1950s Underside, frame and inmer wheel arches: clean or leave as is? '54

[Julien Abrahams]

Alright, so I was doing the brakes and noticed that the underside seems pretty dirty with dirt, old mud etc.
Tried to clean it somewhat with a brush, but it is pretty caked on there. It is completely dry, but it takes a steel wire brush to clean it.
So, simple question: is it worth/important to clean it? (With a wire brush).
In my view it is better to clean as several people told me that the mud will attract and trap moisture. True or fairytale?
I have attached a picture of the passenger side front fender.

[64\/54Cadillacking]

Yes I would clean it up. Any kind of dirt combined with water or moisture is a recipe for disaster that can cause rot. Is that picture the inner wheel well? 

I cleaned and sprayed some rubber undercoating spray on the wheel wells up front on my '54 and it looks pretty good.

My car looks to have been sprayed with that heavy asphalt undercoating that I believe only the dealership used to help quiet these cars down even more. So I have that rough texture on my wheel wells as yours looks to be smooth.

Another recommendation if you decide to clean off the mud, is to use the product called POR-15.

This stuff is amazing, I've applied a black gloss coat on the engine compartment of my '64 Cad many years ago and it still looks great and hasn't peeled off. It's much better than regular spray paint and is heat resistant.

It keeps the rust at bay and it looks good too.

I would recommend the non gloss or light gloss finish for the underside. Once it dries, it's very difficult to remove as it's permanent in many ways. You could even paint the frame rails even if it  currently has rust on it, as any rust is instantly sealed and won't spread when POR-15 is applied.

[Julien Abrahams]

Allright, so I got most of the mud and dirt off, but there are still some vague traces of it. Can I apply the Por15 (and then I assume that you mean the "Rust preventive paint") directly on to it (after degreasing with thinner (for example).
And can I use that to cover the whole underbody (chassis, wheel arches, side members,  etc)?
For me the most importatnt thing is that it is well protected. I don't care so much about the looks.

[dogbergs]

In your case I wouldn't bother with any paint(ish) treatment, no good painting non paint prepared surfaces. Just give it a good oil treatment anywhere you can get to and then take it for a ride on a dusty road. What oil? Anything really, or as Mr Vice grip, Derek Bieri would say, something with all the vitamins and dinosaurs in. Anything but brake fluid can be good advise though.

/ Johan

[64\/54Cadillacking]

Allright, so I got most of the mud and dirt off, but there are still some vague traces of it. Can I apply the Por15 (and then I assume that you mean the "Rust preventive paint") directly on to it (after degreasing with thinner (for example).
And can I use that to cover the whole underbody (chassis, wheel arches, side members,  etc)?
For me the most importatnt thing is that it is well protected. I don't care so much about the looks.

Yes, you could paint over areas that are not completely cleaned up. I would recommend using POR-15 wherever there is bare metal exposed. It might be tedious, but with patience and a paint brush, you will permanently protect the underside of the chassis.

I've heard people using "oil" type sprays that will soak into the metal and prevent rust such as fluid film or wool wax, this stuff does work great, but it's best used in areas of the body and the frame where you can't physically paint it, like all the nooks and crannies and or the inside of the frame rails.

As far as exposed chassis parts, you could simply paint the entire undercarriage, even if their is exposed rust, POR-15 seals over that rust and prevents it from worsening so it doesn't cause further damage.

POR literally means "Paint Over Rust".

I've even used this product to restore a vintage bench vise that needed some TLC.

I picked the gray color paint which sorta matched the original color, and the bench vise looked awesome as it still kept that old time original look. I've left the bench vise outside in cold damp temperatures for years and it hasn't rusted at all. Prior without painting it, the metal was very rusty.

What's great about the POR-15 is how extremely durable the paint is as it's urethane, it won't chip off and crack like typical spray paint if it gets nicked.

[Hillbillycat]

If looks don´t count I have best results with a 50/50 mix of linseed oil and white spirit.
Sprayed on with a cheap pump bottle (empty Windex bottle or such).
After a few days of curing a top layer of undercoating wax (pressure cup gun required).

Works better then Fluid Film imo.

[Julien Abrahams]

I am just a bit cautious with painting over rusted metal. I have heard stories of people using ML tectyl that they put on using a brush over cleaned metal (that was not treated with a rust remover product). Underneath the ML tectyl, the moisture from the air got trapped, and the car rusted from the inside out. That is why I am cautions, because the paint will cover it up (and you will not see anything unless it is way too late.
I also heard people using Owatrol Rustoil. Or Waxoyl.
I thought about brushing oil on it (on the completely underside). Just keeping it greasy, that could also work. Only downside: where the car is parked, it will probably drip....
It seems like there are as many opions as there are products....

[Lexi]

"Painting" over rusty metal would give rise to second thoughts with me as well. As with body work not a good idea to paint over rust. Any coating that can eventually begin to separate from the surface of the metal, is a source of concern. Should delamination occur than moisture can enter and cause further problems. Seems to me that applying a petroleum based product over the metal would work better due to its "bonding" and flow characteristics.

Like, how many parts from a salvage yard have you seen that were covered in grease or oil, that were also rusty?

I am not familiar with all of the products and techniques noted in this post but a petroleum based, non-drying product would probably provide adequate protection. Probably explains why Krown rust control and other similar companies have enjoyed success in treating cars with their rust prevention. The down side is that the process is messy and must be re-applied especially if the vehicle is a daily driver and used in all adverse weather conditions.

In the late 1970s my buddy and I chatted with a fellow one fall day as he was applying rust control to his 1959 Mercury. He had pre-drilled ports throughout the car that he used to apply a home made brew that used some airplane oils that he sprayed and also applied using long grease like needles. He worked top side as well as underneath and applied this oil once every fall since it was new. He was the original owner and it showed zero rust. And the car was white as well as his daily driver! This was in the greater Toronto area where cars routinely rusted away back in the day due to the road salt used in the winter. I was blown away and the fellow proceeded to tell us that he was getting involved in starting up a rust control business for automobiles. After our discussion it became apparent that he was using a product very similar to transmission fluid, (same color as well-red). Won't say that other processes will not work, but this sold me on what he did as I was staring at an original white colored car with zero apparent rust that was driven all year long in this "rust belt". Clay/Lexi