Hammerite question 2

[Jimk]

POR? Cheap? Hahaha :-D

[Scott]

I treated parts of the fence with red oxide primer before painting it with Hammerite. The treated parts seemed a bit more difficult to cover with some red bits showing through and the 'grip' was not quite as good.

Is using primer a bad idea or is it just that I should have used Hammerite primer rather than other primer?

(My assumption was that although Hammerite might be more difficult to apply to a pre-treated surface, it might last longer.)

Any advice appreciated, thanks. .

[Theo]

Last time I was painting cars, the problem with Hammerite was that it would pinhole - there would be tiny air bubbles in the Hammerite that would allow water to contact the metal, and that would then start rust bubbling through and flaking off the Hammerite.

I don't know about Hammerite's own primer, but I used Galvafroid plus spray paint on the car which did a better job. I assume if you've used a decent primer then any coating of that is main for cosmetic, UV protection and similar purposes.

Randomly selecting the Wickes Red Oxide primer:

contains Tri Zinc Bis Orthophosphate 10-25% which I assume is the protective compound, ie: assume the 'red oxide' is just a colouring for old times sake)

I don't know what the compatibility issues between primer and topcoat might be - is it possible the Hammerite is just too thin?

Theo

[Dave Liquorice]

I thoght that hammerite was supposed to be applied direct to the metal.

Yes, tiny bubbles are a problem particulary when hand brushing unless you are *extremely* careful. A second coat (within the recoat time or you have to wait weeks)(*) solves the bubble pinhole problem.

The old and mostly cleaned up and hammerite direct to the metal gate hinges I did, er, 15+ years ago are fine. Surface is a bit dull but coating is 100%, no rust bubbles.

(*) The modern stuff might not be so fussy, the orginal certainly was.

[Theo]

If I look at the MSDS for Hammerite:

It says: trizinc bis(orthophosphate) 1-2.5%

so it does have some protection, but 10x less than the Wickes Red Oxide primer.

I found it was still a problem, even if I did two coats within the recoat time. This was about 10-15 years ago though.

I wonder if it has changed its formulation in recent years?

Theo

[Scott]

Is there any need to use Hammerite primer or will any red oxide primer do just as well? I believe Hammerite uses a special solvent (thinner) but I assume the solvent is irrelevant once the paint dries.

Why a few weeks?

What about full primer followed by ordinary black gloss paint? Would this overcome the problem with the rust bubbles (and save money!)?

I take it water based paint is out of the question?

[Scott]

I mean 'full primer coating'.

[Dave Liquorice]

Toluene or xylene. I think the thinners changed form one to the other on a formulation change. The "old" thinner might have been xylene.

weeks)(*)

Hammerite "cures" rather than "dries". Under the impression that outside the recoat time you don't get a proper bond between the two coats.

ISTR that there is a similar agricultral paint that is as good if not better than Hammerite but isn't in the retail chain and probably doesn't carry the retail markup and advertising costs... Maybe <three letters>35?

[Cursitor Doom]

AFAIC, the new stuff isn't a patch on the old.

[Scott]

Would ordinary paint be just as good?

[Cursitor Doom]

There's no such thing any more (if ever there was). You need to specify exactly what you mean.

[Andrew]

I think it has, possibly to reduce the amount of ?xylene in its formulation. The change seems to have occurred when AkzoNobel bought Dulux paints in about 2008. VOC2010 didn't help either. The excellent Dulux high performance presrvative primer for softwood and basecoat sealant for hardwoods became water-based and impossible to use on previously treated wood (unless taken back to bare wood).

[Andrew]

Try asking on forums dedicated to restoring old agricultural machinery. Someone there will know if there are still suppliers of better quality external metal paint.

Who supplied the special paint for the Forth Bridge ?.

[Scott]

Leighs Paints:

[Martin Brown]

The problem if you try to recoat in the gap where the polymerisation is well advanced but not yet fully crosslinked is that the addition of a fresh solvent rich coat on top can mess up the first coat structural integrity. You have to add the second coat either inside the recoat time or wait for full cure when it is almost impervious to solvent attack.

Layers of Hammerite paint applied over the decades held my old oil tank together until the interior water line rusted through. When the guy came to lift it out of the way the base parted from the main tank at one end.

It is fine if used as directed. The metallic versions always seem to perform better at protecting metal than the basic colours. YMMV.

The old stuff was the best in its day apart from two part epoxy paints.

[Scott]

Household paint like Dulux or Crown - presumably non-water based for outdoor use.

[Dave Plowman (News)]

Dunno about now, but at one time Hammerite used a different solvent to most other paints so a bad reaction between them very common. Have you read the instructions?

[Dave Liquorice]

Just been out to thegarage my old (15+ years) tin of hammerite thinners is xylene.

weeks)(*)

Ta, end result is the same between "you don't get a proper bond" or "mess up the structural integrity". The paint falls off quicker than it should do. B-)

[Scott]

Several times. They seem a bit vague. Primer not required as this is direct to rust. However, Hammerite sell two primers (one ferrous, one non-ferrous) so clearly there may be some benefit in some circumstances. There is no warning against using non-Hammerite primer.

I am aware of the different solvent used. However, I assumed after the solvent evaporated this would be of no consequence in the same way that (AIUI) you can put oil based paint on top of water based primer.

There are also various comments that the 'direct to rust' properties of Hammerite are exaggerated.

My suspicion is that, like many products, it is just not as good as it used to be.

[Peter Parry]

Used to be Trichlorethylene (Genklene) until it got banned under the Montreal protocol.