Underbody painting

[Vixerfixer123]

Hi folks,just started the underside of my car,as it’s a bit rusty now,so stripped all the rubber factory coating off,and ain’t really sure what paint/protection to go for.thought about the pot-15 clear stuff,then spray a topcoat on,something like white hammerite,as the car is white.any thoughts/ideas at all?

 

[RaceDiagnostics]

I stripped, then jotun epoxy primer brushed on, then sprayed rubberised stone chip and then 2k solid brushed on. Still looks like this years later

 

[Vixerfixer123]

Thing is mate,everyone saying to avoid these rubberised coatings as it can trap the moisture,just ain’t sure what to think‍

 

[RaceDiagnostics]

Well my pics tell a different story, it's a 46 year old car that I stripped in 2018, no moisture trapped there. Pics are from a month ago.

 

[ajlelectronics]

Hi folks, just started the underside of my car as it’s a bit rusty now, so stripped all the rubber factory coating off and ain’t really sure what paint/protection to go for?

The only sensible course is an epoxy coating. If you are not going to do bodywork, then the Jotun offering would likely be more suitable as it is good for brushing. Once cured it can take anything you care to use on top, or leave it bare.

I thought about the POR-15 clear stuff then spray a topcoat on, something like white Hammerite as the car is white. Any thoughts/ideas at all?

Absolutely not. POR-15 is / was a good product but needs careful preparation and will not easily take any top coating. You can't even put an additional coat on for six weeks.

As for Hammerite, that should never go anywhere near a vehicle as it is totally unsuitable.

 

[bricol]

Thing is mate,everyone saying to avoid these rubberised coatings as it can trap the moisture,just ain’t sure what to think‍

I use underseal shultzes etc - like any coating, if it gets damaged, then bad things start to happen. But I use it to protect the paint - I don't really care what colour it is - but with mine it was originally black, it's still black and if black is what it comes in, black is what goes on. My Lancia is 34 yrs old, 207,000 miles on the clock and looking pretty good. I coated it 21 years ago, did some repairs maybe 8 yrss after daily use and parked outside in all weather. Used pretty regularly since, including through this winter. Still looks pretty good.

I'm going to carry on with underbody shultzs. But whatever you apply, follow the instructions for surface prep so it has the best chance to stick. Blasting followed by epoxy paint sticks like sticky poo to a hairy blanket - my 20 yrs of use proved it to me.

 

[Vixerfixer123]

Ok thanks folks.so if I used a rubberised coating,I would like to topcoat it in white for extra protection,so what topcoat is recommended?

 

[Turbo]

Why not get a white rubberised coating?

 

[Vixerfixer123]

Why not get a white rubberised coating?

Think that’s what I’m gonna do,but might just add a coat of clear lacquer or white topcoat still for extra protection

 

[RaceDiagnostics]

Brush on a white 2k top coat then it will be much easier to keep clean.

 

[Smallfry]

Thing is mate,everyone saying to avoid these rubberised coatings as it can trap the moisture,just ain’t sure what to think‍

In the factory rubberised coatings were applied to new metal on top of appropriate primer coats. They are good, but take a real battering over the years, and eventually give up when corrosion creeps underneath, and most of this is down to not being cleaned, impact damage etc.

What happens later, is that the same coatings are applied direct over bare and slightly rusty, possibly greasy metal, and also without the correct type of primer coat. Used to be the same with underseal years ago.

At the end of the day, its all down to preparation, and not always the fault of the product. The other thing is that once rust has got hold its impossible (almost) to stop it. nature always wins in the end.

You can get white undercoatings, I have used 2K over them, but it depends what you are trying to achieve. If its a daily driver, I would be inclined to use Jotun or Epoxy mastic and nothing else ........ after proper prep.

 

[Dcal]

Epoxy mastic as a primer coat is probably your best chance of getting a long service life for any
subsequent coating as it's designed to be applied over less than perfect prep and has at least a 20 year design life in very corrosive environments.

My go to primer for this type of work is Jotamastic 90A but there are many equally good products out there.
The better the prep the better the performance and blasting is optimal but they can be applied over hand or machine prep and still perform very well.


Last car I did was in rough shape and the underbody coating is still perfect, but that's no big deal as it's never been outside, just sat on my lift taking up room.

Post in thread '25 year old Alfa 75 back from the brink (hopefully)'

Mar 20, 2019

After letting the epoxy go off for a couple of days I then applied the seam sealer.
I used two 600ml tubes on the inside and underside.
I forgot to take a photo of the whole thing but this is what I did to every seam and lap.

While I was at this stage I remembered that I needed to install the bungs in the floor and boot.
Most of the bungs were rusty so had to make a new set.
Fortunately I had already made the dies for this (my first job on the lathe) so was a pretty simple and quick job.

Started off with some 1.2 electro galv steel.

Blanks cut to and punched...

• Dcal

• 

 

[Jelly_Sheffield]

The other thing is that once rust has got hold its impossible (almost) to stop it. nature always wins in the end.

Exactly.

Anything you do about rust that stops short of removing 100% of the corrosion back to bare metal is only ever a mitigation that buys more time before the next repair.

Any rust repair that does remove all corrosion is still only good for the lifetime of the coating... It's also guaranteed to require pretty extreme preparation steps (like dipping whole bodies/chassis).

 

[Vixerfixer123]

Well my pics tell a different story, it's a 46 year old car that I stripped in 2018, no moisture trapped there. Pics are from a month ago.

Was there any rust on this mate at all?

 

[RaceDiagnostics]

Was there any rust on this mate at all?

Yes, lots.

 

[Vixerfixer123]

Is this epoxy primer suitable folks?

 

[ajlelectronics]

Is this epoxy primer suitable folks?

For underside and suspension parts yes. For bodywork, I would be using a proper automotive epoxy primer, of which there are many on the market.

 

[Vixerfixer123]

For underside and suspension parts yes. For bodywork, I would be using a proper automotive epoxy primer, of which there are many on the market.

Yeah it’s only for underside

 

[Vixerfixer123]

Yes, lots.

Think I’m going down this route aswell