Working with an Oversized Cast Iron Sink

Installing and leveling an oversized cast iron sink is a breeze with these simple tips from WatermarkFixtures.

Cast iron sinks are a timeless addition to your kitchen. A durable fixture, vintage-inspired cast iron sinks – made of porcelain enamel hand-applied to cast iron – can last a lifetime. They feature a smooth, glossy finish that is easy to maintain and comes in a variety of colors. Cast iron sinks come in a variety of mounting styles; however, mounting them takes extra consideration. The weight of a cast iron sink means that they require extra support for most installation types. For oversized cast iron sinks, you’ll need to take special care to ensure that it is supported and completely level. A sink that is not level can cause water to pool or have a lip that does not sit flush with your countertops.

What’s Up With My Sink?

Sometimes, cast iron sinks need a bit of extra work to sit completely level. To understand why, it’s important to know how cast iron sinks are made. Cast iron sinks are created by pouring molten cast iron into a mold. The raw cast iron sink then has the enamel (or frit) hand-applied to it. The sink is then fired to turn the enamel into one smooth, continuous layer. The refiring of the sink can cause some inconsistencies in the final product, leading to a sink that has some variations. These variations can cause the sink to not sit flush on your countertop. However, we know just how to help you fix this issue! 

How Do I Fix an Uneven Sink?

Ensuring that your oversized cast iron sink sits flush takes a few tools and a little bit of shimmying. You’ll need a level, water, a router, and shims. Carefully place your cast iron sink into your countertop. Check it with a level from side to side and then again, from front to back. Pour water into the sink to check for areas of pooling (make sure there’s a bucket underneath!). Use wood shims to adjust the sink. For example, if water is pooling at the front of the sink, insert a shim or two along the front edge. Pour more water into the sink to see if it’s still pooling. If it is, keep shimming! Once water is no longer pooling, note which sides to which you’ve added shims. Remove the sink from the countertop. Grab your router (or have your plumber grab their router) and rout the sink on the sides without shims. When you place your sink back into your countertop, it should now be flush and level. Check it again from side to side and from front to back. And that’s it! Your oversized cast iron sink is now both beautiful and functional!

Check out our easy to follow instructions and walkthrough video below.




  1. Place the sink into the countertop.
  2. Place the level in the center of the countertop running left to right.
  3. Check the levelness of the sink from left to right.
  4. Place the level in the center of the countertop running front to back.
  5. Check the levelness of the sink from front to back.
  6. Pour water in your sink to check the area where it is pooling. 
  7. Lift the sink slightly and slide a shim in place. 
  8. Check the drainage of the sink again by pouring more water into it. 
  9. Repeat this process until water is no longer pooling into the sink. 
  10. To set the countertop in place, rout along the sides that you have no shimmed. For example, if you’ve placed shims along the front edge of the sink, rout the back and sides of the countertop. Leave the front of the countertop as is, so that when the sink is placed back into the countertop, it will sit level.

Check the levelness of your sink again. After routing, it should be level from front to back 

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