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  1. #1
    Join Date
    Oct 2007
    Location
    Louisiana (Cajun Country USA)
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    141

    Default Cast Iron Toilet Tank...What Would You Do?!

    I would like to present you guys with a situation and ask what you would do if you were in this situation.

    I had 8 legs for 2 claw foot tubs powder coated recently. During the process, 1 of the 8 legs cracked. I asked the powder coating place about this and they said it was already there. I told them it wasnít. They said they didnít drop it and said they only thing they can imagine is that it had a hairline crack in it already and that during the baking process, the iron expanded and it cracked. I was planning to leave my cast iron toilet tank with them to have it done, but Iím having second thoughts now.

    I have the chance to purchase another wall hung toilet tank (used of course), although not cast iron. I was thinking of purchasing the tank as a back-up and proceeding with having the cast iron toilet tank powder coated. If something goes wrong in the process, I have the back-up tank to use. If it were you, would you take the risk?!
    peace,
    Sophie

  2. #2
    Join Date
    Jan 2008
    Posts
    1,093

    Default Re: Cast Iron Toilet Tank...What Would You Do?!

    I don't believe in risking ruin of hard-to-find or historic items. However, as may have been the case with the tub leg, an item can have unseen damage waiting to bite you later. You need to assess what you want as the end product before you start. Powder coating is an excellent finishing process, but it is not the only surface finish, it is not always the best process for everything, and it is not needed here.

    Cast iron, especially the old items where there was far less control and testing of the raw ingredients, is a strong but sometimes temperamental metal. Just the process of casting and cooling induces stress risers which stay in the metal till it fails.

    Powder coating requires heating of the item to bond the powder to it after the powder has been electrostaticlly attached. This reheating is particularly hard on cast iron as it exacerbates the original stress risers that till then hadn't failed.

    Were I trying what you are, I would not want powder coating for the finish because of that risk. If I were adamant on it, I would first have the item crack-tested. There is "Xyglo" testing which uses fluorescent dyes, and there is "Magnafluxing" which uses iron filings and a magnetic field to search for cracks. None of these require enough heat to place the casting at risk. Both can be accessed through automotive racing or restoration shops where these processes are used to check cast crankshafts for integrity before machining them. Neither is cheap, and Magnafluxing is the better of the two but it requires experience to assess the resulting patterns properly.

    But I would not be trying what you are for this. Rather I would go to the conventional painting processes that were used on cast iron successfully for ages. There is no need to powder coat and it is neither historically accurate nor appropriate for an item shaped like this where thin castings, comparatively sharp radius corners, and metals of unknown and likely impure iron were used to make it.

    If you're determined to go ahead with the powder coating you need to use a shop that will heat the tank very slowly, thus taking more of their oven time which is one of most costly parts of the process. That will also mean they cannot do other work while they are going slow with yours adding even more cost. And I'd "Xyglo" the tank beforehand- in this case "Magnafluxing" would be overkill though it may be the only locally available option.

    Phil
    Last edited by Mastercarpentry; 04-22-2012 at 10:29 PM.

  3. #3
    Join Date
    Oct 2007
    Location
    Louisiana (Cajun Country USA)
    Posts
    141

    Default Re: Cast Iron Toilet Tank...What Would You Do?!

    Quote Originally Posted by Mastercarpentry View Post
    But I would not be trying what you are for this. Rather I would go to the conventional painting processes that were used on cast iron successfully for ages. There is no need to powder coat and it is neither historically accurate nor appropriate for an item shaped like this where thin castings, comparatively sharp radius corners, and metals of unknown and likely impure iron were used to make it.
    Thanks for your insight. I'm still undecided on what I will do. However, this tank was never painted. It is porcelain coated. Oddly enough, the inside of the tank is in worse condition than the outside of the tank. There are spots inside where the porcelain has been chipped away and it is rusting. I did speak to a gentleman some time back about the "refinishing" process he does and I remember him telling me he would not do the inside of the tank, only the outside. I do plan to contact him again and discuss it with him further.
    peace,
    Sophie

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