Rust proofing under car - Focus mk2.5

[atrox]

Hi all,
 

I wanted to apply a quick and easy rust preventative/converter or inhibitor to the under side of my Focus.

I originally planned on just using underseal but i heard that can actually trap moisture and so requires a fair bit of prep to do properly.

Now I'm starting to think perhaps just some red oxide primer from Screwfix is the way to go, I was hoping to just get a wire brush to remove any loose bits and then just apply the product.

Thanks all.

[Nismex]

Always thought highly of Bilt Hamber stuff personally.

https://www.bilthamber.com/corrosion-protection-and-rust-treatments/

[Tdci-Peter]

5 hours ago, atrox said:

Now I'm starting to think perhaps just some red oxide primer from Screwfix is the way to go, I was hoping to just get a wire brush to remove any loose bits and then just apply the product.

Any hard setting treatment can trap water. Rust is unstable, and will continue to grow and change under a paint film, which tends to make the paint peel off, creating an ideal water trap.

For existing rust, the best pre-treatment is simple phosphoric acid. This is available as Jenolite, or in many other products, or just as plain phosphoric acid (typically 81% concentrate, dilute to about 24% concentration for rust treatment). It converts rust (iron oxides & hydroxides) into much more stable iron phosphate, which acts as a passivation layer, and can be painted over. For protection I just use basic Waxoyl, which does not last long on exposed parts (about a year though), but is easy to apply and does not trap water as it is flexible. Longer lasting treatments will be available, but will be much more expensive, and I have no personal experience to recommend any.

I never found bitumen based underbody seals to be of any use at all.

Be very suspicious of zinc based primers, most are useless. The zinc is contained in an insulating binder, and can not form the electrically conductive layer essential for galvanic protection. I did look at the Bilt-Hamber version, it specifically claims 90% zinc creating a conductive coating, but it is not cheap! There is no doubt that a really good galvanised style finish, with plenty of zinc, does work very well for rust prevention though, if it can be achieved.

[Eric Bloodaxe]

17 hours ago, Tdci-Peter said:

For protection I just use basic Waxoyl, which does not last long on exposed parts (about a year though), but is easy to apply and does not trap water as it is flexible. 

Going back a good while now, but I had an old (BL) Mini as a second car for years. I gave the underside, and particularly the notorious rear subframe, a thorough coat of normal Waxoyl annually and it was still in good nick when I parted with the car.

[pcaouolte]

A home made mixture of grease, bitumen under-seal and used engine oil, mixed to a firm but spreadable consistency, works well. Horribly messy to apply with an old brush but lasts for years when on. Doesn't set and doesn't wash off with normal use. Soaks into any muck on the underside of the car and keeps the water out. You really want the car on a lift or over a pit to do it properly.

[Tdci-Peter]

6 hours ago, Eric Bloodaxe said:

I had an old (BL) Mini as a second car for years. I gave the underside, and particularly the notorious rear subframe, a thorough coat of normal Waxoyl annually and it was still in good nick when I parted with the car.

If a treatment can keep a 1970s / 1980s BL car even partially rust free, then it has to be effective. Those cars usually had rust holes in them by about 3 or 4 years old! I well remember constantly patching up the bottoms of doors, sills and wheel arches that had rotted right through.

Corrosion resistance of cars improved massively sometime in the 1990s, my second (J reg) Sierra had hardly any rust. The Focus I have now is slightly disappointing there, maybe not as good as that Sierra, and, sadly, not as good as the Vauxhall Vectra I had after the Sierra. But the Focus is better than the Vauxhall in every other respect!

[stef123]

I have used Fluid Film on my van, with the proper spray gun/lance setup its easy to get into all the cavities and box sections. It needs topping up annually but does not dry out or wash off. It can be bought in large bottles or small aerosol tins which are handy for touch ups/disturbances. Fluid film also neutralises existing rust so fingers crossed the areas you cannot see but can spray a mist of the product in will be fine for years to come. 

Fluid Film looks to be comparable to Crown rust proofing. If you have access to do it yourself will save you hundreds of pounds however. When my van needs doing again, perhaps if someone reminds me I'll do a write up lol. 

[Ennvoqation]

I'm looking into getting the Dinitrol service done on my Focus just before autumn, the process takes around 5 days to complete as they do the sills, wheel arches, underside, cavities and so on. The process isn't cheap but considering the cost of getting a car repaired for rust (and most of my previous Focus have rusted wheel arches/sills by the 5 -6 year point) I consider it worth a punt. They also do yearly checks and I'll be getting the clear coat applied so it'll make inspection easier.

I also believe MoD vehicles get the same coatings to protect them.

[williamweb]

2 hours ago, Ennvoqation said:

I'm looking into getting the Dinitrol service done on my Focus just before autumn, the process takes around 5 days to complete as they do the sills, wheel arches, underside, cavities and so on. The process isn't cheap but considering the cost of getting a car repaired for rust (and most of my previous Focus have rusted wheel arches/sills by the 5 -6 year point) I consider it worth a punt. They also do yearly checks and I'll be getting the clear coat applied so it'll make inspection easier.

I also believe MoD vehicles get the same coatings to protect them.

After spending  about £1000 on rust issues over the last 2 years on my beloved mk1 I think prevention is the way to go and I will be looking into it when I make my next purchase 👍

[Eric Bloodaxe]

11 hours ago, Tdci-Peter said:

 I well remember constantly patching up the bottoms of doors

Unfortunately I didn't do the doors.............! 😀

[sonic113]

I did my car about 4 years ago by hand with the Hammerrite Underseal with added waxoyl. I just give it all over a good power hose underneath and let it dry out over night then painted it all on with a brush. Its good stuff and sort of keeps active where other underseals will harden , this one will always not fully dry. For the metal parts for the subframe and other metal parts I painted them using black hammerite satin.

This has held up very well for the last 4 years to be fair as the roads and salt out our way through the winter months are really bad. At the time it was a cheap practical option for me. Im thinking about redoing it all over the same way this summer but might see what others here are doing and see if there is a better option. I will keep an eye on these thread. 

Cheers

 

 

[atrox]

Thanks all, lots of useful info.

I'm leaning towards Jenolite now to convert the rust after removing any flaky/loose parts then just using waxoyl to protect afterwards.

[Tdci-Peter]

5 hours ago, atrox said:

I'm leaning towards Jenolite now to convert the rust after removing any flaky/loose parts then just using waxoyl to protect afterwards.

Jenolite, and most rust convertors / stabilisers are acidic. They sting when splashed on skin, I can vouch for that! Takes a while on tough skin like hands, worse on more sensitive parts! Just wash off with water asap. But you will not want it in your eyes, and I have had eyes full of rust and muck after working under cars, so I wear safety glasses now, though they are never 100% effective.

It does not seem to harm paintwork, I have used it often on scratches and chips on paint, and it does get under loose paint to stop the rust there quite well. I wipe any excess off rubber gaiters, hoses and cables, but again I have not seen any harm done by a bit of accidental coverage. Apply generously to bad rust, and leave up to 24 hours for it to work. All the nasty brown rust turns black, and smoother.