Borates for Protecting Oak Beams

      Borate treatments can provide good protection against insects for softwood that is kept dry, but has limited usefulness on hardwood, especially if exposed to rain. January 14, 2008


We have 1100 bf of oak beams that are stickered and stacked. Would borax sprinkled on and about the stack prevent bug infestation? We are air drying the material, so they will be sitting for a couple years or more.

Forum Responses
(Sawing and Drying Forum)
From Professor Gene Wengert, forum technical advisor:
Exposed to rain? If so, the borax will run out with the rain water. Incidentally, the borax will not penetrate deeply, so you are protecting a layer several 1/100" deep. When you get a check, split or crack, it will expose untreated wood.

From contributor D:
You need DOT, disodium octaborate tetrahydrate (sp?) to get the borate people are talking about. Borax and boric acid boiled together at the right mix for the right amount of time will make that. Dipping (preferably) or spraying the wood, then drying under tin would be sufficient protection. Googling dip diffusion might bring up some hits.

Borates do not run out. They do not leach out of a cell unless the wood is rewetted and the cell goes above the fiber saturation point, that's more than just a casual rewetting.

Nisus Corp. does have a chemical dye that can show penetration depth. I've seen some experiments that show borate penetration clear through 2x stock. You will likely get more accurate information from Nisus or one of the suppliers like Schroeders.

From Professor Gene Wengert, forum technical advisor:
Borax will penetrate into red oak slightly, but not into white oak. Further, DOT will not diffuse into white oak a significant amount and only slightly into red oak if the wood is submerged or constantly wetted with the solution. The issue is that when drying oak beams, you will get checks that are deeper than the solution has penetrated. It certainly will penetrate 2" into pine (that is 1" from each face and pine is very permeable), but we are talking about oak beams here. Further, such penetration results when the wood is soaked in the borate solution and not when it is sprayed on the surface.

Incidentally, disodium octaborate tetrahydrate is commonly sold as Timbor. It is excellent for safely treating wood that is kept fairly dry but is at risk from the Formosian termite (a big problem is some countries and tropical locations), as well as other insects such as the old house borer and the powderpost beetle, both found in fairly dry wood. In my searches, I was unable to find one reference to using DOT or Timbor as an insect preventative or insecticide when drying lumber.

Again, it is worth noting that DOT is highly soluble, so if the lumber is rained on, DOT will leach out and the rain will wash away the chemical, especially the chemical at or near the surface (which will be the situation with oak beams). Without adequate surface protection from DOT, we can expect insect damage and fungal damage in the unprotected surface.

From contributor D:
What would you recommend for large timbers air drying under shelter for a period of several years?

From Professor Gene Wengert, forum technical advisor:
If you check out a book such as "Air Drying of Lumber" by the US Forest Service, the insect risk is not large, so insects are rarely considered when drying. Keeping the yard free of wood debris will eliminate breeding spots so that your lumber will not be located close to any insects. Use dry kiln stickers.

From contributor J:
Okay, sounds good. The timbers are out of the weather, under cover, and have 1" stickers. Good ventilation on the sides, and end-sealed. We will be ready to use the beams in about two years. During that wait, I don't want any bugs to damage or infect the timbers. Timbor sounds good, but I'm thinking that even spraying a pesticide around the pile would be okay, just to keep the pests from taking up residence. Yes, I understand about the sawdust, etc., and pesticide residue, but some of the pesticides available don't last that long.

From Professor Gene Wengert, forum technical advisor:
Pesticides do not work, as the insects are not living in the soil for very long and are not eating the soil, so they do not ingest the insecticide. The insecticide only works if the insects happen to be in the spot you treat at the time you treat it. Spend your time and money keeping wood debris away from the oak timbers and then there will be no source of infection. Note that spraying the wood itself also does no good, as the insects are deeper than the depth that the insecticide penetrates. Also, use stickers that have been in the kiln and have not been left outside (to assure that the stickers are clean).

From contributor D:
I hear what you're saying and don't totally disagree about good sanitation, but I've yet to work on an older house that's framed in oak that wasn't pretty well powderposted. You can reapply borates when the frame is dried in.

From Professor Gene Wengert, forum technical advisor:
I am not against using Timbor, but do not count on it in a drying operation to provide extensive protection. Sanitation is number one. Powderpost beetles do not come until the wood reaches around 30% MC (the outside fibers). However, keep your oak away from any lumber or wood that might have PPB and you should be pretty well protected. Timbor is added protection, which might not be worth the money, but it is okay to use.

From contributor R:
There is a product called ShellGaurd sold by Permachink that is a liquid containing Borax. It is designed for protecting log homes against insects. It is expensive but would protect your beams while they are drying and will continue to protect them after they are used in a building. One treatment lasts forever if the wood is sealed and it is carried into the wood by moisture, so would work well if applied before the wood is dried.

From contributor D:
Check the MSDS - I think it is DOT and PEG.

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