is there any such thing as tough DIY paint?

[bgnukem]

Is this sort of epoxy paint any good?

https://www.taindustrialpaints.co.uk/shop/two-pack-epoxy-metal-paint-cheaper-popular-colours/

[alexnharvey]

Here we go again. My winter bike is off for blasting next week and the epoxy primer is bought and ready to be rolled and brushed on. The blaster thinks I'm mad. He spent about thirty minutes trying to dissuade me from this plan but I want to use this epoxy zinc and I don't have the kit to spray it safely and I don't care much how it looks, I just don't want it to rust any more.

[Brucey]

if the epoxy primer is any good that is what will protect the metal. It can be overpainted with a suitable base coat, wet flatted, and given a topcoat if you like. All the topcoat does is look pretty, if you value that.

cheers

[fastpedaller]

What Brucey says ^^^^^^^
The epoxy should do a good job for the primer coat. FWIW I've used 2 pack paint as a gloss coat (not on a bike) and if was difficult to put on because the thinner it's applied the quicker it dries. I used a brush, and if spreading it out (like one would with a slow-drying enamel) it was drying immediately. If you've ever used the thixotropic household paints, the application is similar in that it likes to be put on in what would normally be considered a thick coat. My advice FWIW is that you'll need to do this in a well-heated area at this time of year, and allow the frame several hours to reach that temperature before you start painting - any moisture (especially your breath) will condense on a cold frame and prevent the paint adhering properly. Too dangerous to spray it (ingestion of spray hazardous to health). You may find it easier/better to use a brush because a roller is more suited to flat surfaces.
ETA you should be able (after a good drying time) to follow the primer with any oil-based paints eg undercoat and gloss as there shouldn't be a compatibility problem. 2 pack/epoxy can't be put over oil paint, but oil can be put over epoxy.

[alexnharvey]

Yeah, the blaster hasn't seen how rough the bike is currently! Given the heavy rust pitting it would need lots of filling and sanding to get a smooth surface for a fine finish anyway.

[Brucey]

lets hope that the frame cleans up OK and hasn't actually got holes in the metal which the rust is currently hiding......

BTW if the paint is mostly sound and the corroded area is relatively small, I might forgo the blasting altogether (unless it is dirt cheap) and treat/paint locally. I shall be interested to see how you get on. I'm sure that any before/during/after photos would be of interest to folks here.

cheers

[alexnharvey]

Brace yourselves.

I think the steel is to9 thick to have rusted through! I did consider local treatment but the pitting is deep and there are smaller defects elsewhere all over the frame. In particular I thought the chainstays BB bridge area would be very to get cleaned up.

I did buy a couple of drill attachments but I started to look like taking half a day or get back to bare metal and I'm prepared to spend 20 quid with the bonus that he'll keyphos afterwards too.

[Brucey]

it is only about 10% of the frame which is bad though....?

FWIW I have a spot shot blaster which will clean up small inaccessible areas (eg around the chainstay bridge). You will need a decent compressor to run it (and probably to buy some media too), but you are welcome to borrow it if you want.

cheers

[alexnharvey]

Yes, lack of a compressor and proper work space is a big problem for this project. Maybe I just need to get the angle grinder with wire brush on it and see what remains hard to reach after that.

[Brucey]

FWIW I have been known to use the blaster in the garden, using kiln-dried sand as the media. If I don't recover all the media, it is no big deal, because it is cheap enough and the lawn gets a free top-dressing...

cheers

[Tilley]

The few times I spray painted bike frames in the fashion you are referring I applied a clear lacquer over the paint finish to provide a more durable finish.

[alanesq]

I have had such bad results with any painting I have ever attempted to do that I eventually just gave in and even painted my car with standard metal paint and a brush - lol

But recently I watched this video: https://www.youtube.com/watch?v=x7onZGqrYyY&t=482s
I wish I had seen this video many years ago as I strongly suspect that this answers why I have never had any success.

BTW - The whole series of videos is well worth a watch

[alexnharvey]

Half an hour with a polycarbide rust stripping disc on the angle grinder did not make as much impact on the rusty areas as I expected plus the pitting is quite deep. Further there are numerous bubbling areas around the rest of the frame. I think I'm going to send it off for blasting...

[Brucey]

if you want to shift rust with an angle grinder then IME one of these is the thing;


twisted knot wire cup brush for angle grinder

When this type of brush is new the wire strands have jaggy ends and you can damage sharp edges on the work quite easily. Once the brush is a bit more worn it is less likely to damage anything steel but it is still a very aggressive tool. It of course won't reach into all the corners on a bike frame but you can do 80-90% of a frame in about half an hour if you want to.

Obviously you won't chase rust out of pits this way, but then you won't by blasting either, not on a bike frame, not unless the media is so small that it will go down the pits, right to the bottom. And it never is. On hefty lumps you can 'pressure blast' with coarse and aggressive media and this can be aggressive enough to remove the entire surface which includes the rust pits. If you try and use this method on a bike frame it simply won't survive the treatment. If you use a microscope on a blasted surface in something thin-walled like a bike frame, what you might see is that the pits are not very evident simply because of the distracting effect of the new surface texture. If there were pits before, they will still be there; if you leave such a blasted part anywhere that isn't absolutely bone dry, it'll start corroding again and the corrosion usually just climbs back out of the (still rusty in the bottom) pits.

So arguably it doesn't matter how you try and remove the rust on a bike frame; if there is pitting then the only thing which will prevent rust breaking out again (from the pits) is a chemical removal/passivation/conversion treatment of some kind. If you use a good treatment of this type then this is the thing that stops rust from breaking out again, not the cleaning treatment itself.

cheers

[alexnharvey]

Yes, that's one of the attractions, that they'd phosphate coat it afterwards. I have been toying with making up a phosphating solution by adding zinc to some rust converter to make zinc phosphate.