rugerben

Ok, so I want to strip down one of my frames and get it painted.

I can get it powder coated, or I can get it sprayed up at an autobody shop.

Which is going to be more durable? This is for an every day/bad weather commuter bike, so it's gotta be a pretty tough finish. Esthetics come far secondary to durability.

So what say you?
Which is more durable? Auto paint, or powdercoat?

Scooper

Powder coating will be more durable than paint. Powder coating is especially suitable for every day/bad weather commuting bikes.

unterhausen

a well done wet paint job with a clear coat is pretty durable. Most people that specialize in that kind of paint assert that it is just as durable as powdercoating. However, for no good reason, I suspect a local autobody shop would not do this particularly well

Allan Pollock

for both powder and paint, the quality of prep work is everything. No matter what, the shop that does a better job stripping and cleaning the frame will give you the best finish. Find a good shop that you trust and woks on bikes regularly and give them you business.

Allan

NoReg

Powder coat is a tougher material, but it can lift right off parts unless properly applied, and it has a reputation for porosity and not excluding the weather all that well. Rust can actually grow under it.

I agree about quality being the key, but you probably don't want to budget what quality costs. If you can find a nice local powder guy, they will often do a far better job for the bucks than a painter will do. This assumes you are not getting a person with experience in bikes. I think in that case powder has an advantage.

But possibly what you should be considering is which finish is the most repairable. There aren't bulletproof, cheap, finishes for carbon steel bikes. If you want to lean it up against nasty surfaces copy your local bike courier, cheap paint that can be repaired, and lots of tape. I touch up powdercoat with crazy glue, so far it seems to work.

KNEEL

On one of the first frames that I made I had it powdercoated clear, I liked the look at first mostly because the four hundred and some degrees that they pre heat and then bake it at turns the raw metal the color of straw. The bike was a cross bike so it took some abuse , the interesting thing was that every where there was even the smallest nick in the coat , rust would develop underneath the coating and since it was clear, you could see it, I did'nt ride the bike very long but I kept it around to keep an eye on it and after a year or so there was more spider veins and out right rust than I was comfortable with, the coater that I use does mostly medical equipment so I dont know if they did something wrong or not but I imagine that the same thing would be going on with colored coating. My guess with paint is that a coat of metal etch and then a good primer under the paint goes a long way towards keeping the bike healthy.

I have had both methods done on bikes since that bike and every time I see a new nick in powdercoating I think back to the clear bike.

25hz

I would second what Allan and Peter have said. Being a painter too, proper prep for either paint or powder is about 90% of the work, shooting the coating is a fraction of the time. Like paint, there are a lot of different kinds of powder and some work better for inside applications, and some better for outdoors. I've seen rust grow under powder too, but in those cases, it's generally been because the powder was put on in too thin of a coat. Economics obviously come into play, but when the powder is put ojn thin, especially in only one coat, apparently microscopic holes between the grains allow easy ingress of moisture straight to the base metal. For chips and scratches right to the metal, any coating will allow rust to start forming. I do like the powder coats for their improved toughness, but the coating has to be applied properly.

rugerben

Wow. Thank you for all your advice guys. Now I'm not really sure what to do. I think I'll cover up the nicks in the original paint and keep the original for as long as possible.

meanwhile

Neither. Use a two part resin paint. Car restorers use them to chip proof underbodies - they're that tough. The most rust proof is probably Epoxy Mastic, a Norwegian product developed for the oil industry. You don't get much of a colour choice, but it is tough! (It's what I've decided to use on my bike come the autumn.)

See https://www.rust.co.uk/epoxy-mastic.cfm

Oh - and you can put it on with a brush and won't get marks.

meanwhile

I've lost the URL for this - it's from the CTC website - but it's superb. It's for really rusty frames but still useful in general, if a little OTT:

by MikewsMITH2 » Sat Jul 25, 2009 9:25 am

I'm afraid paint won't stop rust coming through, to prevent this the rust needs to be neutralised first. This is what you need to do:

1. Strip back to bare metal using Nitromors paint stripper.
2. Sand down until all surface rust is removed.
3. There will still be rust in the pits - sometimes so small you can't see it. To neutralise this you need to use phosphoric acid. This is available in gel form from Halfords and the like as "Hammerite rust remover". This is a very weak form and will work but you may need several 2-3 hour application cycles before all the rust turns to a blueish colour. The best stuff to use is "Jenolite" from jenolite.com or "Milkscale remover" from an agricultural merchant. This is stronger and cheap.
When the rust is neutralised use "Hammerite Number 1 rust beater". This is a zinc phosphate rust proof primer.
4. Then prime and paint as normal.

This process has been used in classic car restoration trade for many years and done properly this will definitely kill the rust. I have done two rusty 1960's frames (one very rusty) and used one all last winter with no recurrence of the rust. If there is much rust on the frame it's probably best to get it media blasted, but still use the jenolite/milkscale remover as the blasting process will not remove all the rust in any pitting there may be.

Another tip is to use plenty of paint to make sure moisture cannot get through. A 2 pot epoxy paint is best as this is totally waterproof whereas convential enamles aren't. I also clearcoat the the whole frame after the transfers have been fitted. Plasticote is the correct stuff for this as it won't damage the transfers. I also wax mine with car wax after the paint has hardened. The only problem with professional re-enamelling is to make sure they are using the correct process of blasting/dipping to remove and neutralise any rust. Obviously if your frame isn't rusty then stripping, priming and painting is sufficient.

NoReg

Just by the by, I don't know of any epoxies that are completely waterproof. They will all (?) eventually pass water through in tests that are designed to see how long an equilibrium of moisture takes to establish itself. Of course that may not mater in this application, since steel is not a block of wood in a vapour environment.

I have been told the same positive things about 2 part epoxies, as mentioned above, from various sources, my only concern is whether they are UV strong. Some frames will be stored indoors and see few days of sunlight per year. A bike that sees a lot of light needs to be UV resistant. Epoxies in my experience chalk up and need a top coat of LPU or some such. This is why the epoxy primer and LPU topcoats formula is popular.

Now if anyone know a product that will prime metal for high gloss latex house paint...

Falanx

You won't find a waterproof epoxy paint at all, and for two good reasons;

1.) There's no such thing as a waterproof plastic. End of.

2.) Epoxy system paints were originally developed to be the primer body for high-durability, extreme service applications, such as aerospace and marine, and by peopel who understood and accepted that all polymers no matter their thickness or chemistry allow water and gas transfer. Almost all aeospace calibre paints are epoxy primer based and that primer is not only porous, but the porosity is intentional. Strontium chromate and zinc-potassium chromate bearing films are laid down on top of aluminium, steels, magnesium and titanium alloys to cathodically protect the substrate but they cannot do that without being electically connected to both the substrate and the interface with the next paint layer.

The intention here is to put a hopefully, mostly waterproof, ish, barrier coat down on the top of this epoxy and once, eventually water has managed to get through it, then the primer/protection can do its job.

This said, epoxy undercoat primers are remarkably durable when properly topcoated. I can recommend Indestructible Paints for any of their systems. They sell mostly to industry, but you can deal with them in small quantities as a private purchasor if you don't mind paying for the best.

meanwhile

That's very interesting and very useful - thanks! I shall ask questions of manufacturers etc.

Por 15 Hardnose is claimed to be extremely UV strong... Now I've checked to Epxoy Mastic that detail seems to have been skipped. Suspicious!

meanwhile

Really??? I didn't know that - that's fascinating.

Porosity is a side effect of this? Or is porosity itself the electrical connector, via the flow of ions through it?


So that would be a zinc(?) primer, epoxy, top coat sandwich???

That's interesting too.

Ok - if someone was painting at home and wanted maximum toughness and ease of use, are there any reasonable options? What about Hammerite? Or Por 15 Hardnose over something like zinc oxide primer? Assuming the Hardnose is UV resistant would the combination be a good one?

unterhausen

I have some bikes I painted in 1980-ish that have been badly abused and have some chips off of the paint. The primer is still holding up. It's amazing.

Falanx

Essentially, it's a fundamental of polymer chemistry. Even the most rigid, cross-linked, three-dimensional polymer structure effectively terminates in lots of places rather quickly, so what's left holding these ten-thousand molecular weight monsters together is dipole interactions and Van der Waals forces. Essentially, static. Gas molecules, and tiny liquid molecules can elbow their way through with enough head of pressure. That's why beverage bottles have a shelf life.

More... the porosity is capitalised on. The pores allow ion transport and therefore maintain the continuity. The paints are designed to go down in a film thickness range x-y and in that range there can be assumed a surface-connecting porosity range usefull but not excessive.

That would be.. (etch primer if it needs it), strontium/potassium-zinc epoxy primer, topcoat. Yep.

You want maximum toughness, I'd say polyurethane topcoat and a good sacrificial epoxy primer. I had to get a Mil Spec PU paint off once. It took a oxy-propane torch and glass bead blasting. No joke. Two HOURS. But it's once again, all down to the prep. You make sure the subsrate is clean and keyed, you take your time with the primer and then you key it again, unless you're handy with putting down a final powder layer on the primer. Be aware that the two are partially mutually exclusive. A wet-coat car paint is real easy to use, but not particularly hardwearing by comparison. A PU paint is a bit of a pig to clean up and strip out of spray tools, but it won't come off, and the chemically resistant nature as a paint is reflected in its behaviour as a film coating.

meanwhile

Except the last sentence about about beverage bottles, it's easy to imagine Tom Baker giving the above as an explanation of why the Tardis isn't working! But yes, that makes perfect sense.

If you get a moment I'd be interested to know what you think of the info for the site for KBS Rust Stop. They claim that:

And it's a "Polymeric Isocyanate" according to

https://www.kbs-coatings.com/RustSeal...a_ep_45-1.html

I noticed that one of the magazine articles archived on their site claimed that an angle grinder was required to remove this stuff, and even that had problems. It's designed to be used as the middle layer layer of a 3 layer sandwich, btw.

Thanks!

Falanx

Uh-huh. That means polyurethane. And it's BS. 9 dollars for the protection that RustBullet over here charge 43 quid for? The salesmen are talking. The tech department probably threw a sh*tfit when they saw that.

I'm sure in most cases that their PU coating does block the majority of moisture. But oxygen and water vapour it won't stop, or they'd have tested it in water vapour and listed the results on the page. For reference, just because things like sulphuric acid are listed on there, it doesn't mean very much. All of those materials the coating has been tested in shouldn't affect a protective coating that claims to meet ASTM-B117. All aerospace quality and marine quality coatings must pass ASTM B-117 with flying colours. It's just a normal 5% salt fog test. Hell, we test everything in that, even aluminium.

As for the blocking pores - that's technically true, if you accept 'pores' can mean anything. I think that's the angle they're working.


That sounds like PU. It just clogs the damned tool.

meanwhile

I wondered. I checked on wikipedia, but it didn't say anything useful.

It it isn't impolite, can I ask who "we" are?

Yes - I wondered what you'd say about that and whether "pores" in steel had some sort of technical meaning I was unaware of or was sheer bs.

This might interest you:

One thing still puzzles me - why a PU coat on top of the epoxy? My belief is that the zinc is for rust inhibition, the epoxy for toughness, and the PU for UV resistance - but aren't there some epoxies UV resistant now, eg Por 15 Hardnose? Would a layer of this directly over zinc primer work well, do you think?

Falanx

I'm aorry, but I can't tell you, I don't think. The company I work for has military and commercially sensitive clients. It's one of the bigger third-party aerospace companies, though, if you want to do the guesswork ;-)

Nope, nope. Not like that.

The zinc's for the galvanic protection of the underlying steel, yes.

The Epoxy isn't for toughness at all. it's there because it's easy to apply and is porous, so that he zinc can electrically contact the steel, otherwise it'd be worthless. Epoxy isn't particularly tough at all. It's rather brittle, no matter its formulation. What it is is *rigid*.

The PU is for the toughness. Neither PU or epoxy systems without the correct additives are particularly UV resisting. PU especially yellows horrendously (electronics conformal coatings which are essentially pure PUs demsontrate this well) as it crosslinks to terminal brittleness. The additives are what make both UV resistant, but naturally PU starts off tougher and more impermeable. I say *more*, and remind you of that. Neither *are*. So it takes less additive to keep it more tough, if you see what I mean.

Yes, there are a number of UV resistant epoxies, but the aerospace sector tends to throw PU down on top because it's tougher, not more UV resistant.

And yes, you can put an epoxy topcoat down on top of the zinc epoxy primer, although it won't be as damage tolerant as PU.

Hope that helps :-)

meanwhile

You've been awfully good - but can I ask you to disambiguate one more thing? In this case are you talking about an epoxy that contains zinc, or epoxy as a second layer over a zinc primer? If as a second layer, surely the zinc is already in contact... so you're talking about an epoxy with zinc in, yes?

Very clear.

Very clear. Thanks!

Falanx

The zinc is applied in these cases as a particulate suspended in the primer. In the case of galvanizing or sheradizing, where the zinc is in intimate contact with the iron, a primer can be applied over the top, but that primer only needs to help the paint stick.

In a zinc primer, only a very small amount of the primer is in direct contact with the substrate, and so to make an effective sacrificial coating for years of service, that zinc needs to remain in electrical contact by ion flow, but also..
Whoops, I knew I'd forgotten to mention something...

As the zinc corrodes preferentially to the substrate, it reacts with oxygen and carbon dioxide to form zinc oxide and carbonate, which takes up more space than the zinc itself, filling those pores gradually, making the coating self-healing. The pores only seal shut once all the zinc in that interlinked pore space has reacted, so there's a minor second advantage/use of the porosity of paints

Anyways, yes. I'm on about zinc in primers :-)

rugerben

Holy crap a lot of stuff happened in this thread while I was away!!!

Ok, so powdercoat is porous. But here's a question for you. I have a fair amount of experience with firearms. Several of the finishes used on firearms are porous, such as parkerizing. Now I know that people recommend that you take a parkerized gun, and wipe it down with oil on a silicone rag because the oil is absorbed into the pours of the finish and makes the gun more impervious to the elements. Is that possible, practical, or helpful on something like powdercoating to help protect the metal underneath?

Dr.Deltron

My 2 cents is to spray automotive type clear over the powdercoating.

All you have to do is wipe the frame with DX330 Wax & Grease Remover and spray!

Shiny, like paint; durable, like powdercoating!

NoReg

"Is that possible, practical, or helpful on something like powdercoating to help protect the metal underneath? "

Don't know, the stuff in parkering almost soaks up the oil. It's not that powdercoating sucks, it's just that if a person is specifically looking for something to waterproof their tubes, I am not sure powdercoat is the super star. And all these finishes scratch up easily enough. I Like PC because a local guy will do a frame for 50-60 dollars, and it is pretty eyecatching when he is done. I don't get that from the paint guys. So it is cheap and cheerful, I just don't have any illusions about it being perfect.