Wednesday, December 7, 2016

Project #14 - Mounting Aiiwatani natural stone on a wooden board

This is another project not directly related to knifemaking. Friend of mine asked me whether I could help him to mount his new Aiiwatani sharpening stone from JNS on a wooden board. I


  • Plum wood (flat and dry), cca 3cm thick
  • Shellack (flakes)
  • 95+% acohol
  • hair brush
  • Epoxy (G/flex)
  • 5 minute epoxy
  • Diamond flattening plate from JKI
  • brass (metal) brush
  • sanding paper (120, 240, 400, 1000)
  • steel wool (extra fine)
  • marble table top plate (used as flat surface to support the sanding paper)

 have not done that before and at the beginning got a real headache researching what materials to use to seal the stone and to finish the surface of the wood. Cashew lacquer is often recommended to seal sharpening stones, but I could not get my hands on any, then there is Urushi which is rather expensive plus different modern water resistant . For wood there are many different options. Finally - I have decided to go with shellack and it turned out to be a good solution.

So - I started finding a nice flat piece of plum wood. Why plum wood? It was not too expensive, it is a hard wood and it holds up well with water around (I have 2 plum wood spoons and they are great) and it looked lovely. And it had the proper width, so I did not have to do much cutting :)

I started with cutting the board to size. I was left with a piece of about 8 x 10 cm large and I have decided to use it to test the finish.

The wood - testing

I have first rounded all corners with a file and then sanded the wood with 120, 240, 400 and 1000 grit sanding paper. With the bottom I only went up to 240 so it would not be sliding on wet surface too easily.

Left: original surface of the wood
Right: Wooded sanded to #1000 and finished with steel wool

I have mixed the shellack with alcohol at a ration 1:5 (weight). I actually first did 1:3, but that has proved to be too thick. 1:5 ratio made it easier to get an even layer on the wood.

When I was lacquering the testing piece I sanded the wood with steel wool after each coat. That has proved not to be the best idea as the coat was so thin, than I nearly completely took it of. After this experience I first did 3 thin coats on the board before I would sand it with a steel wool. I would then apply 4th coat and sand it again (very lightly). Because I have used steel wool to finish the surface it was not polished, but slightly matted (but still very smooth to touch).

The stone - testing

To test the second step I have used small piece of stone that was a by product of making fingerstones. I have flatten it with the diamond plate before put tin on a few coats of shellack then glued it to the testing board using epoxy. Since the bond was very strong I have proceeded to the main board & stone.

Piece of stone glued to the testing board using epoxy.

Preparing the stone

This was a little challenging. The stone did not have a regular shape and the bottom of it was strongly uneven. While it was not necessary (and frankly also not possible) to flatten the whole bottom side of the stone, I wanted to achieve to have contact points over full length and width at least on some areas of the stone. Even though this stone was not particularly hard, I needed 2 hours of work to get the result I wanted. During this process a short-hair metal brush proved very helpful to remove stone dust from the diamond plate. When finishing the stone shaping I was particularly careful to make sure the flattened part is indeed flat.

After about 20 minutes of flattening with the diamond plate.

After 2 hours of flattening.

A lot of stone dust was produced in the process
Once the stone was flattened I have brushed the whole bottom side and the sides with the brass brush to remove all the dust and loose little pieces of stone. Subsequently I have covered the whole top (sharpening) surface with an orange Tesa plastering tape (this is my favourite for these purposes as it does not leave any residue) and started to apply coats of shellack. Over the course of a few days I have applied around 8 coats. This created smooth glossy surface on the stone.

The stone was very thin in one place. To minimize the risk of loosing this part too early I have applied a thick layer of 5 minute epoxy from underneath to support the thin stone. This worked rather well.

Applying a layer of epoxy to support thin part of the stone.

 Preparing the board

I have basically followed the steps as described in the testing. To speed up the sanding I have taped a sheet of sanding paper to a marble plate which gave me a perfectly flat surface to sand on.

Sanding the wood.

Once the wood was sanded I have applied 3 coats of shellack, then gently polished/sanded it with steel wool. One more coat and one more sanding and it was finished. The shellack really brought up the fine structure of the wood. I could not help but think that it would have made for a few lovely knife handles :)

Applying a coat of shellack to one side of the stone. 

Detailed of the finished surface


This may sound trivial, but it proved a little tricky. One of the less ideal decisions was to chose a thin and long curing epoxy (G/flex). I really like this epoxy and have made very good experience with it so far, but being really on the thin side made the gluing a lesson in patience. The slow curing was the good part of it, as it actually takes quite a while to mix and apply this large amount of glue (and I had to mix up some more as I underestimated how much will be necessary), but being thin the glue had a tendency to run off long after I have expected it to. 

Using a clamp and machinist square as an 'anchor' to keep the stone in place
while the glue was curing.
Finished stone.


Arguably this was a relatively simple project and since I (apparently) did not make any major mistake it turned out really nice. One possible update to the future would be to grind/sand the wood from the bottom part so that board would get a slightly 'bridge' like shape standing only on the ends of the board. All stones that were mounted in Japan were done this way - I suppose to allow the wood to dry after sharpening.

Also, since this project went rather well I will son be mounting a lovely Aka-Renge shiro suita from Ohira-yama in a similar manner.

Thank you for reading, please do not hesitate to ask questions :)

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