Flatting and finishing walnut slabs

Walnut Slabs: flatting and finishing and dealing with waxed areas.


When I receive a log, I cut the end square and wax the ends of the log. This prevents drying of the end grain, preventing checks or cracks, which no one wants.

When I mill wide slabs, I also wax the ends ( last foot of the slab face ) and in crotch areas. This slows down the drying and keeps the checking and splitting to a minimum. Sometimes I wax the complete slab on both sides because there is so much figure with a lot of cross grain. in these cases uneven drying tends to cause cracks.

When walnut is first milled it has a greenish brown hue which darkens when exposed to air and light.
See pic of fresh cut walnut:



If fresh milled slabs are left inside it takes a long time to turn the heartwood dark brown. If you place them out in the sun the slab darkens in a few hours along with the sap wood, just like an apple turns brown.

The longer a log sits before it is milled the more it will oxidize at the ends of the log. This can darken the wood at the end of the log a foot or more and stain the sap wood as dark as the heartwood. A tree which has a small chunk of bark knocked off or damaged, can also stain the sap dark in that area. This happens because air is in contact with the sapwood, which oxidizes it, and it can also stain the wood because all kinds of fungus get in the wood and stain it, just like fungus turns different woods all kinds of colors. See pic


Sticker marks can also be caused by a fungus, which can spread deep into the wood. Stickers are  the wood spacers placed between the layers of slabs to allow air to circulate so the wood can dry evenly.  These marks can be a light stain or a dark stain. Sapwood is the worst part of a walnut slab to keep from staining because that’s where most of the water is in a tree. Mold and fungus need moisture to grow. Freshly milled walnut slabs can get sticker stain in a few hours if stacked with wood stickers right away. I don’t let anything touch the top surface of table top slabs until it has had a few weeks to dry.


I’ve also started coating all walnut slabs with Pentacryl. I started using it to coat large walnut slabs 10 years ago. I've had great success with it keeping slabs from checking and cracking. It also speeds up drying by replacing water. This helps avoid the staining at the sticker locations.

You can read about Pentacryl here:




Bleaching walnut sap wood white:


I have done some bleaching of sapwood and it is a great way to blend light and dark marks out of the sap wood so it looks like it does when it is first cut, before it oxidizes.

A few years ago I started concentrating on how to prevent any sticker marks in walnut sapwood. It's a two week process coating and handling the slabs before they are stickered into a pile to dry. I don't want anything touching the top surface of a table top slab for two weeks and they are kept in an area below 50% humidity for that two weeks.

I also make and use strong oak stickers that are 1 3/4" thick with an air grove down the center. Normal stickers are 3/4" thick and bend easy. Thicker stickers keep slabs flatter and the air grove keeps a narrower part of the sticker against the wood. The wood has better air circulation to prevent mold and fungus growth in the contact areas at sticker locations.

You can see some pics on my facebook page along with a video showing how I bleach the sap wood.
Link to Facebook artical.



Removing the wax on the surface and ends:

When you receive a walnut slab and start to flatten it, don’t try to sand off the waxed areas as it will gum up your sand paper and smear it around. Remove the wax using a hand plane, scraper or run the slab across a jointer or planer. Don't use mineral spirits as it will get in the pores and keep bubbling out for awhile and ruin the finish. Use lacquer thinner or denatured alcohol to remove the wax residue after scrapping.

Note that the waxed areas sealed the wood so it did not oxidize as much as the rest of the slab. That means it will be lighter in color than the rest of the slab where no wax was applied. Slabs sit for 2-3 years and are shed dried and then put in the kiln. They also can sit for a few years after until they are sold and turned into a table top.

When your flattening a slab, the more material you remove, the lighter the un-waxed areas of the slab will get. This is because you are removing the oxidized surface which will match the less oxidized lighter area where the slab was waxed.

If you remove 1/16” to 1/8” to level a slab, you may notice a shade difference between the areas. You do not have to keep removing material to even them out. A couple of customers have done this not knowing what caused the color difference. If you remove more than 1/8" flattening the slab, the color will probably match and you won't see any shade differences.

To darken the lighter areas, put the slabs in a bright area, or sunlight so the lighter area (ends usually) oxidize and catch up to the rest of the slab. This may take a few weeks or more. Test by wetting the area which will highlight the difference. Using a wet rag will work and won’t hurt the slab as the water dries fast off the surface. You can use naptha if you don't want to raise the grain.

Finishing (coating with poly or varnish) the slab early will slow the oxidizing process down because of the UV protection some finishes have.

In the past when I didn’t wax the ends (face) of the slabs a big percentage cracked down the middle, or in crotch area. I still coat the last foot of each slab even though I am coating with Pentacryl.

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