Help DIY painters / chemistry nerds

[K3nny]

Howdy all,

I'm planning on repainting an aluminium frame soon, but need clarity on the bare aluminium prep step prior to painting. 'ETOE' youtuber specifies the need to completely eliminate any oxidation and links an aluminium degreaser, active component ammonium hydroxide 29%; This appears to be an ammonia and water solution at a specific concentration? Can't seem to readily find pure ammonia, supermarkets/bunnings list 'cloudy ammonia', which has a soap component added. Auto shops/bunnings stock aluminium specific cleaning products, which appear to be acid based.

Question 1: Anyone tried/recommend just going from sanding and degreasing (IPA or equivalent) immediately to paint, or does oxidation occur too rapidly to avoid?

Question 2: Otherwise, anyone know where to easily get pure ammonia, of sufficient concentration to achieve 29%?

Question 3: Anyone tried/recommend going with cloudy ammonia? Seems like it might de-oxidise and degrease in one step.

Question 4: Anyone tried/recommend an acid based aluminium cleaner? Supercheap Auto has 'Septone Ali Brite', which is advertised as industrial grade and "...removes corrosion products and oxide films with minimal attack on the substrate and reduced localised pitting."... which sounds promising.

TIA

[Jean]

I've mostly painted steel and carbon fibre, so I won't profess any particular expertise. But I suspect that Septone product will be a good substitute for what ETOE recommends. Painting aluminium seems highly reliant on etching, either mechanically by a slightly rough (sanded) surface, and by using etching primers. With that primer down, you can use normal paints without any problem, as long as they are compatible.

Going to a proper auto paint supplier for a chat might also be a good idea. They usually cater to a DIY crowd (car tinkerers on a budget, of which there are many) as well as the pros, and can be most helpful.

[ldrcycles]

That's overkill IMO, I've done aluminium by just sanding immediately followed by a wipe down with acetone, then straight onto etch primer and haven't had any trouble.

At my (non bike related) work, we just sandblast, blow off the dust with an airgun and then use a zinc hammertone paint straight onto it. That works for 3-5 years in corrosive environments.

[Andy01]

Howdy all,

I'm planning on repainting an aluminium frame soon, but need clarity on the bare aluminium prep step prior to painting. 'ETOE' youtuber specifies the need to completely eliminate any oxidation and links an aluminium degreaser, active component ammonium hydroxide 29%; This appears to be an ammonia and water solution at a specific concentration? Can't seem to readily find pure ammonia, supermarkets/bunnings list 'cloudy ammonia', which has a soap component added. Auto shops/bunnings stock aluminium specific cleaning products, which appear to be acid based.

Question 1: Anyone tried/recommend just going from sanding and degreasing (IPA or equivalent) immediately to paint, or does oxidation occur too rapidly to avoid?

Question 2: Otherwise, anyone know where to easily get pure ammonia, of sufficient concentration to achieve 29%?

Question 3: Anyone tried/recommend going with cloudy ammonia? Seems like it might de-oxidise and degrease in one step.

Question 4: Anyone tried/recommend an acid based aluminium cleaner? Supercheap Auto has 'Septone Ali Brite', which is advertised as industrial grade and "...removes corrosion products and oxide films with minimal attack on the substrate and reduced localised pitting."... which sounds promising.

TIA

Trust me - you want absolutely nothing to do with pure ammonia.

I worked in ammonia plant (maintenance manager for 4 years and plant manager for 5 years) and pure ammonia (well, 99.65%) is so volatile and toxic that it can kill you.

Cloudy ammonia is only 5% ammonia diluted with water (so called aqueous ammonia) and that stuff will take you breath away and cause most people to tear up. A lung full of the full strength stuff causes you to tear up so badly that you can't see a thing and makes you feel like you are suffocating - I experienced it many times in my time in the ammonia plant - very nasty. I have unfortunately seen a number of people be taken away in ambulances after being exposed to pure ammonia.

Ammonia is a VERY strong base or alkali substance - almost as strong as caustic, which effectively "eats" aluminium, so I am not sure I would recommend using it for paint prep unless you are experienced in doing so.

As suggested above, just wipe down with a good paint prep degreaser a couple of times (using a lint-free rag/cloth) and then a final wipe with acetone

If you do manage to get hold of ammonia at any decent concentration (perhaps from a mate in industrial refridgeration ?) be VERY careful about diluting it with water - the reaction is VERY violent as it causes massive expansion of the ammonia so it gives off a lot of vapour and/or pressure and also heat (a far more violent reaction than pouring water on pool acid for example). I strongly recommend avoiding it.

[Philistine]

'ETOE' youtuber specifies the need to completely eliminate any oxidation and links an aluminium degreaser, active component ammonium hydroxide 29%;

Your you tuber has given you a bum steer. Unless you work in a vacuum with scuba gear to keep you alive, you cannot eliminate oxidation from aluminium - nor should you want to! When you handle a lump of aluminium, it has a thin film of oxide (so thin you can see the aluminium through it) on every surface. If you manage to scrape it off it just reforms. This is the reason aluminium is so corrosion resistant.

All you should really care about is whether or not the paint you apply will adhere to the aluminium oxide, and the same factors are in play as for any other paint job. Paint doesn't like oil, grease, or loose bits. Avoid these and you'll be sweet.

[K3nny]

Thanks for the info and warning so far. Seems like degreasing and etch primer is the way to go for aluminium. Could someone also kindly advise for raw carbon fibre:

Question 1: What's an appropriate degreaser? I've been worried about effecting the resin and have been using lightly soapy water so far, but from what I've read, I think I could use IPA?

Question 2: If I were going for a color and clear coat finish, what type of primer would I use?

Question 3: If I was going for a naked carbon look (this was how the forks were), can I go straight to a 2K clear coat, or should I also prime it first?

Thanks again, in advance.

[Duck!]

For carbon give it a light sanding all over then wipe off with acetone. If clearcoating just go straight over it with a polyurethane finish, which will be quite durable. If applying a colour, same initial prep, prime with an epoxy primer, then it's the same as painting anything else.

[paulcxw396]

For carbon give it a light sanding all over then wipe off with acetone. If clearcoating just go straight over it with a polyurethane finish, which will be quite durable. If applying a colour, same initial prep, prime with an epoxy primer, then it's the same as painting anything else.

Good advice!

[Andy01]

This was a pretty old thread but 29% ammonia is not pure ammonia.

Pure anhydrous ammonia is 99.96% and is EXTREMELY dangerous. At those concentrations is is extremely volatile and has to be stored either in a pressure vessel or at -25°C and atmospheric pressure.

I am not aware of any ammonia solutions available to the public at 29% - even this concentration would be very dangerous.

General cloudy ammonia (as mentioned more than a year ago in this thread) is around 5% anhydrous ammonia and 95% water - and even that will bring a tear to most people's eyes.