Author Topic: Which brush-on metal primer to use?  (Read 3717 times)

Which brush-on metal primer to use?
« on: 25 June, 2017, 04:02:15 pm »
On my (2 month-old) Brompton a whole strip of paint has peeled off from the frame on one side of the seat clamp retainer, looks like down to the bare metal:





I've just ordered the Brompton-recommended touch-up paint (they no longer make their own touch-up paint), which for my British Raching Green colour is Humbrol Brunswick Green enamel gloss, then Humbrol Matt Lacquer to finish:

https://www.humbrol.com/uk-en/3-brunswick-green-gloss-50ml-enamel-paint.html

https://www.humbrol.com/uk-en/humbrol-matt-clear-125ml-bottle.html

Because it's gone down to the bare metal, though, I'm assuming it would be wise to use some sort of brush-on primer, especially as this area is probably prone to wear, as it's where the frame meets the suspension block - I've no idea which one to use, though - does anyone have any recommendations?

Also, any other tips for prepping/painting (e.g. sanding?)? Thanks!
Old enough to know better, but young enough to do it anyway

Torslanda

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Re: Which brush-on metal primer to use?
« Reply #1 on: 26 June, 2017, 07:36:28 am »
If you could stand being without it then take it back!

They charge enough for the damn things.
VELOMANCER

Well that's the more blunt way of putting it but as usual he's dead right.

Re: Which brush-on metal primer to use?
« Reply #2 on: 26 June, 2017, 08:40:39 am »
If you could stand being without it then take it back!

They charge enough for the damn things.

I might take it into Warlands in Oxford (where I bought it from) and see what they say...
Old enough to know better, but young enough to do it anyway

Torslanda

  • Professional Gobshite
  • Just a tart for retro kit . . .
    • John's Bikes
Re: Which brush-on metal primer to use?
« Reply #3 on: 26 June, 2017, 03:49:29 pm »
I'm fairly certain the Brompton have their frames powder coated.

This should not peel. End of.

The clamp isn't in a position where it is easily abraded which leads me to believe it's a quality control problem...
VELOMANCER

Well that's the more blunt way of putting it but as usual he's dead right.

Re: Which brush-on metal primer to use?
« Reply #4 on: 26 June, 2017, 04:08:26 pm »
The frames are indeed powder coated. The rubber suspension block  does butt up against that part of the frame, so I'd expect to see a little bit of general wear after extended use, but not a whole section of powder coat peeling off after only a few months light usage.
Old enough to know better, but young enough to do it anyway

Re: Which brush-on metal primer to use?
« Reply #5 on: 26 June, 2017, 04:13:20 pm »
Definitely return it, that's not acceptable.

Re: Which brush-on metal primer to use?
« Reply #6 on: 26 June, 2017, 09:27:10 pm »
The frame on my bakfiets is also AIUI powder-coated, and small paint strips have also lifted along the thin edges of components like that; I assume what happens is that the primer and paint don't adhere to the sharp edges properly, and this allows the protective layer to be breached and the paint to lift. OTOH I would have thought it's unlikely to cause any great grief even in the medium term; it's not like it's a thin-walled tube or the like, so corrosion is unlikely to cause any damage other than cosmetic.

If you do end up having to try and fix it I'd use a wire brush and/or fine-grit emery paper to make sure there was no rust under the paint at the edges of the bare patch, then just use whatever zinc primer I could find most cheaply at Halfords before touching up. I keep meaning to do this for the bakfiets, but as this would mean stripping the bike down I've not yet got round to it...

Re: Which brush-on metal primer to use?
« Reply #7 on: 27 June, 2017, 01:29:56 pm »
Thanks Jakob, I'll see if I can get some zinc primer.

BTW this is the not very helpful response from Brompton:

I'm afraid that while this particular example as manifested fairly quickly, we cannot reasonably cover wear and tear to the powdercoat finish - or any of the other finishes - on the bike. Bicycles in general, but particularly Bromptons, are tools for a job and will inevitably take knocks and undergo cosmetic and mechanical wear through their intended use. This is stated in our warranty terms (https://brompton.zendesk.com/hc/en-us/articles/115000554605).

The steel we use is treated against corrosion to prevent undue structural issues, however to prevent localised cosmetic corrosion we do recommend sealing off worn powdercoat either with a clear lacquer, or enamel paint from a modelling shop. The Pantone code for our Racing Green is 357 C
Old enough to know better, but young enough to do it anyway

Re: Which brush-on metal primer to use?
« Reply #8 on: 27 June, 2017, 02:34:35 pm »
if it were almost anywhere else on the frame then yes maybe the paint ought not to have come off and yes touching it in would be a great thing to do. But where that wear/damage is , I think you might be wasting your time doing very much there at all; I think the paint will wear off that surface whatever you do to it. 

If you take a look at a few well-used Bromptons you will soon see if any of them have their paint intact at this point. I suspect that none of them will be wear-free at this point, but this is something you can check easily for yourself.

The first blemish on anything new is always painful but when all is said and done it is a tool and it is there to be used, not set in aspic.

It may be worth trying one of the usual schemes to prevent creeping damage in high-wear areas, e.g. applying tape to the area. I don't think that will last either, in fact, but it may help rather than hinder.

BTW the paint will almost certainly have a RAL code.

cheers

Re: Which brush-on metal primer to use?
« Reply #9 on: 27 June, 2017, 03:17:51 pm »
I'm fairly certain the Brompton have their frames powder coated.

This should not peel. End of.

The clamp isn't in a position where it is easily abraded which leads me to believe it's a quality control problem...

Agree, my 15 year old Brompton is still good at that point. It's had a fairly easy life compared to its heavily used stable mate bought at the same time which I recently sold on ebay for c. £500:



Scrubbed up nice:



Note original saddle put back for the sale.  I was quite good at touching up with hammerite gloss, which took very well if done immediately but fairly sure that bit wasn't touched up ever.
Move Faster and Bake Things

Re: Which brush-on metal primer to use?
« Reply #10 on: 27 June, 2017, 04:55:34 pm »
if it were almost anywhere else on the frame then yes maybe the paint ought not to have come off and yes touching it in would be a great thing to do. But where that wear/damage is , I think you might be wasting your time doing very much there at all; I think the paint will wear off that surface whatever you do to it. 

If you take a look at a few well-used Bromptons you will soon see if any of them have their paint intact at this point. I suspect that none of them will be wear-free at this point, but this is something you can check easily for yourself.

The first blemish on anything new is always painful but when all is said and done it is a tool and it is there to be used, not set in aspic.

It may be worth trying one of the usual schemes to prevent creeping damage in high-wear areas, e.g. applying tape to the area. I don't think that will last either, in fact, but it may help rather than hinder.

BTW the paint will almost certainly have a RAL code 357 C, but not sure that actually helps. The Humbrol Brunswick Green I have looks like it should be quite a good match.

cheers

I've seen a number of well-used Bromptons that have just minor paint wear in this area after years of use, have not seen any that have had a whole strip of paint come off like this, though.

I have already applied hard-wearing clear helicopter tape to all the areas of the frame which are susceptible to rubbing by the cables or chain, I did that shortly after purchase, following a guide I found on the web. Those areas seem to be holding up well, but I wouldn't expect any wear after only about 100 miles of use anyway.

I don't know about a RAL code, but Brompton said their Racing Green has the Pantone Code  357 C, not sure that this actually helps in finding a better paint match, though.

Anyway, it's looking like I'm going to have to deal with this myself, as Brompton don't seem to want to help, and I don't like the idea of leaving that part of the frame as bare metal, so am back to looking for a suitable primer to use before applying the paint, still a bit unsure which zinc primer to get, as there seem to be lots of different types...

Old enough to know better, but young enough to do it anyway

Re: Which brush-on metal primer to use?
« Reply #11 on: 27 June, 2017, 05:54:17 pm »
if powder coat fails en masse it usually means it isn't adhered to the base metal quite well enough. Powder coating is prone to being like this anyway, and it isn't unusual for the coating to have lifted next to a damaged area also.  This means that unless the paint surface is perfectly sealed all round, corrosion will easily set in and cause bubbling and further lifting of the powder coating.

So yes the bare area will benefit from a decent primer but that won't necessarily stop corrosion if the powder coating isn't adhered well enough.

cheers


Re: Which brush-on metal primer to use?
« Reply #12 on: 28 June, 2017, 01:54:30 pm »
I purchased some brush-on Isopon / "David's" Zinc 182 anti-rust primer in the end: http://www.bhl.co.uk/isopon-upol-z182-s-zinc-182-anti-rust-primer-250ml.html

I presume this needs to be left to dry/cure for a few days before applying paint? Should one application be enough and does it need to be sanded down at all before applying paint? Thanks

Old enough to know better, but young enough to do it anyway

fruitcake

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Re: Which brush-on metal primer to use?
« Reply #13 on: 28 June, 2017, 02:11:37 pm »
Rubbing down the steel should help adhesion and make your paintjob last longer.

Sanding the primer coat flattens the surface which in turn enables your topcoat to be flat.

The rattlecan version of Zinc 182 can be sanded when it's no longer soft. This takes a couple of days, though the time is determined by humidity and temperature. I expect the brush version will take longer to harden as the coat will be heavier. If you start sanding the primer and it crumbles, rub it down and start again, and leave it longer next time.

I'm experimenting with DIY paint jobs and writing up the results at this page - though for the retouching you're doing, you don't need to worry about most of the info there.

Re: Which brush-on metal primer to use?
« Reply #14 on: 28 June, 2017, 03:17:00 pm »
Thanks, though the bare steel exposed is showing no corrosion yet and I think is meant to have been treated in some way by Brompton against rust, so not sure whether it will need/should be sanded first or not? What grit paper should be used for sanding the bare frame and)or primer? When the primer is ready for painting with the Brunswick Green enamel, should one coat be enough? If not should this be left a few days before applying another coat? How long should I wait after a final paint coat before applying the Matt clear lacquer? Thanks!
Old enough to know better, but young enough to do it anyway

Re: Which brush-on metal primer to use?
« Reply #15 on: 28 June, 2017, 03:28:36 pm »
Given where it is, and what that part of the frame does - a resting / impact point for  the suspension block, I think you will be repeating the prepping / priming / painting process many times, simply 'cos no applied re-finish is likely to last.
I have a 2013 Brompton and 98% of the original powdercoat is still present in that area - two chunks, smaller than pin-heads are missing - but the mileage on my Brommie is relatively low.
FWIW, the weasel alarm went off here, unprompted, when I read the response you received from Brompton.
If it were me, I'd probably not bother with re-painting - give it a dab of something like LM grease (or something similarly heavy) every few weeks, just to act as a corrosion inhibitor.

fruitcake

  • some kind of fruitcake
Re: Which brush-on metal primer to use?
« Reply #16 on: 28 June, 2017, 03:33:58 pm »
Thanks, though the bare steel exposed is showing no corrosion yet and I think is meant to have been treated in some way by Brompton against rust, so not sure whether it will need/should be sanded first or not? What grit paper should be used for sanding the bare frame and)or primer? When the primer is ready for painting with the Brunswick Green enamel, should one coat be enough? If not should this be left a few days before applying another coat? How long should I wait after a final paint coat before applying the Matt clear lacquer? Thanks!

Perhaps put those questions to Brompton, since they batted it back to you by telling you to buy Humbrol. Reasonable to expect them to follow up with advice of the kind you're seeking, in the circumstances. They'd know whether they've applied any anti-corrosion treatment.

Or perhaps just give it a go with the paints, following the directions on the tin, and see what happens.

Generally the longer you leave each coat to harden, the better the results, but bear in mind that model shop paints won't match the performance of a factory coating. As Jurek says, paint will get a hammering at this location - so I wouldn't be too disappointed if the Humbrol flakes off.