Posts tagged “Sandblasting

Sandblasting Some Large Eastern White Cedars

Prior to last week I had only tried sandblasting on one small cedar. The results were excellent, but I was limited to using my friend’s small parts sandblasting cabinet which could only handle a shohin sized tree. Recently, however, a member of our club got a full sized sandblasting tank and offered to let me try it out on some larger trees. Often sandblasting is done in an enclosed tent or room, but we just did it out on his lawn.

This tree was collected in spring 2013. Last year I did a rough initial cleaning on it using hand tools, but with a craggy old thing like this, sandblasting is the most efficient way to clean away all the old dead bark while preserving the details of the deadwood. Many of the cracks and crevices are impossible to access with hand tools. Sandblasting should be a once-in-a-lifetime event for a tree. Once it is done, the deadwood can be maintained over the years with gentle brushing (water and toothbrush) and lime sulfur application (although this is often unnecessary on thuja as their deadwood will naturally bleach in the sun as long as it is clean).

We used aluminum oxide media at 50-90 psi.

The tree before sandblasting. The trunk was wet at this point as it had been raining, so it is much darker looking than it actually is.

The tree before sandblasting. The trunk was wet at this point as it had been raining, so it is much darker looking than it actually is.

Preparation is important. Covering the soil prevents it from getting blown away. Covering the foliage is absolutely necessary. We chose to cover the live vein with modelling clay as insurance, although this is not strictly necessary if you are careful. The bark is surprisingly resistant to sandblasting. I've seen pictures from Takeo Kawabe's book (Kimura's student) who seems to sandblast junipers with no live vein protection.

Preparation is important. Covering the soil prevents it from getting blown away. Covering the foliage is absolutely necessary – it will die if it is hit by the media. We chose to cover the live vein with modelling clay as insurance, although this is not strictly necessary if you are careful -the bark is surprisingly resistant to sandblasting. I’ve seen pictures from Takeo Kawabe’s book (Kimura’s student) who seems to sandblast junipers with no live vein protection.

After about two hours of sandblasting. 90% of that time was waiting for the tank to repressurize. Sandblasting requires a high CFM compressor and the one we were using was unable to keep up for more than a minute or two.

After about two hours of sandblasting. 90% of that time was spent drinking beer and waiting for the tank to re-pressurize. Sandblasting requires a high CFM compressor and the one we were using was unable to keep up for more than a minute or two.

Unwrapped.

Unwrapped.

Very happy with the results.

The medium we used left a slight texture behind on the deadwood but it is all we had to work with. I am still very happy with the results. The live veins will be further defined over the coming years.

This heavy break will unfortunately be hidden in the back of the tree. It is gorgeous but there are always compromises with yamadori.

This heavy break will unfortunately be hidden in the back of the tree. It is gorgeous but there are always compromises with yamadori.

Another candidate for sandblasting. This tree was probably collected in the 80s and was once a bonsai, but  had been growing as a garden plant for 10-15 years. Most of the branches are unusable and it will be a challenge to bring this one back.

Another candidate for sandblasting. This tree was probably collected in the 80s and was once a bonsai, but had been growing as a garden shrub for 10-15 years. Most of the branches are unusable and it will be a challenge to bring this one back. I’ve been rehabilitating it for two years, but you can only expect so much backbudding from a thuja.

After blasting. No trunk protection was used to sandblast this one.

After blasting. No trunk protection was used to sandblast this one.

You can see where some of the bark was blasted away, but nothing too major.

You can see where some of the bark was blasted away, but nothing too major. I will likely polish the bark on this one anyway.

Original front of the tree 20 years ago. Likely the new back as the deadwood is quite flat and the inverse taper more pronounced.

Original front of the tree 20 or so years ago. It is likely to become the new back as the deadwood is quite flat and the inverse taper more pronounced.

An old picture of the tree.

An old picture of the tree from the Toronto Bonsai Society website.

This tree was also sandblasted then a basic structure was set. Sorry, no before picture. It was collected in the 90s by a senior club member and is very overgrown, therefore it will be a few years before it is presentable.

This tree was also sandblasted then a basic structure was set. Sorry, no before picture. It was collected in the 90s by a senior club member and is also quite overgrown, but not as bad as the previous one. It could be presentable in two years.

 


Sandblasting Thuja Deadwood

For years sandblasting has been used in some bonsai circles to clean up deadwood. The idea is that it will remove fuzz from carving, smooth “new” sharp edges created from carving, and strip away old dead bark while preserving the natural texture of the wood.I’ve always wanted to try it on Thuja since they have so many intricate little details which are often covered by old caked on dead bark that is extremely difficult to remove. The alternative is that you pick away at the dead bark with your fingernail or a variety of pointy tools, ideally after rain since the bark is soft. Still, it can be very difficult to get everything and not destroy the little details.

My friend has a sandblaster with a small cabinet so I thought this little guy might be my first test subject.

I've already spent lots of time picking and scraping at the dead bark on this one, but there is still a film of stubborn bark here and there, and the tiny jins on the character spire I am finding impossible to clean without breaking.

I’ve already spent lots of time picking and scraping at the dead bark on this one, but there is still a film of stubborn bark here and there, and the tiny jins on the character spire I am finding impossible to clean without breaking.

Sandblasting works best on junipers or “driftwood species” like Thuja which have a defined live vein that has been cleaned of bark. To prepare the plant for blasting, use a tacky clay like Plasticine to cover the live vein from the soil line to as far up the primary branching you can get. Protect the foliage and pot as best you can. I used aluminum foil and shrink wrap. A cloth and shrink wrap would have worked just as well. This step is MUCH easier if the tree has no wire on it (I learned that the hard way).

The sandblasting was done with a standard glass bead abrasive. I found 70 psi to be pretty ideal.

The sandblasting was done with a standard glass bead abrasive. I found 70 psi to be pretty ideal.

I was very impressed with the results. I kind of expected the small jins to be blasted off, but they were left completely intact and clean as a whistle! Some people might be concerned that the natural silver patina of the deadwood has been lost. Well, if you use lime sulfur that shouldn’t matter to you. Furthermore, I find it takes two years in my yard for this silver colouration to return. In bonsai terms that isn’t really long. Is this a technique I will start using more regularly? While I still need to spend some time closely examining the results, it seems very likely.

After sandblasting.

After sandblasting.

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