my AV8, it was for the undercarrage of a Cougar I had but sold), but none of the rust encapsulator stuff can stand up to UV rays, it either has to be topcoated or in shot on panels that aren't regularly exposed to sunlight (like the undercarrage).
what about a paint on bedliner, or insulation... provides some of the same effects, and come is cool colors... and easy to keep clean... just an option
I used por 15 on the bare metal and then covered it with gloss black to hopefully seal it. Inner quarters with por and then 3-M Body shutes. So far so good
The old undercoating was basically thinned down tar and was usually sprayed right over the bare steel. Hence the rust problem that many old cars have . Since you have everything to bare metal the best next step is to prime all bare metal with a self etching zinc based catalized primer. Once this is applied follow with a good quality chip guard material , top coat with a semi gloss black or color of your choice. Used this process on several cars, some over 25+ years ago, with no sort of troubles. The zinc primer is the secret. Just stay with a good brand name manufacturors product. The 3M chip guard is a good choice and comes in a tan or black and is widely used in the repair industry. IMO this is the only way to go.
If the entire bottom of your body has been sandblasted, a good epoxy primer is the best choice for adhesion and rust protection. once the epoxy is sprayed on, then you may put whatever you want over top of it. depending what kind of finish (texture/color) you want.
zinc based etching primer is not a bad choice for as far as rust protection goes, however when you are using any of the zinc based etchers, the top coat that you put on is more detrimental than when using an epoxy. an epoxy can stand alone as long as uv ray exposure is not an issue. zinc based etch primers do not have the durability to stand alone, hence the topcoat must act a debris protection for the zinc etch. Also, if you choose to use an etch, make sure you use an acid based two part etch, rattle can mek etch is NOT the same.
what I do is epoxy prime if its nice white blasted steel, por 15 if its less than virgin. Then over that I use an undercoat made by Wurth. Make sure to scuff the por15 before you undercoat it. It is by far the best looking undercoat I have ever seen. You dont get the nasty sharp peaks and deep valleys you get with some, but a nice, even pebble finish. My description does it no justice, fwiw, thats what I did on a car I worked on that sold at the Gooding and Co. auction in Monterey. no undercoat shots, but here is the car http://www.goodingco.com/auctions/catalogues/pebble06/lot46b.html
Most undercoatings can be painted (or at least the stuff I use can be). I put a gallon on the bottom side of the 50 after I got it clean. Thinned it with lacquer thinner and it sprayed out like paint.
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