General Treating rust and preventing rust experience

[MultipleMultis]

I have been sorting out rusty underneath and bits in engine bay while front bumper off. Would welcome some input.

1) scrub off as much loose as possible, after pressure washing and cleaning. Then get flaking rubbery undercoat off and rust.
Grinder with cup / twisted wire brush, hand scraper - painting and decorating scraper thing, good wire brush. Getting flaky rubbber underseal off is hardest thing. Purdy decorators hand tool thing was good like a chisel.
For subframe heavy rust used borrowed air hammer with needle descaler.
Generally get all flaky stuff off and and if rusty get off as much as you can.
Pretty grim working on my back/side etc. Jack stands and wheel ramps.
2) I used Bilt Hamber 80 hydrate to treat rusty patches on subframe and body. I used it few years back on rear subframe and without any paint or anything it has done an OK job. Chemical changes rust to phosphate type but puts a nice priming film coat on as well. I put some on a rusty gate hinge back then and with nothing else it did a good job. I mostly washed then degreased using Isopropyl Alcohol. 1 tub 500 ml about £15 goes a long way
2 coats 30 minutes apart, mostly hand painted. I used spray bottle for front subframe, and some other bits near end. Then finished them with brush. Use gloves it sticks you your hands, not nasty just messy and rubbering black
3) I then hand painted at first then rattle can zinc rich primer on (Autotek) say 5 tins. Hand painting was a grim tasks - would rattle can all in future. Couple of coats
4) I then used black stone chip on top (Autotek) say 5 tins - couple of coats,
Not sure I could have not gone straight to underbody seal, but it seemed to need coating. Fairly mat soft finish. Looks like powder coating actually.
Autotek only because they make a good grey bumper paint, I have used on interior trim refinishing. Says 24 hours between primer and top coat but on hot day this seems nonsense
5) I am planning to use Black Hammerite Underbody Seal Schutz using compressor as top layer, with waxoyl product in cavities. Based on friends recommendation and he has the gun for it. Not bought this stuff yet. Not sure I could have not skipped primer and stone chip steps …

All done outside. Would have all been better in a garage, as some times too wet to paint, sometimes just too hot to get anything done. Must have put 6 or 7 days into it over many weeks here and there. I have cleaned up engine bay and refurbed the batter and air box metal work and made new intercooler bracket etc. while getting new radiator support steel cleaned up, treated and painted.
I would get those bits shot basted and powder coated in future to save time and effort and do a better job. I did same with the spare wheel carrier thing as well.

 

[widemouthfrog]

That sounds like a lot of work. Chapeau.

I've had very mixed success with shot blast followed by powder coating. For anything that can be removed, shot (or better, soda) blasting is the way to go. But unless the de-dusting is carried out to an almost OCD level, powder coat can flake off in large pieces within a few months, even if has had one of the two-coat systems applied. If edges/corners are not rounded off as much as possible prior to coating, PC tends to thin along those edges, creating a weak point in the very area that is most vulnerable to damage. Once it's breached, if the prep for the PC hasn't been perfect, it doesn't take long for moisture to creep under it and then it flakes off in large pieces.

Better to shot blast, file edges, de-dust as best you can, then use something like POR-15 Metal Prep (which I strongly suspect is a solution of phosphoric acid and some kind of zinc) to thoroughly wet the surface, allow to dry, wash off with clean water and dry that off with a hot air gun etc, then spray or brush paint with Jotamastic or Rustbuster 121 epoxy (many forums say they're the same thing) on a hot day, using about 10% thinner added. Without the POR-15 Metal Prep or equivalent, I've had exactly the same flaking problems as with PC. I've read comments to the same effect on several other fora.

If you can get Rustbuster 121 epoxy to properly key to the surface, I've found it to give protection at least as good as a powder coat. Perhaps better.

For underseal and especially cavity wax, Dinitrol is the best I've used. The cavity wax 3125 is a very runny, filthy brown liquid, but with the long wand fitted to the aerosol it is brilliant for getting into sills, subframes and seams. Brush some onto a knackered bit of rusty metal and you can watch it pull itself across the surface, wetting it out 100%. For getting into the very thin gaps between overlapped spot welded panels, it is hard to beat. It will run into/out of even the smallest gaps - even ones you didn't realise were there. That's part of the reason it's so messy to apply. Once it's dried out it gives a thin waxy film that chokes out air contact with the metal.

 

[Oletimer]

I'm a big believer in 'Old School' remedies:

Ole Blue used to get a paraffin and old oil spray underneath every July / August.
It ain't pretty and don't wear yer best suit cos it ain't a 'Sunday going to church' kinda job.
You will need the following:

Budget version: Pump up spray gun (similar to garden sprayer but it needs to be at least 5 litres) you'll be amazed how much you get thru.
A gallon of old engine oil and about half as much paraffin.

(Note: if you can do this on waste land it will save having to put plastic sheets under the car)

Method: Filter the old oil thru a piece of cloth (old tea towel etc)
Prepare the mix and agitate it well, pump up the pressure and get your pressure/spray right, you don't want to pour it on and watch it cascade off. It needs to be enough to stick but not enough to run off.

Raise the car on ramps, I always do the back first because there's always enough loose oil flying round the engine to give the front a bit of protection.

NOTE: Don't go mad round the shoes or discs, better to cover them up.
You might need to change your trousers on your first drive out if you don't.
Having done the back turn the car round and do the front. You'll be amazed how it keeps the underside in good order, the 'oil' creeps into everywhere, I never bothered too much about removing old underseal, I only removed if it was looking really tatty.

My own version of this job is almost exactly the same except: I have the luxury of a Hydrovane and an old spray gun so didn't need to do any pumping.
(If you do have access to a compressor - it really doesn't need to be a big expensive thing) Don't go nut's on the delivered air pressure, you only need about 20 to 30 psi for a spray gun and only 20 to 25 psi for a garden spray bottle. Good Luck.
George

 

[judderbar]

My suggestion is you avoid cavity wax for hidden areas that are not easy to inspect. I tried dinitrol super penetrating wax inside my sills. The results looked perfect in 2018 but if you apply this stuff to a rusty piece of metal the wax flakes off as the rusting continues under the wax. Then I found in December 2021, I got a hole and significant rusting in my waxed sills. I have learnt to my cost wax just creates another problem.

My solution is to mix engine oil and grease, (surprisingly they dont seem to mix very well), and then find a way to get the mixture into the sills and all of the hidden cavities. I have drilled some holes to make this easier so I can also scrape inside the sill where it is rusting and look from above to see the rust and get the wax off and make sure the rusting stops. This is turning into another hobby I think. I found using an inspection camera is next to useless as you never really know what you are looking at. The best way was to make up a tiny LED light on a wire and then look thru the same hole while moving the light to what you want to look at. Then you can put a welding rod or a thicker thin rebar wire in thru another hole to do the scraping and spread the oil around with a paint brush. With a bit of effort all the rubbish can be fed thru the built in holes which are usually plugged so it looks tidy inside! It is time consuming but I cannot see a way the sills are going to rust once the oil and grease penetrates the rusty areas. The wax oil was a bad idea. The sills are originally painted a light colour but with the wax they are brown which makes it harder to see inside.

My Punto was built in 2004. We need to get creative if these cars are going to still be legally on the roads.

 

[MultipleMultis]

For underseal and especially cavity wax, Dinitrol is the best I've used. The cavity wax 3125 is a very runny, filthy brown liquid, but with the long wand fitted to the aerosol it is brilliant for getting into sills, subframes and seams. Brush some onto a knackered bit of rusty metal and you can watch it pull itself across the surface, wetting it out 100%. For getting into the very thin gaps between overlapped spot welded panels, it is hard to beat. It will run into/out of even the smallest gaps - even ones you didn't realise were there. That's part of the reason it's so messy to apply. Once it's dried out it gives a thin waxy film that chokes out air contact with the metal.

That sounds like a lot of work. Chapeau.

I've had very mixed success with shot blast followed by powder coating. For anything that can be removed, shot (or better, soda) blasting is the way to go. But unless the de-dusting is carried out to an almost OCD level, powder coat can flake off in large pieces within a few months, even if has had one of the two-coat systems applied. If edges/corners are not rounded off as much as possible prior to coating, PC tends to thin along those edges, creating a weak point in the very area that is most vulnerable to damage. Once it's breached, if the prep for the PC hasn't been perfect, it doesn't take long for moisture to creep under it and then it flakes off in large pieces.

Better to shot blast, file edges, de-dust as best you can, then use something like POR-15 Metal Prep (which I strongly suspect is a solution of phosphoric acid and some kind of zinc) to thoroughly wet the surface, allow to dry, wash off with clean water and dry that off with a hot air gun etc, then spray or brush paint with Jotamastic or Rustbuster 121 epoxy (many forums say they're the same thing) on a hot day, using about 10% thinner added. Without the POR-15 Metal Prep or equivalent, I've had exactly the same flaking problems as with PC. I've read comments to the same effect on several other fora.

If you can get Rustbuster 121 epoxy to properly key to the surface, I've found it to give protection at least as good as a powder coat. Perhaps better.

For underseal and especially cavity wax, Dinitrol is the best I've used. The cavity wax 3125 is a very runny, filthy brown liquid, but with the long wand fitted to the aerosol it is brilliant for getting into sills, subframes and seams. Brush some onto a knackered bit of rusty metal and you can watch it pull itself across the surface, wetting it out 100%. For getting into the very thin gaps between overlapped spot welded panels, it is hard to beat. It will run into/out of even the smallest gaps - even ones you didn't realise were there. That's part of the reason it's so messy to apply. Once it's dried out it gives a thin waxy film that chokes out air contact with the metal.

Hi wmf, hope this finds you well.

I was ill but now OK and I am now getting to finishing off my 2004 round nose.

On the Dinitrol 3125 what wax for the cavities. ML or HS. (medium or high solids)

I will do some googling too but would appreciate any input/experience.

 

[MultipleMultis]

The difference between Dinitrol cavity waxes explained

The differences between the most popular Dinitrol rust proofing cavity waxes explained is explained in this article.

rejel.com

This says ML is correct for me. Lighter and more searching

 

[MultipleMultis]

Used dinitrol 3125 ml yesterday. It is messy but i am happy. I really seeps in.
Used air compressor.
Plastic disposable sheets under for the mess.
Bought 3 x1l cans and shultz gun and wand for 68 quid. Used 2.5 litres.
Some brushed on to save masking cills.
Should have covered exhaust in hind sight. You tuber used tin foil.
It was all clean and dry before hand. Took about 4 hours with cleaning up and learning time. Very very hot day. Paper overhalls would have been too hot. Disposed of old t-shirt I was wearing.

Need to tape up or seal somehow holes where tape taken off internal sections. Bitumen flashband I think.

Want to do doors also

 

[MultipleMultis]

Some pickies. Feel much better now she has been mostly protected.
Need to do inside doors, boot lid and bonnet cavities yet and seal the box sections under the car.