I make my own wood preservative. I could run out and purchase a similar preservative for about $95 a gallon or I can spend about $10 and make my own. I make a simple mixture that I can use in a garden sprayer on my logs.
My ingredients for a home-brew exterior wood preservative include are simply two things: a borate-based product such as Timbor or Penetreat and Propylene Glycol (environmentally friendlier, marine and RV anti-freeze).
People have asked “Why Penetreat or Timbor when for just a couple of bucks they could use 20 Mule Team Borax (Thats right, the laundry and general cleaner). After all it has borates in it and isnt that the same stuff?” No.
There is no doubt that 20 Mule Team Borax is a wonderful cleaner and I use it here at the lodge for many things however it is not the same stuff. Borax is sodium tetraborate decahydrate, a natrually occuring mineral, an inorganic salt. Boric acid is the result of borax reacting with a mineral acid such as hydrochloric acid. The resulting boric acid, trihydroxidoboron, is a great antiseptic, insecticide and flame retardant.
Boric acid kills wood destroying insects and also prevents and destroys existing wet and dry rot in timbers but is the more refined crystalline material used as an antiseptic and is not readily available in useful quantities for wood preservation however, borate-based products are.
Borate-based products such as Timbor or Penetreat both containing the borate Disodium Octaborate Tetrahydrate are excellent and easily obtained.
Both products can be applied dry or dissolved in water in order to make a paintable or sprayable solution of a desired concentration. The solution is best used on bare wood. For interior surfaces I make a 10% solution by mixing one (1) pound of the borate for each gallon of water. For exterior surfaces I will use the same mixture but for certain exterior areas I take an extra step.
On the exterior when I need to treat log ends or wood is subjected to more extreme conditions I make the solution above but instead of using water I use propylene glycol.
Why propylene glycol?
Propylene glycol although does kill existing mold and mildew as well as many wood boring insects, whats more significant is that it is hygroscopic. this means that when sprayed on a log end or exposed grain it follows and attracts the water or moisture from deep in the wood. The water is somewhat ‘replaced’ by the propylene glycol. When mixed with the borate to a 10% solution this becomes a very effective heavy duty preservative.
When the two are used together the borate dissolved in the propylene glycol is pulled deeper into the wood especially when applied to the log ends. As the propylene glycol dries the borate powder crystals will reform.
Propylene glycol is also easy to get. Propylene glycol is the base for earth-friendly antifreeze. I go to the local auto parts store and get a gallon of environmentally friendly antifreeze. If you are planning on making your own then CAUTION: READ THE LABELS! DO NOT under any circumstances use antifreeze with a base of, or containing any amount of ETHYLENE GLYCOL. This is nasty stuff folks DO NOT use. Ethylene glycol can be fatal and must be avoided for this application.
If you are thinking of making this preservative then take every precaution necessary. This post is not meant as a “go out and do it” only as an explanation of what I do. As in the handling on any type of preservative or insecticide YOU are the one ultimately responsible for your actions.
With that said – Now, how do I find propylene glycol based antifreeze? I read the label. I ask for RV and Marine antifreeze then read the label again to confirm that it is propylene glycol and NOT ethylene glycol. Propylene glycol based antifreeze is generally used as an additive to potable water systems in addition to being an engine coolant.
Making the propylene glycol and borate wood preservative is easy.
Similar to the 10% borate-water solution but this time instead of water I pour one gallon of propylene glycol into a five gallon pail. Next I very carefully and gradually add 1 pound of the borate-based powder. Stir slowly adding a little at a time making sure to dissolve the borate powder. Now the mixture is ready to be used.
To make a 15% mixture add 1.5 pounds of borate to each gallon.
I used this propylene glycol and borate preservative mostly to treat log ends where the natural capillary action of the wood can also wick in water. I will also use the mixture on select out of reach areas where I know environmental exposure is greatest. I liberally paint or spray the log ends with the preservative a little at a time to make sure that it soaks in. I have also treated checks (cracks) that may apprear on the upper part of a log before sealing.
I do not go spraying this on broadly across my logs and on all exterior wood — I only use it sparingly and for very specific and select spots.
I never use the propylene glycol and borate preservative on the interior anywhere nor do I use it in areas in close proximity to or probable contact with anyone.
There is a method to create a concentrate by heating the propylene glycol to reduce the water content and then disolving the borate to make the solution. I have done this – but for very specific and limited projects.
If heating the propylene glycol to reduce it – this should be done outdoors only and with the proper safety gear such as long sleeves, gloves and eye protection.
Before applying the preservative to the wood I take the basic steps to make sure that the wood is clean of dirt and debris.
Feel free to leave a comment or a recipe that you have successfully used.
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Is this a mixture you would suggest for treating wood to be used in raised garden beds? It sounds a bit toxic for the soil and plants. I am trying to find a good sealer recipe that will protect my boards from rotting, but not leach any chemicals into the soil. Any suggestions? Thanks!
Hello Sable – I would be reluctant to use this mix for your application as I too would be concerned with the potential for any leaching into the soil in a raised garden. I would be more inclined to use different method.
Creating a raised bed a few years ago for someone I had coated the inside of the boards, before filling with soil, with a roofing sealant. It was a roofing tar that I used. now although that too could leach into the soil I had to make sure that I prevented contact with the soil so I then adhered to tar on the inside a plastic sheeting barrier using a strong plastic drop cloth that I cut to fit. My planter was about two and a half feet high. So from the plastic drop cloth I cut a panel that was 2.5′ wide and then pressed in into place along the entire inside. This would prevent contact with the soil. I did not place any plastic on the bottom of the planter as that would inhibit drainage. Then, using 1″ thick insulating foam board cut and trimmed so that it was about 1″ below the top of the bed (same with the plastic and roofing tar) this way the mulch would hide it from view.
The 1″ foam panels also provided a little bit of additional insulation during the winter for the raised bed and I found that in the summer it also help to keep the soil warm which seemed to encourage root growth.
When adding the soil to the bed I brought the level of the soil up to the same level as the insulating board. Once planted, mulch was added to bringing the level of the bed up to meet the wood sides. this gave me 2″ or so of mulch to help keep my soil moist and soft and hid the tar, plastic and foam board from view.
The tar protected the boards from moisture, the plastic also helped to prevent the boards from moisture but also protected the soil from potential leaching of the tar into the bed or into the ground. Had I not used the tar and only used the plastic I still stood a chance of moisture building up between the wood and plastic. So my method provided water proofing, a protective barrier to prevent leaching into either the bed or the ground as well as insulation for the planter.
The exterior of the planter was simply sprayed and brushed down with linseed oil.
The planters were built a little over six years ago and the original boards are still intact and there has been no sign of rot.
I hope that this helps
Can I use this mixture in my attic and still go up there?
Hello Steve – Thanks for visiting the site. I’m not sure why you would want to use the mixture in your attic. If you have a situation with insects certainly a very light dusting of the dry borate near the eaves would do no harm however the mixture presented here if for out door use only. Propylene glycol is not something I would want applied anywhere inside my home. Please use the mixture only on the exterior and then I only recommend it to be used as a spot treatment where there is an end grain saturation situation – such as at the end of a log that is has been exposed to excessive moisture or as a preventative measure where log, beam, or wood ends are exposed to the elements.
Please do not use this in your attic
I am building a 32′ wooden sailboat using Alaskan yellow cedar, white oak and douglas fir. This boat will be sailed in saltwater. I have completed the hull and am looking for a preservative that I could apply to the unfinished interior and exterior wood. All of the surfaced will be coated with marine paints. Any thoughts about using your boric acid/propylene glycol mix?
Charles — ahh what a wonderful project. I would be hesitant to use this mixture on your sailboat. For your project I would hold off on using this particular recipe as I do not like to use this recipe in close proximity to and frequent contact with any person or animal even though you are planning to encapsulate it with a marine paint.
For your application you may want to take a look at some of the articles presented by Michael Dutton such as “Finish Treatment of Timber Using Natural Preservative: Michael Dutton” or his other article “Make Your Own Wood Preservative With Colorant For A Durable Finish” I believe that those would be much more suited to the task at hand and more serve you better for your application. In addition with Michael’s recipes I would also feel comfortable knowing that they are using natural materials for one and also used to protect outdoor furniture. Give them both a look.
Thanks so much for this recipe, wonderful to be able to use something for termites that does not cost a fortune. I do have a question. After using this spray what should occur? What I mean is, should you see dead termites or other wood eating bugs or does it kill them in the wood. I was wondering if they will come out and look for another food supply? I want to make sure we use it correctly and that it does kill the termites.
Thanks
Hello Judy- You are welcome — If you are seeking to deal with termites this can be of help if you apply to the affected area however, I would be inclined to pass on the glycol borate mix if Im using it indoors. If you are using indoors then I would use the borate at a 10% to 15 % solution dissolved in just water. Spraying the affected area the water should soak in and as it dries the borate will crystallize and will help to an extent. Using a dry borate and dusting the area would, I believe be very effective. Also lightly sprinkle the borate around the inner foundation. Insects crawling through the borate would be doomed as it sucks the moisture out of them. – Ants and termites can carry the dry borate back to their nests and poison the rest of them as well. Borate is a common ingredient in most cockroach, termite, and ant insecticides.
I hope that this helps.
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