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DIY Cast Iron Tub and Sink Repair: How to Fill and Patch

Living in Seattle on a grad school budget meant having to sometimes settle for a lifestyle very different from the one I lived in Missouri only a few years ago.

With Seattle’s booming tech industry, housing on a grad school budget usually implies lots of roommates or ultra-tiny studios (some students I knew even lived in apartment buildings where kitchens and bathrooms were shared by a whole floor!) I was very lucky to find an old apartment building in the old downtown neighborhood of Seattle, just two blocks from Pike Place Market, where I was able to rent a small- but not “micro” –  studio apartment in my price range. Though it had lots of drawbacks, the high ceilings and Puget Sound views, along with a lot of vintage charm, made it a great find.

How to patch and fill cracks or rusted sections of cast iron rubs and sinks

The Kitchen Eyesore

When I moved in, my sink had a few rusty spots. Unfortunately, the tiny kitchen was so small that it required boat-galley-kitchen equipment, and the company that produced the sinks for my building had long since gone out of business: so no replacement. Most of the kitchens in my building been “upgraded” to miniature versions of industrial kitchen equipment – stand-alone stainless steel sinks, etc. And while my apartment manager was willing to do the same “ugrade” (ugly + upgrade)  on my apartment,  I was afraid I’d lose the lovely vintage feel in my unit that made my space feel so much like home.

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DIY rusty sink repair and patch
The requisite “before” photo

So, I decided to try taking a stab at repairing the old cast-iron sink in my apartment kitchen. The farmhouse at Hawk Hill House had a vintage sink in the basement that had been badly damaged. I always wanted to repair it and bring it up to install in the mudroom but I never took on the project – always scared I’d make the damaged sink look worse than it did already. Commercial estimates to repair the damage to that farmhouse sink ranged upwards of $400, so that lovely old sink remained in the basement until I sold the property in 2016.

This time, as my sink began to degrade further, I decided it was now or never – I could either try repairing the rusty spot on my cast iron sink, or I could give up and let the apartment management drop an ugly modern sink into my 120-year-old apartment.

To repair my sink I just needed a few items

Two essential supplies that made this a quick DIY:

metal filler will fill holes in the cast iron, and good enamel paint will cover the filler with an enamel coating

Step 1: Remove Rust from Sink:

The first step was to clean the sink and scrubbed the rusty parts. I used a toothbrush to clean around and IN  the rusty portions, removing any and all loose debris.

Food grade citric acid can be helpful to eat away rusted portions without scrubbing, just mix powdered citric acid with a bit of hot water, dissolve, and saturate the rusty area. Ideally, you can remove all rust for the “perfect fix,” but if you are just looking to get a few more years out of a cast iron sink with a death wish, you can do your best, leave some rust, and expect to need to repeat this process or replace eventually.

Before: DIY rusty sink repair and patch

Step 2: Allow to Dry and Protect Surrounding Surfaces

Once your rusty spot has been de-rusted as much as possible, allow the area to dry thoroughly from any water used during cleaning and lay down a layer to protect your countertop.

In these photos, you can see that I use some scraps of marble finish contact paper as an easy way to protect large surfaces from any stray epoxy or paint. Similar to taping the trim in a room before painting, protecting the surrounding surfaces both made the job easier and guaranteed a better-looking finish.

protect surrounding areas with tape or contact paper

Step 3: Insert Metal Filler

Before the outside could be refinished, I needed to fill the gaps in spaces where rest had eaten through the porcelain and cast-iron. Thankfully, I wasn’t the first person to need to patch and fill corroded metal – and this Devcon epoxy metal filler made the process easy. Working in about three stages – I had to allow each layer to dry before it added another in order to fill this very deep gap – I was able to completely fill the gaping hole in this rusted cast iron sink.

Once dry, this metal patch is as hard as metal, and once the epoxy appliance paint is added it will be equally as waterproof. It’s a great choice for a DIY vintage cast-iron sink repair.

layer filler into the damaged part of the tub or sink


Step 4: Sand and Finish Hardened Cast Iron Filler

Once the metal filler is completely dry (cured?) It’s time to file it down to a smooth finish. Once dry, it’ll lighten in color and look a little something like this:

allow the filler to dry completely

Begins sanding the metal filler down to a smooth finish using progressively finer sandpaper.  I’m gonna make a DIY confession here: I rushed this portion of the job and I regret it. I didn’t have the range of sandpaper needed to sand down the bumps and add an ultra-smooth finish. But I was impatient, so I continued to the next step.

After the cast iron filler dries, sand it and prepare for painting


Step 5: Clean Sanded Filler

It’s very important to remove all of the fine particles created in the sanding process. You can wash the area and allowed to dry – or clean with a cloth soaked in rubbing alcohol. The alcohol evaporates quickly, allowing you to continue on to the next step within a few minutes.

Step 6: Paint with Appliance Epoxy

Appliance epoxy is not regular paint – it’s super heavy duty paint with an ultra hard finish that can stand up to just about anything except ultra high heat (special appliance paint is sold for repairing enamel chips on stoves). It’s a perfect choice for minor repairs on vintage cast-iron or porcelain bathtubs and sinks. In this case, it’s a cover-up that will improve the look and add a few more years of usability to my doomed sink.

Use only special enamel paint for covering the patch- it's water resistant and has the sheen of a cast iron tub finish

Using a small paintbrush, I mixed the paint together and added a waterproof white coating over this gray metal filler.

After the paint dried, I was able to peel away the contact paper revealing and unscathed countertop.

Project Complete

While not exactly a rags-to-riches story, this functional DIY did add a few more years of life to my adorably unique vintage kitchen and its irreplaceable custom sink.

carefully apply paint to the tub or sink, over the patched portion
How to patch and fill cracks or rusted sections of cast iron tubs and sinks


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Friday 7th of May 2021

Thank you so much!