underbody/frame coating recommendations

[rreegg]

Hey all,
I'm going to be installing a new tow receiver on the '88 soon. the frame seems to be in good shape with just some surface rust. been thinking about doing some underbody coat while i'm down there - probably after drilling the holes
I don't have a pressure washer but have osc. multitool and angle grinder - how much should the frame get cleaned up before spraying? To be honest if I wasn't down there bolting the receiver I wouldn't be worried about cleaning things up.
Additionally, any advice for a good underbody coat? I've got some left over: bed liner spray, rust resolving spray, rustoleum spray paint, and some self etching primer. Obviously they also make rubberized undercoating spray but unless someone swears by it I'll just go with other stuff laying around
It's pretty wet and cold this time of year where I'm at too - spray paint usually cracks/ripples when it's cold so that's just another consideration

cheers

 

[Brian VT]

Around here, in the Rust Belt, most use Fluid Film or NH Oil Undercoating.
They are messy when you go to work on something later but they do work well.
I would stay away from solid coatings such as bed liner spray. Water will eventually get under it and then it's trapped in there.

 

[franklin2]

I like and have used rustoleum rusty metal primer. All you have to do is get the loose rust off, and the rusty metal primer will stick. It does work better if you brush it on, but that can be time consuming and difficult to get in certain spots. I usually do a combination of brush from a quart can and a spray can. You can leave it red primer or topcoat it with a rustoleum color.

 

[chillman88]

Obviously they also make rubberized undercoating spray but unless someone swears by it I'll just go with other stuff laying around

I swear AT it. I've seen several vehicles up here in the rust belt where the rubberized coating dried up and held all the salt and moisture directly against the metal actually rotting them out faster.

If you're inclined to paint it, I'd use a good primer and a gloss paint. That should provide a nice smooth surface that's easy to wash.

Whatever you do though, something like fluid film or woolwax, or any oil type undercoating is the best option. They don't hold up forever and will need annual application, but they provide the best protection from what I've seen.

 

[46Gunz]

I have been using this black cosmoline under different situations to see how it performs. Like on rusty frame, rust knocked off with wire wheel and fully cleaned up rust (almost all) removed. The rust knocked off with a wire and wiped with brake cleaner seem to work best and last longer, for not a lot of work.

RP-342 "BLACK" Military-Grade Rust Preventive Spray

Now Available in BLACK - Our Strongest, Longest-Lasting (and Fastest-Drying) Rust Preventive Aerosol, PERIOD! Offers the highest concentration of Industrial-Grade Cosmoline® available in a convenient Aerosol Can. 1-coat protects all metals, iron, steel (stored Indoors or Outdoors) for Years...

www.cosmolinedirect.com

I recently had the bed off and replaced the rear fuel tank. While doing this I replaced the rear spring brackets and cleaned up the rusty frame and cross members. I used this KBS product and I think it work pretty good. More time intensive but good results.

RustSeal - Rust Prevention - Stop Rust Paint - Frame Paint and Concrete Sealer

www.kbs-coatings.com

 

[Bart F-350]

I have been using this black cosmoline under different situations to see how it performs. Like on rusty frame, rust knocked off with wire wheel and fully cleaned up rust (almost all) removed. The rust knocked off with a wire and wiped with brake cleaner seem to work best and last longer, for not a lot of work.

If you treat the frame with a wire wheel, you're smearing all the rust and grime etc. in a layer covering the rust, it looks clean, but isn't (try to scratch that (new) layer with a sharp screwdriver or so)
If you then cover that layer with the product of your choice, it will act as the before mentioned rubberised layers and trap moisture and rot out the frame quicker.
You better use another cleaning methode.

Another good tip, wait until weather is dry and around 10*C or higher to apply products, if moist and cold the products mostly will not stick well to the frame.
A paint cabin might be an alternative?

 

[hacked89]

I use farm implement and rustoleum for any spots the brush doesn’t hit

 

[david85]

Fluid Film Fan here.

Although it's a good idea to inspect and apply fluidfilm (or equivalent) annually, the protection doesn't drop off a cliff if you don't. The hidden areas are still protected because the stuff is sticky, doesn't dry out and migrates across surfaces. The consistency is similar to a low viscosity grease. I spray it inside all the drain holes of the body and it's still leaching out over a year later. Same for wheel arches and cab corners. The stuff is absolutely tenacious and will get everywhere with enough time. No product that fully cures can come close to that. The only real drawback is it makes the body look messy where it leaches out and migrates across the paint surface. I'd rather have that instead of a rust hole, but some folks are bothered by it.

Cosmoline is a nice product, but I've seen how our industrial spare parts can still rust in the crate. Never tried it on a vehicle though.

The last time I used undercoating, it was on surfaces that were already clean with good paint or rust converter already applied. I would NEVER apply any kind of asphalt or rubberized undercoating on surface rust for reasons already mentioned. It does more harm than good.

 

[chillman88]

Food for thought for whatever it's worth. Something like fluid film can be washed off if you have to work on something. Cosmoline dries and would take a lot more to get off if it's in the way. I'm thinking about wiring repairs and stuff that are inevitable on our old rigs.

 

[david85]

Food for thought for whatever it's worth. Something like fluid film can be washed off if you have to work on something. Cosmoline dries and would take a lot more to get off if it's in the way. I'm thinking about wiring repairs and stuff that are inevitable on our old rigs.

I hadn't thought of it that way, but you're right. Fluid film will generally stay attached unless directly next to the tires and at highway speed in the rain. Which means that with a mild pressure washer, you can remove it. Cleaning off undercoating is very time consuming.

 

[CDX825]

Fluid film/ Woolwax or Blaster surface shield.

Fluid film is great for inside of body panels because it creeps into the pinch seams and stops them from rusting out. Use it inside your doors, fenders, tailgate etc.

Last year was my first year using woolwax. Its lanolin based like fluid film but stays put better. I used it under my work van and a year later it still looks good. Fluid film tends to wash off in areas under the vehicles that get the road spray from the wheels. Woolwax holds up a lot better in this regard. I actually had to heat it up to spray it from my fluid film gun.

Blaster surface shield is another new product to the market. This stuff holds up great in and around the wheel wells. Its also good for anyplace the will get heavy road spray. They sell it in bulk but I have only used the spray cans of it so far.

 

[77 F-250]

I tried chassis saver on my last frame for a base coat. Sticks to rust like glue and flakes off clean metal. Rustoleum is good as well. If correctly applied fluid film has great results.

 

[captain720]

I’m thinking about trying something, the car dissolver is already getting to mine as I do about 200 miles a week on a heavily de iced road.

 

[Weldingman]

+1 for fluid film/woolwax.

 

[Bart F-350]

one year ago I sandblasted a frame and put a paint system on there like a new one.
one drawback; you can't do that in a week-end :-(