Zinc barrier epoxy

[Burdekin]

That's nice!
Does the Jotun 80 have zinc in it? I need something with very good corrosion resistance.

No. It has very good corrosion resistance without the zinc or aluminum is the better product.

Here’s my 2cents worth with zinc and aluminum epoxy primers. Galvanising works as the zinc is a sacrificial coating, not sure you want a sacrificial substance in your car paint. Adding zinc and aluminum means you’re adding products that don’t adhere so typically they are not as surface tolerant and will be more prone to chipping. If they chip then the area is exposed and will rust. If the zinc and aluminum aren’t all connected does it actually act like galvanizing?

 

[Wildefalcon]

That's interesting. I did wonder how it worked.

I don't know, it's all magic to me.

Jotun rate the non additive epoxies as suitable for less challenging environments, compared to the zinc based stuff, so I assumed they know what they are talking about.

 

[charlysays]

No. It has very good corrosion resistance without the zinc or aluminum is the better product.

Here’s my 2cents worth with zinc and aluminum epoxy primers. Galvanising works as the zinc is a sacrificial coating, not sure you want a sacrificial substance in your car paint. Adding zinc and aluminum means you’re adding products that don’t adhere so typically they are not as surface tolerant and will be more prone to chipping. If they chip then the area is exposed and will rust. If the zinc and aluminum aren’t all connected does it actually act like galvanizing?

I think the old wisdom is get a sacrificial pigment in contact with the substrate if there's any risk of chipping or less than perfectly prepared substrate. If the coating chips, the cathode can protect even the exposed area for a long time before rust sets in and creeps under the coating.
However I agree about the benefits of Zinc Or Alu in an epoxy mastic being massively negated by the fact the epoxy resin does a good job at insulating and isolating everything, so the vast majority of the cathode won't be able to do much good.
This is where, and only where, Alkyd 1k primers are better than epoxies- in electrically protecting steel as the chunks of cathode link up during drying to form a conductive coating in contact with the substrate. This is demonstrated by the fact you can strike and arc between a bit of steel coated with bilt hamber electrox, but you can't with one coated in the epoxy mastic.
I've not used jotun with zinc or alu in it but I hear it's very thick.
I think the best of both worlds is a runny resin rich epoxy mastic which can wet out and encapsulate any remaining corrosion effectively. it will also be tough, grip really well and can have a modest amount of zinc phosphate or something in there without significantly affecting adhesion.

 

[charlysays]

That's interesting. I did wonder how it worked.

I don't know, it's all magic to me.

Jotun rate the non additive epoxies as suitable for less challenging environments, compared to the zinc based stuff, so I assumed they know what they are talking about.

Definitely always go with what the manufacturer recommends... although I have seen bilt hamber recommend using epoxy mastic over electrox for the ultimate protection so go figure!

My current approach differs slightly from the paint spec sheets in that I use a phosphoric acid solution (TM chemicals Scale X) to get rid of corrosion in pits. I keep it moving with wire brushing until I'm happy its all gone, wipe off the excess, leave dry then reabrade and degrease. It's not the "proper" way to do it (spec sheet calls for blasting) but it hasn't caused any adhesion issues on my test panels with Bilt Hamber EM.

To avoid overthinking it I think that any professional/ industry/ marine rated epoxy mastic applied as per the instructions will do an amazing job on a car.

What makes me uneasy is using epoxy mastic for repairs under a car where it might be going over keyed OE finishes, seam sealer and/ or intact OE underseal. Apparently it still stick fine if properly prepped (keyed and degreased) but there's something about the hardness of epoxy coatings which make me feel uneasy about applying them to anything other than prepped bare steel or prepped OE paint.

 

[Tim W]

sorry to jump in, I've read all the epoxy threads but still not tried any yet.
Question is, why is Jotun 80/87etc always recommended over Jotun penguard?
- I was recommended this as a good all-round first coat for automotive work, and as the other Jotun products it wlll airspray with a large tip and suitable thinning. What am I missing?

 

[Dcal]

That's interesting. I did wonder how it worked.

I don't know, it's all magic to me.

Jotun rate the non additive epoxies as suitable for less challenging environments, compared to the zinc based stuff, so I assumed they know what they are talking about.

As @Burdekin says the zinc rich primer don’t stick as well so require better prep.
The epoxy mastics are surface tolerant so are more forgiving.
If you can get perfect prep (ST3) and remove most of the salts, all of the products mentioned will perform very well.
If the prep isn’t as good, you could easily miss a bit, or you can’t remove the salts (if there is or was rust there will be salts even after blasting) I think the epoxy mastics are probably better.

@Tim W there is nothing wrong with the Penguard ranges, I’ve used Penguard Express and it dries a lot quicker than the mastics.
This is not necessarily a good thing because they have a very short pot life but they do work very well.
The epoxy mastics have a good reputation in the marine industry so are better known but there are approved and tested systems that use Penguard and will give excellent service life in highly corrosive applications (C5M for example.)
There are just so many paint systems and the range from Jotun is huge.
If you start getting into the other manufactures the choice is mindboggling and in the end it can just be down to personal choice.
If you try everything it gets hard to know what works best but I would say any of the big brands paints are more than good enough for our applications.

On spraying the 87A, below is a box I sprayed last night in a howling gale.
Cheap gravity gun and 2.5 fluid tip. The paint was warmed before mixing (left in the house overnight, but don’t tell the wife) and overthinned with 15% (by vol) thinner 17.
Overthinning isn’t a great idea but you are just making 87 into 80 so probably better starting with the 80, however the 87 can be made to spray out pretty well and you end up with more paint.

 

[Burdekin]

sorry to jump in, I've read all the epoxy threads but still not tried any yet.
Question is, why is Jotun 80/87etc always recommended over Jotun penguard?
- I was recommended this as a good all-round first coat for automotive work, and as the other Jotun products it wlll airspray with a large tip and suitable thinning. What am I missing?

There is a company who rebadge Jotamastic Smartpack for under the car and Penguard Primer for on top of the car. I'd go for Penguard HB myself if wanting a Jotun pure epoxy as it's 80% solids v 50%. I think the Jotun epoxies are very good quality, but there are plenty of other brands as well. International sell excellent epoxies along with the other car paint manufacturers. I like the Jotamastics because that is what I'm use to now and never had an issue so I have confidence in them.

I just painted my workshop with Penguard HB.

 

[Ianb]

As @Burdekin says the zinc rich primer don’t stick as well so require better prep.
The epoxy mastics are surface tolerant so are more forgiving.
If you can get perfect prep (ST3) and remove most of the salts, all of the products mentioned will perform very well.
If the prep isn’t as good, you could easily miss a bit, or you can’t remove the salts (if there is or was rust there will be salts even after blasting) I think the epoxy mastics are probably better.

@Tim W there is nothing wrong with the Penguard ranges, I’ve used Penguard Express and it dries a lot quicker than the mastics.
This is not necessarily a good thing because they have a very short pot life but they do work very well.
The epoxy mastics have a good reputation in the marine industry so are better known but there are approved and tested systems that use Penguard and will give excellent service life in highly corrosive applications (C5M for example.)
There are just so many paint systems and the range from Jotun is huge.
If you start getting into the other manufactures the choice is mindboggling and in the end it can just be down to personal choice.
If you try everything it gets hard to know what works best but I would say any of the big brands paints are more than good enough for our applications.

On spraying the 87A, below is a box I sprayed last night in a howling gale.
Cheap gravity gun and 2.5 fluid tip. The paint was warmed before mixing (left in the house overnight, but don’t tell the wife) and overthinned with 15% (by vol) thinner 17.
Overthinning isn’t a great idea but you are just making 87 into 80 so probably better starting with the 80, however the 87 can be made to spray out pretty well and you end up with more paint.

View attachment 330675

Dcal, I see you talk of salts after cleaning corroded steel, I never even knew this was a consideration, what is the best way to remove them, will thorough washing in panel wipe do it or is a proper salt neutraliser required?

 

[Dcal]

Hi @Ianb Panel wipe, or any other organic solvent, will do nothing to remove ingrained salts, it might help take it off the surface but that's about it.
You need something that will dissolve the salts and water is excellent but has the obvious downside of causing rust.
Distilled water is better and so are products like Chlor-X from Rustbuster which are specifically designed to remove salts, however all are water based and will cause rust.
There is a good discussion on salts on Rustbuster's site.
It's all good info and not just sales talk IMHO.

Page Not Found

Ooppps it seems the page you are looking is missing in action.

www.rust.co.uk

What's done in industry is mostly pressure washing, however if there are lap joints, water will fill the laps by capillary action and it is almost impossible to get all the excess water out of the joints which could create issues down the line.
Used sparingly I think products like Chlor-X have their place and I sometimes use them, but they are not a panacea.
The above is really why I bang on about epoxy mastics.
They are thicker so can withstand higher levels of salts and higher than is normally present on the underside of a vehicle.
Mastics with aluminium or mid coats with iron (MIO micaceous iron oxide) or mid coats with glass flake are even better at resisting the effects of salts (osmosis) because the metal or glass flakes (platelets) lay down in the paint layers and form an impermeable layer but there comes a point where enough is enough and when you include it's surface tolerant advantages, I personally draw that line at Epoxy Mastics with aluminium.

On another note, it's expensive to buy the kit to measure salt levels (the process is simple enough) so most DIYers don't bother and I don't think it is normally necessary.
I have only done it when I could get a lend of the kit and for fun. The levels I found after blasting were just over 100 mg/m2 which is low enough for the mastic to cope with.

 

[Seadog]

De-ionised distilled water is what's needed. Dan Gelbart did a very interesting video on preparation and finishing some years ago. It was part of his "Building prototypes" series I believe.

 

[vw1]

I have used the chlor-x from rustbusters. It does pull the salts out of the metal and it leaves a powdery surface ie the salt resadue.

Basically I ground of the rust from chassis legs and used rustbusters phos-kleen ( acid ) then once dry then apply the chlor-x