Sound technical content, curated with aloha by
Ted Mooney, P.E. RET
Pine Beach, NJ
The authoritative public forum
for Metal Finishing since 1989
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Cast iron Claw-foot Bathtubs: How to Clean, Remove Rust & Stains, Restore, Re-surface, Recoat
Q. I'm searching for info to restore a cast iron bathtub. The inside does not need re-enameling so I plan to wire brush the exterior paint and apply a primer, then car enamel. The feet have almost a polished look from wire brushing. I have used a brass wheel attached to a Dremel ⇦this on eBay or Amazon [affil links] to clean them up which has worked so well I may just lacquer them! Anyway what I intended to suggest is 19th century jewelry was oxidized black to prevent rusting.
Converting the surface to black iron oxide (Fe3O4) prevents rusting and may give the desired effect. Clean iron is submerged in highly concentrated salt solution (commercially available) for 15 mins at temp. of 290-300 °F then rubbed with a thin film of sweet oil.
B. Rook- Australia
1998
A. Hi B. The black oxide process you are describing is still widely done on things today. Industrial gears, sprockets, couplings and chain are black oxided. Although the corrosion resistance is quite limited, it's an attractive finish that doesn't change the dimensions of the objects like plating or painting does. The same process is widely done on firearms, although people then tend to call it "blueing" rather than "black oxiding". When it's applied to a rough surface it comes out matte black, but when done on a highly polished surface it's comes out closer to a jewel-like navy blue. These are finished surfaces which are not subsequently painted. It might have been used on some of the claw feet of cast iron bathtubs, but I'm not familiar with that. A gun shop can do this process for you.
When you intend to paint a surface, you would instead use a phosphoric acid formulation called naval jelly or rust converter ⇦this on eBay or Amazon [affil links] to convert red rust to that Fe3O4 black rust; this is something which any home owner or hobbyist can easily do, and you can certainly do to the OUTSIDE of your tub if there is any rust. Good luck.
Regards,
Ted Mooney, P.E.
Striving to live Aloha
finishing.com - Pine Beach, New Jersey
RFQ: I live in an old stone terrace house with old cast Iron bath in very small bathroom, the tub is 2 inches shorter than normal bath so replacing is not an option; it has been re-Enameled before but is now badly stained and turning brown but in good condition, but I am having trouble locating somewhere to purchase Enamel from, Can you help me? Any info would be appreciated.
Mr Neil Waters- Wales, U.K.
2002
Ed. note: Sorry, this RFQ is old & outdated, so contact info is no longer available. However, if you feel that something technical should be said in reply, please post it; no public commercial suggestions please ( huh? why?)
A. The thing is, Neil, that the original finish was probably porcelain enamel, more like melted glass than paint -- a ceramic frit (powdered glass) is melted and fused at extremely high temperature onto the cast iron. You can't do that, sorry; so you're restricted to paint (which, sorry, just isn't nearly as good) or finding a porcelain enameling shop to do it for you.
Second best is to hire a professional tub refinisher who can do a good job with premium quality enamel paints. Third best is to purchase specialty touch up enamel ⇦this on eBay or Amazon [affil links] made for that purpose and do it yourself, recognizing that this will not approach the durability of a factory-applied molten coating. Good luck.
Ted Mooney, P.E.
Striving to live Aloha
finishing.com - Pine Beach, New Jersey
Refinishing claw feet of cast iron bathtub
Q. I would like to know how to refinish the claw feet on an old cast iron bathtub making it brass coating. Any information would be helpful.
Robin Bowerspainting - Penhook, Virginia, USA
2001
A. Hi Robin. Brass colored paint and brass plating (real metal) are not the same thing, so you'll need to decide whether you can settle for the paint or must have real brass plating.
Although it is not completely impossible for a hobbyist to do any metal plating at home, brass plating on cast iron would involve sandblasting the cast iron, acid pickling it, nickel plating it (both for shiny appearance and because you can't plate brass directly on cast iron), then brass plating (this is cyanide based), then several well-applied coats of brass lacquer or a 2K automotive clearcoat. In short, if you want real brass plating, realistically you'll need to be able to remove the claw feet and send them to a plating shop.
If you can settle for brass colored paint, get any old paint off as best you can by sandblasting if available to you, or by sandpaper and paint stripper if blasting isn't possible. Then apply a phosphoric acid based naval jelly or rust converter ⇦this on eBay or Amazon [affil links] . Cast iron is porous and you'll probably have rust stain problems if you don't do this. Then do a brass color outdoor paint, brushed or sprayed as you prefer. Topping off with a couple of coats of clear acrylic spray may give a somewhat more metallic look. Best of luck.
Regards,
Ted Mooney, P.E.
Striving to live Aloha
finishing.com - Pine Beach, New Jersey
Tips for restoration of cast iron bathtub
Q. I have gotten hold of a beautiful old cast iron claw foot bath. It needs restoration on the inside and outside. Luckily there are no scratches, just rust and I would love to restore it myself.
Any advice and information on where to get materials and what is required would be greatly appreciated.
Skadi Novajeweler - Sydney, NSW, AUSTRALIA
2003
A. Hi, Skadi. For the outside, you can deal with the rust with naval jelly ⇦this on eBay or Amazon [affil links] before repainting. If the inside is porcelain, you can't really repair this yourself as the coating is more like a melted glass than a paint. But you can probably touch up chips with touch up enamel ⇦this on eBay or Amazon [affil links] , and if there are rust stains, lots of people on topic 8229 swore by hydrogen peroxide ⇦this on eBay or Amazon [affil links] . Good luck.
Regards,
Ted Mooney, P.E.
Striving to live Aloha
finishing.com - Pine Beach, New Jersey
Bath resurfacing
Q. Hi there, I wonder if you can help. I have recently bought an old roll-top cast iron enamel bath and feel that it could do with being resurfaced in some way. I am aware of many bath 're-enameling' products available but know that they are enamel paint rather than real bath enamel which is made of glass & other things. The longest assurance any company can give for their bath enameling products is around 10 years if done properly and looked after with supreme care. I asked a friend who works in a garage whether enamel could be spray painted on using his car painting equipment and he suggested powder coating the bath instead. Does anyone know whether this would work? Could the powder coating stick to the already existing enamel of the bath?
Rachel Andersonhomeowner - Glasgow, Scotland, UK
2004
A. Rachel:
I have had this done on two cast iron sinks. First you will have to find a powdercoater that is willing to take on the project. We first tried to sandblast the surface of the porcelain to roughen it for the coating to adhere to. The first sink took the powdercoating well,but the finish was orange peeled because the sandblasting was done too hard and left the surface of the porcelain too rough. The second sink had some small cracks in the porcelain that allowed out gassing and created large bubbles in the finish. We ended up sandblasting the second sink down to the bare casting,sanding the surface smooth,filling and sanding pits and craters in the casting with a compatible powdercoat filler and then recoated the sink. Overall I am pleased with the results even though after several attempts the second sink still had minor out gassing (pinholes). Sanding the bare casting makes for a nice finish but is very dirty and time consmming.
I hope this helps.
Rodney Walters- Des Moines, Iowa, USA
2004
Q. I have an old victorian rolltop bath and want to sandblast the outside of the bath. Is this possible and will the damp associated with a bathroom cause any problems with rust? Any advice please.
Wayne Crooksself employed market trader - London, England
2004
Cleaning a vintage claw foot cast iron bathtub
Q. How can I successfully clean the inside and outside of a cast iron bathtub. The outside is in it's original black unfinished stage, but has slight rusting from being outside for years. What should I use to clean and restore the outside of the tub, and should it be painted as a final sealant?
Meanwhile the inside has some rust staining on the porcelain surface from someone storing something in the tub, and some minor scratching on the upper rim from hauling it several states up-side-down (rubbing against the truck bed). I've been warned to avoid re-glazing if possible.
consumer of collectibles - Bellingham, Washington, USA
2005
Remove Rust Stains Inside Cast Iron Tub
Q. I recently bought an old claw foot tub. It is in pretty good shape but is stained. The stain is a light red-ish brown, like the dirt around here. I have tried, bleach, soft scrub, Brillo pads and vinegar. No luck yet. Elbow grease does a little but not much.
Ray W [last name deleted for privacy by Editor]- Commerce, Texas
A. As you have just purchased it I'm assuming you have not installed it. Which is good, muriatic acid ⇦this on eBay or Amazon [affil links] will eat through the rust, the porcelain glaze will keep the rest of the metal from being eaten, do this in a well ventilated area as it will give off lots of fumes.
Marc Banks- Elizabeth City, North Carolina
Ed. note: although the ventilation is to protect your lungs, any stainless steel or bright metal in the area can get rusted by the fumes too.
Q. I too have clawfoot bath tub with rust looking stains. Would like to know if the treatment worked on Ray W's bathtub.
Janie Morse- Lampe, Missouri, United States
2006
A. Hi, Ray; hi, Janie.
Although Marc knows his stuff, and his answer probably works, please see letter 8229 first ... because dozens of people swore by the simplicity, economy and effectiveness of hydrogen peroxide for removing rust stains from bathtubs, and I'd hate to see muriatic acid used where a much safer & simpler approach can work. Good luck!
Regards,
Ted Mooney, P.E.
Striving to live Aloha
finishing.com - Pine Beach, New Jersey
2006
A. I had the same dilemma as Ray W in Texas. I tried everything, then I tried powdered Oxygen Cleaner (generic), I mixed 2 scoops in 4 cups of hot water, plugged the tub and let it sit for 15 min., did this twice and it worked with very little scrubbing. Did the trick.
Felice D [last name deleted for privacy by Editor]- Warren, Ohio USA
June 1, 2011
Q. Hi,
I am refinishing an antique claw foot tub that we found in the barn (we just bought our farm). The tub is cast iron and the exterior is terribly rusted. I know how to refinish the interior of the tub (scrub, acid wash, rust inhibitor primer, enamel), but not sure of what to do with the exterior. I don't own a sand blaster, which is the only way I can think to remove all the rust before priming and painting. Is there another way to prep the cast iron surface for priming and painting?
Thanks!
Dedicated D-I-Y-er :) - Appleton, Minnesota, USA
September 30, 2012
Finish coming off tub
Q. I redid my cast iron claw foot tub, it last about 4 yrs and is now peeling. What should I do to get the finish off so I can redo it again? We are putting our home on the market in 2 days and I'd like to have it resolved by then. Thank You for your help.
Jen Phil- Nashville Tennessee USA
July 9, 2016
Hi Jen. You need paint stripper designed to take off whatever it is that you put on :-)
There are some coatings that can only be removed with Aircraft Stripper (methylene chloride) -- but it is truly noxious stuff you can only use with gloves, goggles, and really good ventilation. Hopefully a milder stripper like Citristrip can do it.
Regards,
Ted Mooney, P.E. RET
Striving to live Aloha
finishing.com - Pine Beach, New Jersey
July 2016
Q. I have an old clawfoot tub with deep gouges on the inside. I live outside the USA, so can't get it professionally re-enameled, and there is no local expert on refinishing tubs. Someone here has suggested filling the gouges with auto body putty, sanding it down thoroughly, and then spray painting it with car paint. Will that work? Is there a particular bonding agent or primer that I should try to get, either locally or from the USA?
Gopa Khandwala- Mumbai, India
October 16, 2016
A. Hi Gopa. "You can't make a silk purse out of a sow's ear", and you make thick, glossy, wear-resistant, rock hard, porcelain enamel by spraying a molten glass-like frit at extremely high temperatures; you can't make porcelain enamel from body putty and spray paint :-(
It's not going to be completely satisfactory, but you can only do what you can do. There are 'adhesion promoters' that will hopefully keep the paint from blistering off of the porcelain. Good luck.
Regards,
Ted Mooney, P.E. RET
Striving to live Aloha
finishing.com - Pine Beach, New Jersey
October 2016
Q. Hi- we have a home built in 1904 with original claw foot tub. It is in fantastic condition but there is rust around the filter for the drain. I don't have any way to plug the tub so that I could soak it with hydrogen peroxide [as described in topic 8229]. Is there a paste recipe for this I could use? I need to have something sit on the rust ring I think! Help! Thanks!
Sue Villarreal- Dayton, Ohio, USA
December 26, 2017
December 2017
A. Hi Sue. I'm pretty sure you could thicken hydrogen peroxide with fumed silica (the powder/fluff you see for that purpose in epoxy filler kits). But whether any household product like cornstarch or flour or baking soda can be used without consuming most of the oxidizing power of the peroxide, sorry, I don't know.
Regards,
Ted Mooney, P.E. RET
Striving to live Aloha
finishing.com - Pine Beach, New Jersey
A. Try wallpaper glue (Carboxymethyl Cellulose based); it must work ... Hope it helps, and good luck!
Goran Budija- Cerovski vrh Croatia
December 27, 2017
Q. I have a claw foot tub that's been in storage for about a year. We had it wrapped up pretty well, so the inside is fine, but the outside has a bunch of tiny rust spots all over it. How could we remove those without damaging the tub?
Dominique Devine- Athens, Tennessee USA
July 16, 2018
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