How to Flatten a Whetstone for Instantly Sharper Knives

Whether you enjoy creating unique meals at home, or simply need to prepare food for a ravenous family, you should never underestimate the benefit of a sharp knife. Having a sharp knife blade will improve your accuracy and control, while reducing the potential for the blade to slip while you are cutting or slicing.

Whetstones are one of the best tools for sharpening your knife blades, however, without proper maintenance, a whetstone can actually end up causing more harm than good to your blades. The problem is when they start to dish out in the middle To prevent this dishing from affecting blade geometry, you need to regularly flatten the whetstone to ensure you are always sharpening your blades against a flat surface. Use this guide to learn how to flatten a whetstone and find out signs that indicate your whetstone requires flattening.  

Why is Flattening a Whetstone Important?

Flattening a whetstone is part of maintaining your sharpening tools and keeping your knives in top condition. Constantine Delnero, founder and chief blade o fficer at Seido Knives says “don't neglect to flatten your whetstones. They dish out in the middle over time.” When this occurs, the dished stone causes an uneven result on your knives, ruining the blade geometry. 

A flat stone allows you to hold a constant angle, which is essential for a sharp edge. Additionally, the flat surface ensures even contact with the blade, preserving blade geometry and making sharpening faster and more effective. It should also be noted that light flattening removes less material than more severe flattening, which is required if you let the stone get to a point where it has deep dishing. Flattening your stone more regularly will allow you to extend the lifespan of your whetstone. 

How Often Should You Flatten a Whetstone?

The frequency with which you flatten your whetstone often depends on the grit, since coarser-grit whetstones will typically dish out faster than fine-grit whetstones. Coarse-grit whetstones, ranging from about 200 to 600 grit, should be flattened once every one to two sharpening sessions. Medium-grit whetstones, ranging from about 800 to 2,000 grit, should be flattened once every two to four uses. Fine-grit whetstones that are about 3,000 grit or more should be flattened every four to six uses. 

However, even when following this basic frequency pattern, there may be times when you need to flatten the whetstone sooner. Watch out for these signs that it is time to flatten your whetstone: 

• Visual Dishing: The center of the stone looks scooped out, or the edges are rounded.
• The Straight Edge Test: Place a ruler or straight edge across the stone. If you see light passing under it in the middle, the stone is dished.
• Uneven Pencil Lines: Draw a grid on the surface with a pencil. If, after a few strokes on a flattening plate, parts of the grid remain, those are low spots.
• Wobbling Blade: The knife rocks or wobbles when placed on the stone, indicating a non-flat surface.
• Uneven Bevel: The knife edge develops an inconsistent width, with some parts sharpened more than others.
• Slow Progress: The stone feels like it is not cutting effectively, as the worn-out center fails to lift a burr, often leading to a rounded edge.

Related: The Secret to Razor-Sharp Knives Most Home Cooks Skip

How to Flatten a Whetstone

Step 1: Mark the Stone

Use a pencil to draw a grid or series of "X" marks across the entire surface of the dry whetstone. The purpose of this grid is to give you an easy-to-reference visual guide. The marks will remain in the concave dished areas until the stone is flat. Once all the pencil marks have been removed, this indicates that you have successfully flattened the whetstone. 

Step 2: Soak or Wet the Stone

Not every whetstone requires soaking, so be sure to check the type you have before you submerge the stone. For instance, splash-and-go whetstones only need a bit of water to wet them. They do not need to be soaked before you can flatten them. However, if you have a traditional whetstone that does need to be soaked before use, then submerge your whetstone in water for roughly 10 to 15 minutes. If using a ceramic flattening stone, soak it as well until it stops bubbling.

Related: How a Knife’s Steel Type Affects Sharpening

Step 3: Flatten the Whetstone

Ensure you are working on a flat surface, then place the flattening stone or lapping plate on the whetstone, or place the whetstone on the flattening stone, depending on your preference. “To flatten a whetstone, use a dedicated flattening stone (sometimes called a lapping plate) and rub it in a circular, figure-eight, or back-and-forth pattern until the entire surface is even again,” explains Delnero. 

Rub with firm, even pressure, applying water constantly to wash away any slurry that is produced in the process. Stop periodically to inspect the pencil grid. You will notice the marks disappearing from the edges first, as the center is typically the most worn (dished) part.

Step 4: Finish and Rinse

Once all pencil marks have completely vanished, the stone is flat. Rinse both the whetstone and the flattening tool thoroughly under running water. If you plan to use the whetstone immediately, then don’t let it dry out. Simply move directly into sharpening your knives. But if you are only flattening the stone, then give the whetstone and flattening tool time to properly dry before storing them until next use. 

Step 5: Optional: Bevel the Edges

After flattening the whetstone you can use your flattening tool at a 45-degree angle to lightly grind the sharp corners and edges of the whetstone. This prevents the edges from chipping or snagging your knuckles during future sharpening.