Help needed on the best way to cure under-body rust

[Ubtree]

I need to remove rust from under the sills, including rusted seams, and to re-coat them in the best way to protect them against future chips and rust. I am not too bothered about the cosmetics - after all, I don’t intend to spend many hours on my back admiring the underside of my car!

The existing paint is lacquer-coated metallic finish. There are quite a few areas which I repaired last year with standard primer and metallic paint, but this has not lasted well. Also, some seams underneath the car are starting to rust badly. What I now intend to do is:

(i) Wire-brush all rusted areas down to bare metal.

(ii) Treat the exposed areas with a product that makes the rust remaining in pitted areas inert.

(iii) Treat the rusted seams with a similar product to attack the rust within the seams and seal them.

(iv) Paint over the whole area under the sills (including the areas still covered with paint + lacquer.) with some type of chip-resistant paint or underseal.

It is years since I’ve tackled anything like this, and I am not up-to-date regarding materials. I would welcome any advice as to whether my general approach makes sense, and specifically:

1) What is the best product to render the remaining rust on the exposed areas inert?

2) What is the best product to apply to the rusted seams?

3) What product(s) should I then apply to the treated exposed surfaces and the surfaces on which there is still paint + lacquer?

4) How should I treat the surfaces covered by paint + lacquer prior to applying those products?

Many thanks.

 

[JohnD]

Wire brush to bare metal, yes, degrease with white spirit, and use "Kurust" when clean and dry. You can use a non-lacquer household paint underneath, it will give a thicker and more flexible coat. Non-drip black gloss is OK under there.

No need to strip off the manufacturer's glossy paint if it is not chipped and not rusting under the paint film. Rubbery underseals deaden noise and give stone-chip protection but do not prevent rust spreading under the layer. "Waxoyl" and similar sprays are useful inside box sections wheer moisture and rust thrive and you can't paint the insides.

If you have a reasonably modern car made of zinc-coated steel it has a fair chance of lasting as long as you keep a coat of paint intact. If it is one of the old ones made of plain steel then there is nothing you can really do, it is going to rot. Although it is possible to weld in new sills the expense of doing it to an old car is not really economic unless it is something special.

 

[114dmu]

for the loose rust a wire brush/ angle grinder with flap wheel are fine.

Treat the rust with 'jenolite' be careful it is basically an acid that disolves rust, make sure you follow the simple safety guidlines, you know wear gloves and be in a well ventilated area etc.. It works with fantastic results.

Painting is down to choice and budget, don't use domestic brands, it you want it to last then i recommend 'trimite' paints. I have used them on many applications including underneath cars, they have an excellent technical helpdesk and can recommend/suggest the best product for the job.

Do a google search for them and see how you go.

PS. I have no connection with the manufacturers of these products i am just a satisfied customer making a personal recommendation.