Underbody Sealant / Paint (+ my new toy)

[BZG Wagon]

Picked up my new toy in the weekend:



There's a bit of what looks like surface rust on the chassis rails. The previous owner has painted straight over it which has caused it to bubble, but chipping the paint off the rust doesn't look too bad underneath but I'd like to sort it out pretty quickly anyway.

I was thinking of sanding the rails back with a 3M sanding pad for the drill, followed by repainting it.

In terms of painting; I was thinking a rust preventative base or etch primer, followed by some under car sealant or under car paint? Does anyone have any recommendations (POR 15 comes up a lot when searching)?

I plan to use it on the beach reasonably often.

[Dell'Orto]

If you POR15 it you'll never have an issue. Provided you do it properly of course.

[Bling]

Put a pad on a grinder, drills aren't designed for that sort of thing really. Will work, but not good for drill bearings / grinder will do better faster job.

As for best way to paint it i'm not sure. I mean what are you plans for the inside of the rails? Can't imagine anything more than surface rust forming on the outside. But would be more concerned with inside if you going swimming with it.

[Adoom]

I'd use the harshest wire brush I could find with a grinder to get all the loose stuff off, then steam clean it, if possible, to get rid of any oil, etc.
If you are using POR15, there must be NO trace of oil or grease left, or the POR15 will not stick.
Read the POR15 instructions and do the proper prep.
Paint it with at least 3 coats, just keep adding coats till the paint runs out

Once that has dried properly the outside of the rails will be sweet till the end of time.

Then, use a paraffin gun on a compressor to spray a shit ton of fish oil in the rails and any other cavities, just keep going till it starts pouring out all the holes/seams, then a bit more. And you should be sweet.

[BZG Wagon]

What to do with the inside of the rails has realy perplexed me. Filling with fish oil is a great idea - is there any other sort of rust inhibitor I should look at spraying in there first also?

I thought a pad on an angle grinder would be too harsh? What sort of pad do I need to look at - something like this:


or this:

[Grrrrrrr!]

Those clean and strip discs will get rid of all the surface rust, but generally not touch the harder blue rust. If you use a wire brush cup type thing, you should really sand the area to give a it a rough surface for best adhesion. Wire brushes burnish the surface and it can cause adhesion issues with some paints.

[Bling]

Top ones get rid of paint / loose stuff. Bottom one takes off everything including metal, so slightly different jobs. Would suit different areas.

http://www.smithandarrow.co.nz/splash-page.html

Good prices, I got a clean and strip pad for my grinder and a wire brush head for like $18.

Can get the sanding ones 10 for ~$10 or something at Mitre10.

[B1NZ]

Im pretty sure there is some release by the NZTA about these rusting under the floors, Hopefully you wont uncover a bad bog job that is moments away from your car snapping in 2

[Dell'Orto]

Hopefully it will have had the floor replaced by now!

[Scottie]

www.nzta.govt.nz/resources/virm-entry-c ... letins.pdf

item 10

[BZG Wagon]

Couldn't get the link to work but if it's what I think it is then it's what's permissible around rust through the floor pan (definitely not a problem in my case - only the rails are corroded).

Had a good look at the rails the other night with a mechanic mate and as thought it looks like surface rust. The paint has blistered due to the underneath surface not being prep'd at all, and most of it came off today when I waterblasted it.

I think I'm going to go down the POR15 route - got my grinding pads all ready (thanks BZ Bling). One auto shop tried to steer me down the rust converter route, but I think sanding and painting will be the better option in the long term.

I came across this too:

A vehicle must be referred to a repair certifier if signs of fresh repair, rust prevention or under-sealing to any part
of the vehicle structure are evident.

[BZG Wagon]

Hopefully you wont uncover a bad bog job that is moments away from your car snapping in 2

Previous owner's a good family friend who's had the car for 8 years, so I know the history fairly well.

It was immaculate when he first bought it but unfortunately it's spent its life outdoors, on beaches, towing boats in and out of the sea. For a 20 year old car I reckon it's in pretty good nick. Apparently the chassis rust only appeared six months ago after he lent it to a friend who backed his boat into the sea without engaging 4wd. Got stuck, auto locking hubs won't work unless you roll forward and the tide came in and up to the running boards by the time someone came to help.

The solution; paint over the rust...

[BZG Wagon]

I did the mid section of the r/h chassis rail over the weekend. It was by far the worst.

There was some pitting of the metal which is still visable after painting it. Does anyone know whether this is likely to cause problems when I go for a warrant?

1: Grind rust and paint off rail:

(note the pitting on the bottom of the rail)

2: Clean and etch using zinc based phosphoric acid.


3: Two coats of paint (Por 15)

(pitting visable; but not as noticable as before)

Not sure what to do with the inside of the rail - doesn't look too bad from what I can see. I'm thinking of just filling the rail with fish oil and hoping for the best.

[Dell'Orto]

Fish oil or cavity wax will keep it sweet