smallfry Posted July 5, 2021 Share Posted July 5, 2021 This has nothing to do with Land Rovers, but it could be ! I am in the process of rebuilding and recommissioning our outside toilet. Its a folly project, but very useful. It has a high level cast iron cistern that hasn't been used for years, and is very rusty inside. I have been trying to clean it up with all sorts of potions, but am going to have to give in and get it shotblasted. When its clean, it obviously needs to be coated with something that is suitable for constant immersion in water. I have looked at various epoxy type coatings, but these seem very expensive, so I then thought of galvanising. Seems ideal as the iron needs to be rust free for the zinc to bond. Cistern will be immersed, so coverage will be complete. Will provide long term sacrificial protection, and can be overcoated if required, whereas any sort of paint/epoxy can be compromised, and also has the possibility of missed bits. I see a lot of blurb about hot zinc spraying, and how its "better" than hot dip galvanising in many ways, but this seems to come from those who have an interest in selling the service, rather than independent objective analysis. There is lots of talk about how box sections would NOT need holes drilled for molten zinc to flow and for venting, and how NOT doing this can save weight and money, amongst other reasons. I cannot think why you would NOT want a box section coated internally ??? Surely said item will then corrode from the inside out ? For example, if you wanted a Land Rover chassis or bulkhead coated, what would be the point of just spraying the outside, and not coating the internal areas ? Or am I missing something here ? I can see that very large items could not be immersed and the only option would be spraying, and that items with no closed sections would probably be fine, but apart from that, I cant see that it can be "better". I also dont see that the metallurgic bond would be as good either, in the same way that solder does not work properly if items are not sufficiently heated. So, apart from possible distortion and weld cracking, how can zinc spraying be better ? Does anyone have any experience of it ? Quote Link to comment Share on other sites More sharing options...
miketomcat Posted July 6, 2021 Share Posted July 6, 2021 In my opinion the only rust prevention that works long term is galvanising. That said it's heavy, can block holes and the finish is rough, but it does get everywhere. Hot zinc sprayed is probably the next best thing as it's significantly lighter (it doesn't pool either) and the finish is ripe for painting, but it doesn't go inside totally. Epoxy etc are pretty much the same as hot zinc spray. Though adhesion is questionable which is best. You wouldn't galv a race car chassis because you want it light and smooth equally a garden gate is perfect for galv, your not worried about weight or painting it. Galvanising is generally the cheapest to. Mike Quote Link to comment Share on other sites More sharing options...
missingsid Posted July 6, 2021 Share Posted July 6, 2021 Doesn't galvanising self heal or is that Zinc plating? Quote Link to comment Share on other sites More sharing options...
cackshifter Posted July 6, 2021 Share Posted July 6, 2021 You might also ensure it has plastic fittings inside and in contact as a brass ballcock for example would encourage galvanic corrosion. Quote Link to comment Share on other sites More sharing options...
Gazzar Posted July 6, 2021 Share Posted July 6, 2021 Dipping is crude. But less prone to application error, I had the rims on 109 zinc sprayed three years ago, and the rust is coming through the powder coat. Next time I'm going to soak them in phosphoric acid, blast them, and 2k zinc epoxy them. I think my new compressor set up should cope to do all that. Quote Link to comment Share on other sites More sharing options...
Blanco Posted July 6, 2021 Share Posted July 6, 2021 Is there a concern that (with the rust damage mentioned), the cast might not survive being dipped? The epoxy route would be safer. 1 Quote Link to comment Share on other sites More sharing options...
L19MUD Posted July 6, 2021 Share Posted July 6, 2021 10 hours ago, smallfry said: I am in the process of rebuilding and recommissioning our outside toilet. Its a folly project, but very useful. It has a high level cast iron cistern that hasn't been used for years, and is very rusty inside. I have been trying to clean it up with all sorts of potions, but am going to have to give in and get it shotblasted. Have you tried electrolysis? Quote Link to comment Share on other sites More sharing options...
Gazzar Posted July 6, 2021 Share Posted July 6, 2021 Some of those old castings can be quite crumbly, I'd be reluctant to dip them. Quote Link to comment Share on other sites More sharing options...
smallfry Posted July 6, 2021 Author Share Posted July 6, 2021 14 hours ago, Gazzar said: Dipping is crude. But less prone to application error, I had the rims on 109 zinc sprayed three years ago, and the rust is coming through the powder coat. Next time I'm going to soak them in phosphoric acid, blast them, and 2k zinc epoxy them. I think my new compressor set up should cope to do all that. Rust coming through where the wheel centre meets the rim I guess ? Thats what happened to my RRC Rostyles after I had them powdercoated. Thats one good thing about Hot Dip. All the items are acid dipped prior to dipping even after shotblasting, as the hot zinc will not take to rust, whereas zinc spray will cover it. Went to the galvanisers today so talked about this. They advised not blasting and dipping the cistern because they were concerned about holing it. Quote Link to comment Share on other sites More sharing options...
smallfry Posted July 6, 2021 Author Share Posted July 6, 2021 14 hours ago, L19MUD said: Have you tried electrolysis? No, but I have just read up on it. I am going to get the necessary and give it a go ! 1 Quote Link to comment Share on other sites More sharing options...
L19MUD Posted July 7, 2021 Share Posted July 7, 2021 8 hours ago, smallfry said: No, but I have just read up on it. I am going to get the necessary and give it a go ! Once you have the kit working it is addictive! Best piece of advice I can offer is that it works 'line of sight' so you will need to get an annode inside the cistern being careful it does not touch Quote Link to comment Share on other sites More sharing options...
smallfry Posted July 7, 2021 Author Share Posted July 7, 2021 9 hours ago, L19MUD said: Once you have the kit working it is addictive! Best piece of advice I can offer is that it works 'line of sight' so you will need to get an annode inside the cistern being careful it does not touch Waiting for SWMBO to come home from shopping with some washing soda................ I am going to cheat. Instead of a plastic container I am going to try filling the cistern and dangling the anode from a cable tie inside it and see what happens. What can possibly go wrong ? 🤣 1 Quote Link to comment Share on other sites More sharing options...
L19MUD Posted July 7, 2021 Share Posted July 7, 2021 That should work fine. Just make sure you connect it up the right way round! Quote Link to comment Share on other sites More sharing options...
Arjan Posted July 7, 2021 Share Posted July 7, 2021 Talk to a good galvanizing plant and see what they have to say. Cast iron is different from a chassis etc. Is there is just rust, you may not have to get it blasted as the nasty stuff in the various basins usu. takes care of rust and brings it back to bare steel / iron. I have a bulkhead to be dipped this Fall. Good luck Quote Link to comment Share on other sites More sharing options...
bishbosh Posted July 9, 2021 Share Posted July 9, 2021 Galvanizing and zinc spray are very different. Galvanizing forms a bond with the parent metal so the interface is a mix of zinc and steel (usually) molecules and so doesn't come off easily. Hot zinc spray is just that - effectively a paint coating so definitely not as durable. In my world, things get zinc sprayed if they are too big / awkward to dip. I would think a cast iron item might struggle with the thermal effects of a galv bath, particularly if it is aged and has some rust pitting. It may come out of the bath in more pieces than it went in! That all said, cast iron is very good at resisting rust and actually just blasting it and re-installing it will probably see you out! Quote Link to comment Share on other sites More sharing options...
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