flattening live edge slabs

Flattening a live edge slab is a relatively simple process if you have access to the right equipment. We use Wood-Mizer’s SlabMizer slab flattener, which is basically a large router attached to a moving head that glides across the slab and removes fractions of an inch with each pass. After you surface across the entire slab, you simply lower the head of the router to do the next pass. Once the entire slab is flat, you’re good to do the other side.

In the video below, we show what a few passes looks like on our Wood-Mizer SlabMizer slab flattener.

Why Flattening Your Slabs Is A Must

Flattening should always be done when working with live edge slabs. Since slabs typically take 2-3 years to properly dry, they can warp with time as they dry at different rates on different parts of the wood.

Slabs are commonly used for dining tables and other furniture and nobody wants a table that isn’t level. Flattening ensures the entire slab is the same width throughout and that it will sit flat on a base. If a large slab is twisted even as little as 1 inch, it will be tough to mount to a base.

Another reason flattening is essential is because slabs are typically rough cut using a chainsaw mill. Flattening the slab will remove the rough chainsaw marks and reveal the grain pattern of your slab. Live edge slabs are expensive, but without flattening to reveal their beauty, they just look like a dirty piece of wood. Don’t take my word for it, check out the images below of a walnut slab before, during, and after flattening.

How Much Do You Lose On Thickness From Flattening?

This is one of the trickiest questions we get from customers, as it varies with each and every slab based on how warped the slab is. If the slab is already relatively flat, a few passes on our flattener usually does the trick. This results in 1/4″ or less being removed from the thickness. With large slabs, 1/4″ being removed is usually about the minimum you’ll see. On large slabs that are more warped, we’ve had to remove more than 1″ at times to get the slabs flat.

Generally speaking, when cutting your slabs, you’ll want to go at least half inch to one inch thicker than what you want your finished slab to be. Then you won’t remove from the thickness you need when you flatten your piece.

Getting The Maximum Thickness From Your Slabs

It’s worth noting that when you flatten a live edge slab, the opposite corners are typically the high and low spots. For example, the back right and front left could be the high spots on the slab, and the back left and front right could be the low spots. The larger of the slab you’re working with, the more you’ll have to remove to get to the low spots. For slabs with a lot of warping, it often makes sense to cut them to size before flattening, or down the middle. The less surface area you have to flatten means the thicker your slab will be once it’s completely flat.

Another trick you can do is use shims on the low spots of a slab (which are typically opposite corners) to remove less on the first side you flatten. Do not use shims on the second side, or your slab won’t be flat. However, using them on the first side puts your slab as level as possible, resulting in less waste.

What If I Don’t Have a Flattener?

If you don’t have a slab flattener, your best bet is to ask your slab supplier. Most businesses that sell live edge slabs will have a flattener in their woodshop. We offer flattening services for $80/hr. Although this results typically in $80-$160 of additional spend on each large slab, it saves our customers time and money from the other option.

The other option is building a flattener by making a sled and using a router. This option isn’t usually ideal, as you’ll have hours of labor wrapped up in this alone. You’ll also spend a few hundred dollars to build the sled, especially if you don’t already own the router. If this is a route you’d like to consider, feel free to do a Google search to get more information. This isn’t a method I’ve ever used, so I cannot speak for it’s effectiveness outside of what I’ve seen online.

Questions About Flattening?

If you have any questions about flattening, I’m happy to help. Simply drop your questions in the comment box at the bottom of the page. If you would like to inquire about buying live edge slabs that are already flattened, simply contact us online.

10 Comments

  1. Mike Domenica on March 4, 2024 at 6:16 am

    I have a 5 foot long17 inch wide, warped 3.5 inch thick live edge slab on which I need to put iron legs to use as an out door rustic bench. The warp is about 1 inch inch across the board or about 1/2 in at the center. I don’t have access to a flattening machine. Can I hand chisel out flat surfaces to make a flat base for the table legs? Any suggestions?

    • LLE Support on April 23, 2024 at 9:10 pm

      You could, but the top is still likely warped in that scenario. You can make a flattener out of a router if you have one, or there are cheapear products on amazon! They just take a bit more work to flatten a slab.

  2. Laurence on July 27, 2022 at 2:18 pm

    Hi Peter
    What side of the slab is best to start to flatten on . My slab is slightly bowed at corners meaning I have a high spot on the other side .
    Thanks

    • Lancaster Live Edge on September 6, 2022 at 6:08 pm

      Either side works. If it’s badly warped, you can put shims under it on the first side to level it as much as possible. Then flatten the majority, flip it and flatten the back, then flip it to get the rest on the first side.

      This is the best bet to minimalize the loss of the wood’s thickness.

  3. Ben Trem on March 12, 2022 at 6:26 pm

    After flattening both sides of a slab, do you typically lay it flat & put weight on it, or lean it upright against a wall?

    Also- how long after flattening do you wait until pouring epoxy?

    Thanks a million!
    Ben

    • Lancaster Live Edge on March 22, 2022 at 7:29 pm

      Weight won’t help too much at keeping it flat. Standing it up against a wall is ideal, but if the wood isn’t properly dried for the environment it’ll be used in, it’s going to warp or crack in most scenarios!

  4. Peter von Schondorf on August 21, 2021 at 1:00 pm

    I have a large slab, approximately 6 ft. by 3.5 ft. (widest dimension) with a large area with pits and holes. The slab is about 4 inches thick. Many of these holes and pits are interconnected, and as a result it will take a large amount of epoxy to fill them. My guess is 4-gallons. One big problem area is where one of the pits form an edge. Wondering if you have a technique for daming this type of live edge -thanks

    • Lancaster Live Edge on December 28, 2021 at 4:45 pm

      Hi Peter,

      For this – we typically build a mold around the slab, then put caulk around the problem area to completely seal it off. Caulk, tyvec tape, and 1/4″ HDPE plastic sheets can do wonders!

  5. Jackson on January 6, 2021 at 7:07 am

    How long would it take to flatten a slab that’s 16″ x 60″?

    • Nolan Barger on January 6, 2021 at 7:16 am

      Less than an hour. Typically to flatten both sides it would take about 30-40 minutes, but that would vary based on how flat the slab is to begin with.

Leave a Comment