How do I prep the surface for Fluid Film application?

[MrBClark]

So I bought about 6 cans of Fluid Film along with a 360 wand. I can always go buy more if I need. I read a lot about this stuff but I just want to know how to prep the surface. I am going to do the entire underbody of my Jeep. I plan on knocking as much rust off as I can and wire wheel/sand the surface. Then I was gonna hose it down real quick, let it dry completely, then apply it. I just want to know if I should use a rust neutralizer first or is that isnt really necessary? I only have one small can of rust neutralizer and tbh I don't want to go buy more. It is even necessary or not?

 

[GASnBRASS]

Don't bother with rust "neutralizer" sprays, I've tried various types over the years and they are all junk. The idea is that the chemicals convert iron oxide rust into some other benign stable form such as iron phosphate, but they don't have enough active chemical in them to penetrate very far. All they really do is turn the top few microns of the surface dark. Wipe or lightly scuff the area and the rust is still present underneath.

To really get rid of rust you need to manually remove as much if it as possible by sanding, grinding, scraping and then use a concentrated rust dissolver such as naval jelly (which contains phosphoric acid), or a chelation chemical such as Evaporust. Naval jelly is an acid that will attack and loosen surface rust til it can be rinsed or scrapped off, but while it's doing that it will also etch the surrounding clean metal. Apply, scrub, wait (hour or so), rinse or scrap off, repeat, with a final rinse with water to remove trace amounts and then degreased for primer/paint. And wear gloves and eye protection, it's a powerful acid.

I prefer to use a chelation product called Evaporust and have had excellent results with it. It chemically binds with iron oxide and loosens it but doesn't attack the base metal. However, the item must remain wet, and it takes a looong time to work (minimum 24-48 hours). For nuts bolts and small items, wire wheel and degrease them and dunk in a container for several days and the rust will be a bunch of black bits at the bottom. For things such as sheet metal the bulk of the rust must be manually removed, then cleaned of any grease or residues. Spray the surface with the solution and then stick a paper shop towel on the metal (surface tension will make the towel cling to the metal), and spray again to wet the towel and respray every few hours to keep it wet and the chemical will leach the remaining rust into the towel. The chemical is skin safe, leaves a slightly sticky residue, and keeps working til it gets very dark and the chemical is used up. Then rinse and degrease for primer/paint. HTH

 

[Goatman]

Try to get the insides as clean as you can. Inside frame, inside torque box, etc. Rinse and dry out. Get as much dirt sand rust grease off as you can.
This is very important.....

The stuff stinks! And not for an hour or two. For days. A week or more is possible.
I put a good HEAVY coating inside the hard doors because previous owner thought stuffing paper towels into the bottom and plugging the drain holes was a good idea. Anyway, until the fluid film pretty much firms up (it doesn't actually harden) the smell is bad. I have raised sheep for many years. And I will tell you that a wet and dirty sheep smells like heaven compared to this stuff. So allow it to air out for a while. To do it over I would still do it the same. Spraying outside areas will help keep the smell down when inside the Jeep. But I would not park in an attached garage until the odor calms down.

 

[JEEPCJTJ]

For the worst rust my TJ had, Where the skid plate mounts, I sanded and painted, then applied Fluid Film. For the other rust, mainly just surface rust at body seams, I Fluid Filmed it last fall and hoped for the best. At this point I've seen no difference in the amount of rust and plan on doing it again before this winter.