As you may be aware I am building a Geodesic Dome Greenhouse using tanalised timber but this has thrown up a big problem. I am having to mill an angle on all my timber and I am creating a load of toxic sawdust wich I have no idea how to get rid off.
I want to start using a non treated timber and then treat it after all the milling is done.
So I am looking for a permies friendly wood preserver
It is probably too late for this idea, but there is a new-ish type of lumber that most people haven't heard about. Several companies are now thermotreating/cooking inexpensive species of hardwood lumber, and it offers the same physical properties of the original hardwood, with the rot resistance of pressure treated softwoods, without the addition of chemicals. It also gives the wood a darker color, but you do have to put on some type of uv protector to prevent fading. It costs slightly more than pressure treated lumber, but it seems like it would be perfect for this dome application.
The big application right now is for decking and siding, but some people are also making furniture and even outdoor kitchens out of it. It is not commonly available everywhere, but it is started to gain traction in the U.S.
I agree with Bill, that Yakisugi (grilled cedar) 焼き杉 and natural species resistant to rot, plus other traditional methods are going to be the primary focus for natural/traditional builders for the near future, and perhaps beyond. There are some on the horizon with great potential. Something I have been following and researching for about 3 years now is called Acetylated wood.
Of everything I have my "ear on" in the "green" or "environmentally safe" world of R&D for "treated lumber" this one appears to be really the one grabbing attention...and big investors. I have seen several samples and examples of the work and it is quite impressive. Of the 15 or so glass and wood skyscraper slated to start this year, several may have this type of wood, especially for the foundations.
The best preservative is to use no preservative in my opinion, but to use the right timber for the job. Poplar and ash will rot away quickly in contact with the ground. Try using Black locust/ honey locust or sweet chestnut. Oak and chestnut ( the heartwood) will last about 40 years, even in contact with the ground. Our sweet chestnut horsepen has a 40 year warranty to it. These timbers can be harvested by yourself most of the time. I have found sheds made from a tropical hardwood called Bankirai /Bangkirai and it just lasts indefinitely. If you use yakisugi on the previously mentioned non- tropical hardwoods they probably will as well.