Zinga - poor adhesion

[Juular]

Hi,
I'm currently restoring a '88 Volvo 240. Some of the repair sections I'm making will be inaccessible after welding therefore I'm attempting to paint these with a weld-through coating.

I've just started using zinga as it's weldable, and it has been highly recommended for its longevity.

The problem is that I've just coated a number of repair panels with 2 coats of brushed on zinga and it appears to have really poor adhesion.
The surface finish is extremely chalky, and can be scratched back to a shiny finish with a fingernail.

Here are the repair panels before painting. They have been stripped back to very clean metal using an abrasive wheel, then degreased, then cleaned with panel wipe. The metal has a network of scratches which to me looks like excellent keying for paint.

Here's what it looks like after painting. You can see it has scratched back easily.

I'm going to assume this is not normal, but I'm struggling to think what I'm doing wrong. Any suggestions?

 

[grim_d]

Weld through primer is a waste of time IMO, it will burn off the area that's been welded leaving flaky areas prime for trapping moisture.

IMO you are better of blattering the area with a good cavity wax after you are finished repairing.

Not waxoyl

 

[richie00boy]

I've used zinga before. The finish is kind of chalky as its very high in zinc. Zinc doesnt adhere brilliantly so surface prep must be very good.
What kind of abrasive wheel did you use? Wire brush wheels/cups polish the surface and ruin adhesion.
What temperature did you apply the paint? Did you keep the article warm to cure? Currently its too cold for painting.
Did you stir the paint well? It takes a lot if mixing.

 

[Juular]

I used something similar to this.

https://www.screwfix.com/p/spindle-...rc=aw.ds#product_additional_details_container

The surface is quite scratched by it rather than polished I would say. You can feel the ruts with a fingernail.

Zinga claims to be ok being applied down to -15C. I estimate it was around 5C when I painted the pieces.

I'm trying another bit which I've just went over with 40 grit sandpaper to see if that helps.

The reason I chose zinga is apparently it doesn't burn back quite the same as your average weld through primer. Nevertheless I'll be spraying inside the sills etc with cavity wax wherever I can.

 

[minimutly]

Whats wrong with Waxoyl? What is the best alternative?

 

[rtcosic]

Whats wrong with Waxoyl? What is the best alternative?

Once Prudhoe Paints was sold all the Hammerite products were reformulated. All are now poor.

Dinitrol products for underbody and cavity protection would be my recommendation.

 

[Prawnabie]

In my very limited experience I have found that rotary tools do nothing for paint adhesion. You ideally need to degrease the part, go over it with 80 grit until the surface is dull and then degrease the part again. As for painting I try to warm the area I am spraying in to at least 15 degrees and warm the metal up to with a heat gun or infra read heat lamp.

 

[grim_d]

Whats wrong with Waxoyl? What is the best alternative?

What's better than waxoyl?

Dinitrol, Bilt hamber, Noxudol, thin air, a paste made of salt and vinegar...

 

[Alan Reynolds]

Hi,
I'm currently restoring a '88 Volvo 240. Some of the repair sections I'm making will be inaccessible after welding therefore I'm attempting to paint these with a weld-through coating.

I've just started using zinga as it's weldable, and it has been highly recommended for its longevity.

The problem is that I've just coated a number of repair panels with 2 coats of brushed on zinga and it appears to have really poor adhesion.
The surface finish is extremely chalky, and can be scratched back to a shiny finish with a fingernail.

Here are the repair panels before painting. They have been stripped back to very clean metal using an abrasive wheel, then degreased, then cleaned with panel wipe. The metal has a network of scratches which to me looks like excellent keying for paint.

I "aquired " 10 litres of a primer used on Pylons. I painted a test piece and I could scratch it off with a fingernail after 3 days, so no good for what I needed. Or so I thought. I tried it out of curiosity a month later. Hard as nails and I couldn't scratch it with a screwdriver. It obviously needed a long time to cure, even though it was thorougly dry. Perhaps Zinga is the same in cold weather.

Here's what it looks like after painting. You can see it has scratched back easily.

I'm going to assume this is not normal, but I'm struggling to think what I'm doing wrong. Any suggestions?

 

[Dcal]

Rotary tools are useless for paint prep, but great for removing paint and rust.
Zinga (and Galvafroid) need great prep to have any adhesions worth talking about.
If you can grit blast, it will stick well, if not a bristle blaster is excellent but expensive, next best is sand the clean steel very well with 80 or 100 grit productions paper to a matt finish.

 

[MoreWellie]

As above, blast finish gives best adhesion for zinga. It will always be easy to scratch though.

What it does do is provide really good rust protection on steel. I have bits of rusty steel that were cleaned and coated in zinga and then left outside for the last 10 years or so and still good, some of them attached to cars so even exposed to salty road surfaces.

I believe the zinc is sacrificial like galvanising.

Top tip: cut your finger nails

 

[Juular]

Right, first of all thanks for the advice.

Here's what I did earlier today.

- took a clean piece of steel

-degreased using heavy duty degreaser

- roughed the surface using 80 grit sandpaper to a dull matte finish

-degreased again. Dried thoroughly. Gave a quick wipe with panel wipe.

- pre heated the tin of zinga on a radiator. Shook thoroughly. Opened and stirred with a screwdriver for 1 minute. Seemed even thickness throughout.

- heated the workpiece with a heat gun until warm to the touch.

-painted whilst still warm

- kept the piece warm near a radiator whilst drying, 3.5 hours or so

Just went to have a look. Currently it should be touch dry. However when I carefully handled it a big chunk flaked off in my fingers. The coating looks quite fragile, almost like thin watery icing.

I'm considering going back to using cheap Screwfix galv spray as that has stuck really well on a couple of small floor patches I've done!

 

[norsa]

I don't know the actual product but have in the past used a German copper based one and latterly the upol. Whether it works or not (there are two schools) it's not designed to be top coated so you will probably be best to wash the excess off post welding and pre paint prep. Then prime your clean metal.
Nick

 

[richie00boy]

zinga is not weld through primer. its zinc primer that can be welded through.

I never had a problem with it and used one of those abrasive discs followed by scotchpad. but it was all done during nice weather and topcoated so never really got tested much.

i switched to epoxy as the zinga was a git to spray (ok fan but also stringy trails coming off spraygun) and was fussy about overcoating with solvent based so needed additional primer step.