Hassle free rust converter to use on underbody?

[123hotchef]

Jotun Jotamastic 90 Aluminium

Jotun Jotamastic 90 Aluminium is the aluminium version of Jotamastic 90. Available in: 4.55 litre and 20 litre units. Jotun Jotamastic 90 Aluminium is a two-pack high solids, abrasion resistant, surface tolerant, polyamine cured epoxy mastic coating which can be applied in a wide range of film...

www.industrialcoatingsltd.com

I have gone for the 90 ALU I can always give it a top coat or underseal for the black look after

 

[charlysays]

If epoxy primers aren't so good why are they used on oil rigs and bridges etc? Leighs paints and Jotun both advise an epoxy primer or even just 1 coat epoxy. The top coat is only there to prevent chalking. Your points are quite sensible though so need more thought.
It is very important to use a power mixing paddle before use - the amount of solids in there is incredible. You need a good 5 mins of mixing - before you add the hardener of course. Then mix again for 1 min.

They're excellent. I'm just not convinced they give the best electrical protection to already rusted steel at the interface as a lot of the cathode gets encapsulated away from the interface. I think Alkyds still have the upper hand here.
As I said Bilt hamber have done tests and found the best result was gained with electrox primer then epoxy as a top coat. How much real world difference it makes on a car I don't know.

 

[Dcal]

Barrier 90 is very different to the epoxy mastics.
It's more like an epoxy galvafroid.
It's very good, however it's more expensive, only comes in bigger 10l packs and I think the biggest issue is it's not surface tollorant so needs to be applied over a surface blasted to sa2.5.
If you can satisfy these conditions it will pretty much last forever, but the surface tollorant epoxy mastic like 87 or 90 are probably a better bet for less than perfect prep.
Even better, use the 87a or 90a version for 'some' galvanic protection

 

[charlysays]

Jotun Jotamastic 90 Aluminium

Jotun Jotamastic 90 Aluminium is the aluminium version of Jotamastic 90. Available in: 4.55 litre and 20 litre units. Jotun Jotamastic 90 Aluminium is a two-pack high solids, abrasion resistant, surface tolerant, polyamine cured epoxy mastic coating which can be applied in a wide range of film...

www.industrialcoatingsltd.com

I have gone for the 90 ALU I can always give it a top coat or underseal for the black look after

The most I would do would be some gravitex over the top. Stay away from waxes on the underside. Inject into box sections yes, Dynax S50 is excellent. But it makes a mess on the outer surfaces of the car and is almost impossible to clean up if you want to use a dry coating. I know because I recently painted a wing which id used bilt hamber dynax UB on the arch lip and inner areas and I gave up trying to get it off (tried pure surfex HD and white spirit etc) and just did the best I could to ensure the outside of the wing and the lip wax free. Paint went on fine on the outside but yeah nightmare trying to get that bituminous wax stuff off the inner sides. once you go down that road there's no going back whereas with dry coatings you can swap and change more easily. That said, decent anti corrosion waxes like dinitrol and dynax are extremely surface tolerant and do provide very good long term protection especially if topped up every few years. If you start with an alkyd zinc primer even better. I've used the stuff on very questionable under bodywork with minimal prep (just blast off the scale and loose underseal with needle scaler) and its enabled the car to go on for a decade and die of something else.

 

[123hotchef]

I went for the Jotun 90 A because it is more surface tollerant and my chassis looks a bit flaky in please. Maybe I will like the silver finish and leave it but the vechile is black so I reakon the sliver will stand out too much and I will need to top coat black.

The gravitex is like a stone chip textured kind of paint I think is it not?

What else would be a good top coat over the 90 for a chassis

 

[steveo3002]

id just dust it over with any affordable black ...2k if you can spray it safely , the jotun will be doing the hard work protecting it so the top coat is more cosmetic imo

if you feel you need to protect the jotun then something like raptor...but bear in mind will you be scraping it off in 5/10 years ?

 

[Dcal]

Gravitex will be fine as would any top coat.
Remember to sand the epoxy if it's been on for more than a week

 

[steveo3002]

id choose gloss paint over gravitex...at least you can scrub it clean once in while and inspect for scabs

 

[123hotchef]

depends how good a job I do with brushing the jotun on!

 

[fizzy]

Barrier 90 is very different to the epoxy mastics.
It's more like an epoxy galvafroid.
It's very good, however it's more expensive, only comes in bigger 10l packs and I think the biggest issue is it's not surface tollorant so needs to be applied over a surface blasted to sa2.5.
If you can satisfy these conditions it will pretty much last forever, but the surface tollorant epoxy mastic like 87 or 90 are probably a better bet for less than perfect prep.
Even better, use the 87a or 90a version for 'some' galvanic protection

Yes I use the aluminium one.
And my trailer will be heavily blasted first.

 

[Ross365]

They're excellent. I'm just not convinced they give the best electrical protection to already rusted steel at the interface as a lot of the cathode gets encapsulated away from the interface. I think Alkyds still have the upper hand here.

I am devoted to the alkyd zinc phosphate primer that I've been using for at least 10 years. Wonderfully corrosion-resistant and I love the way the paint "takes to the metal"; some paints need to be almost worked on, but the alkyd just absorbs on to the metal so very sweetly and generates no H&S issues at all.

 

[fizzy]

I am devoted to the alkyd zinc phosphate primer that I've been using for at least 10 years. Wonderfully corrosion-resistant and I love the way the paint "takes to the metal"; some paints need to be almost worked on, but the alkyd just absorbs on to the metal so very sweetly and generates no H&S issues at all.

Which one is it and is it overcoatable with epoxy?

 

[123hotchef]

I am devoted to the alkyd zinc phosphate primer that I've been using for at least 10 years. Wonderfully corrosion-resistant and I love the way the paint "takes to the metal"; some paints need to be almost worked on, but the alkyd just absorbs on to the metal so very sweetly and generates no H&S issues at all.

and can it be painted onto metal that has not been preped so well ?

 

[Ross365]

The stuff I'm using is Johnstone's fast dry zinc phosphate primer. Johnsons make what they call "metal cladding paint" to top coat it and I always use that too. Cannot comment on things epoxy.

On my cars (underneath) I cleaned them up as best as I could (about 10 or 12 years ago) using wire brushes on drills/angle grinders, and you always accept that where access is difficult, such prep will leave some poor spots. So, on a car I think you end up with areas where you got pretty well down to the metal, then areas where you got the rust off to a greater or lesser degree and then areas where the existing paint was perfect, but you want to get paint overlap. I'm very happy with the Johnstone's primer on all three accounts. This summer, I got under one car and painted some areas which did not need doing previously, but also took a look at the areas I've done previously and was very pleased with what I found. Both cars are around 20 years old. I don't apply any black goo or rubbery stuff on top of the paint. which is great at concealing what is going on.

Are there downsides to these paints? I think you can only buy them in 5 litre cans and the recommended time between re-coats is 16 hours . I do periodically read up on other paints, but I'm staying put with what I know.

 

[steveo3002]

The stuff I'm using is Johnstone's fast dry zinc phosphate primer. Johnsons make what they call "metal cladding paint" to top coat it and I always use that too. Cannot comment on things epoxy.

On my cars (underneath) I cleaned them up as best as I could (about 10 or 12 years ago) using wire brushes on drills/angle grinders, and you always accept that where access is difficult, such prep will leave some poor spots. So, on a car I think you end up with areas where you got pretty well down to the metal, then areas where you got the rust off to a greater or lesser degree and then areas where the existing paint was perfect, but you want to get paint overlap. I'm very happy with the Johnstone's primer on all three accounts. This summer, I got under one car and painted some areas which did not need doing previously, but also took a look at the areas I've done previously and was very pleased with what I found. Both cars are around 20 years old. I don't apply any black goo or rubbery stuff on top of the paint. which is great at concealing what is going on.

Are there downsides to these paints? I think you can only buy them in 5 litre cans and the recommended time between re-coats is 16 hours . I do periodically read up on other paints, but I'm staying put with what I know.

are these cars used in winter/salt ?

 

[123hotchef]

i dont know much about paints to be honest.
I do like the jotun 87 though
so I thought it best to try the ali rich 90 this time

 

[123hotchef]

are these cars used in winter/salt ?

mine are and off road and on the farm

 

[Ross365]

are these cars used in winter/salt ?

One car (the 23 year old Rover) is the "number one winter car" simply cos it has a set of winter tyres and there ain't no buses come anywhere this village! But Oxfordshire is sufficiently far south that we don't see the sort of salt levels you get further north. For sure, Scottish cars seeing more salt seem to see worse corrosion.

 

[charlysays]

So I bit the bullet and bought 5l of Jotun 90A. It arrived thoroughly battered but not leaking (bit of a miracle) courtesy of FedEx and Rawlins offered a 5% discount on my next order. Lol.
It's a once in 25 yr job so I have the subframe and diesel tank removed.

Prep wise I'm starting with bilt hamber surfex hd. Then needle scaling everything thoroughly, then wire wheels.
This results in what looks like a nearly rust free substrate as the needle scaler seems to smash up the bits which the wire wheel might polish and the wires hook out oxides from the craters.
As a test I put some phosphoric acid on it and there was very little if any reaction so it seems like a genuinely clean bright steel surface. I would say it exceeds the minimum required st2 prep by some distance. Obviously this needs keying so I have a load of 60g mini da pads for this and some 80g larger ones for using by hand in the bits the DA can't get to. Then I'll rinse down with IPA before the Jotun goes on.

What are people's thoughts on the coating system with Jotun?
Can it be used standalone under a car?
In wheel arches I would want to use something better at absorbing impact like stone chip but under the car I guess two solid coats of Jotun, seam seal, then one more coat of Jotun of the seams/ edges then bilt hamber dynax UC should be fine? I don't mind the silver colour, it'll show up rust spots which need further attention.

I bought winter grade so with the help of patio heaters I intend of getting the coating totally applied in a day, then the next day just go over the seam sealer with more Jotun.

Re rust converters I eventually settled on TM chemicals scale-x. It's basically phosphoric acid with some other bits added. Does a decent job and on my test panels adhesion of epoxy mastic was unaffected when it was left to dry then wire wheeled and keyed up then degreased. Gives some peace of mind when you can still see some brown in a seam or in some craters which you can't get at. If applied a few times it totally removes the rust too.

 

[steveo3002]

got yourself a drill powered mixer from screwfix ...its pain to mix by hand

sounds like its cleaning up okay