https://www.google.com/search?client...d+undercoating

I was wondering it's because of lack of prep, which cause the coating to trap air/dust and that's when moisture gets in.
However, why in those videos, people don't talk about prep or good primer/rust converter? Is something else into this?

What are the not so expensive alternative?

 

Today Woolwax, Fluid film, and a variety of cosmoline type products are highly regarded. The preferred undercoatings used in the 60's and 70's were oil or tar based and are no longer available. I believe a tough rubberized coating combined with proper prep can provide great long term protection...hence the Rhino liner in the bed of my truck. Rhino Liner and Line X both work well to protect a variety of vehicle surfaces. Where the trouble occurs is on the underside and limited access areas. These products work well when applied to uniform surfaces well prepped without any remaining corrosion. If applies over corrosion, or in any manner that results in trapped dirt & moisture then the trouble starts. As a single example say the bed underside was coated when the vehicle was new. Now what you see is "protected" unfortunately, dirt and moisture will find their way inside the bed stiffeners and rot them from the inside out. Good Luck, Russ

 

Where are you located in the USA? What condition are the parts you want to coat? It will make a difference on the longevity of the coated parts. B.

 

Look up Krown.

 

I live in the Virginia. There are surface rust. Looks like the I will go with the clean up and rust reformer route then something on top.

Interestingly, one day I was helping replacing an oxygen sensor of a honda civic, I think the year was 2001. The car was rust free at the bottom for someone who never do a car wash and not maintaining it. My thinking was that the car was driven very early in the morning every day. That's when water condensed on the car when cold air starts to get warmer. Driving like that somehow preventing the water moisture of forming and causing rust. Also, if there is salt splashed on it, the regular driving would help clean it up via rain. Vehicles that are left sittings are the one that got the most rust.

 

I just watched Krown since you mentioned it, from ErikTheCarGuy channel. It appears to be a good method, especially it goes into the rust, and they claim it even peels off the rust over time.
I am wondering how hard to work down there with that, and how much it costs, since it needs to be done probably once every few years at least. Probably every good idea for inside the frame, where rust can't be removed and hard to reach.

 

I paid $145.00

 

Check out Woolwax. Used by most DOT's on their equipment.
https://www.woolwaxusa.com/FAQs_ep_45-1.html

 

TL;DR Yes, it's that bad.

If I had the time and money (either to do it myself or to pay someone to do it for me), I'd take the cab and bed off, strip the frame of all the rust and coat everything with something like Chassis Saver or Eastwood's Rust Encapsulator. My first DIY attempt to address the rust on my truck was with a certain well-known rust paint and the results were plain terrible. After around a year later, the paint was peeling off and the rust seemed to have gotten worse. Unless you use some kind of a chemical to neutralize the rust, you're only covering it up just the same as hanging a picture in front of a hole in the wall; this especially goes for rubberized undercoating which seems to harbor moisture and really exacerbates and accelerates rust while still looking OK on the surface. Every truck I've seen with it (that isn't a recent application) has it peeling off revealing really nasty looking rust underneath (think heaps of salt on raw steel).

Since my pretty dreadful experience with painting I began using Fluid Film although there are certainly others such as Woolwax, NH Oil, and Krown. I believe Project Farm even did a video testing many of the popular undercoatings and Fluid Film was one of the best.

Things do get a bit messy when you have to work underneath the truck but it's nothing a rag and a pair of gloves can't fix.

I try to undercoat twice a year: sometime in the spring or summer and then another application before the winter. The spring/summer application has the benefit of setting up before the winter weather; a fine dust of dirt from driving gets thrown up on the fluid film causing it to become much more durable. It's not going to be a messy eyesore either. In fact, I had someone question whether I had painted my frame! Obviously at first your frame and everything you coat with it will look oily and greasy, but over time the dust and dirt will stick to the undercoating leaving a matte black appearance. Many of the oil undercoating companies are beginning to offer black tinted variations of their product to aid in aesthetics which I'll likely switch to once I exhaust my current supply.

Something else to consider is that the oil undercoats will creep where paint can't, such as the rocker panels and bed floor rail supports which are two problem areas on the Super Dutys.