Log Home Building Course

Let's talk about Timber preservative treatment
Timber is treated according to the hazards to which it will be exposed

Before we launch into treated timber, I would like you to be aware that there are naturally durable timbers available which do not require toxic timber treatment.
A word of advice: I believe that treating non durable timber is essential, you are protecting your investment, it is a fact, borers eat some types of timber, however, we can successfully treat using Borates, which do not present a health hazard to us. We treat timber to give it a longer lifespan. There are effective and non-toxic ways to protect your log home, and give it more value, all of which is covered in detail on the course.
Some timber needs protection from wood boring beetles and rot. This depends on the circumstances, where and how the timber is used, species, location, climate, etc.
My favorite Eucalyptus timber heartwood is naturally beetle resistant, therefore, none of the sawn board timber (floor boards, etc.) in my home requires treatment.

We call this 'hazard class'. Click here for a hazard class chart
Let me very briefly explain:
If the timber is to be used indoors, not in ground contact, it is considered as a low hazard and and would fall into hazard class 1, or H1.
If it is outdoors, in ground contact (fence poles, etc), this is a higher hazard, the treatment is more 'heavy duty' is referred to as hazard class 4, or H4.
The most hectic environment for timber is the ocean, the marine borers are very active, this is considered the highest hazard class - H6.
It is not necessary to treat your log home to H6 - unless of course you are building Noah's ark.
Some timber does not require any treatment, this is discussed in class.

cca treated timber galvanic reaction

Personally, I do not believe in exposing myself or my family to any potentially harmful chemicals. I prefer to take a precautionary approach and I urge you to do the same.
In South Africa, construction timber must be treated according SANS 10005 'The preservative treatment of timber'.

Fastener corrosion issue

The copper which is impregnated into the timber with several of the preservative treatments has a galvanic reaction with galvanized metal fasteners, (screws, nails, brackets, etc), this causes them to corrode rapidly. If your house is built out CCA or ACQ treated timber, you may have a problem in the future when your house falls apart due to failure of the fasteners.

corroded screws
Imagine what happens if your whole house is held together with these things?
How long will it last? A galvanic reaction occurs between the copper in CCA treated timber and the zinc plating on the screw (you have created an approximately 0.8 volt battery). When this occurs, the copper in the timber always wins and the fastener always loses.
Get the full tech here.
Moisture is required and acts as an electrolyte. (readily available on an exposed deck each time it rains) CCA treatment is being phased out in many places and is often replaced by ACQ, it is less toxic but has a severe corrosion problem.

My opinion
Many of these treatments are so toxic that the treated timber should not be sold to the unsuspecting public without warnings and documentation on how one should work with, use and dispose of, in order that we all may make an informed decision, have you ever been told that timber bought in the hardware shop is toxic? How would know? What happens when it is second hand and / or has been cut into pieces and lost it's SABS treatment marking?

What is LD50?

LD50 is a way of indicating the toxicity of a substance, ie. the Lethal Dose which on average will kill 50% of the population, some people will have more tolerance and some less.
"the dose makes the poison." (anything can kill you in large enough quantities).
It is usually quoted in grams per kg body mass (g/kg), ie the bigger you are, the more you can handle.
To put it all in perspective.
Table salt (Sodium chloride) has an LD50 of 3g/kg, an average 100kg person, would require 300g for a lethal dose.
Borax has an LD50 of 2.9g/kg body mass, therefore an average 100kg person, would require 290g, ie. slightly more toxic than table salt.
Arsenic has an LD50 of 8mg/kg body mass, therefore an average 100kg person, would only require the very small amount of 0.8g. (no much)
Bananas have an LD50 of 5.33 bananas/kg body mass, ie. if you weigh 100kg, eating more than 533 bananas at once can cause death.

All treated timber must be marked with a stamp or a tag.
What does this tag tell us?
All I want to do is to be able to make an informed decision
Bill of Rights of our South African Constitution
Section 24: (a)Everyone has the right to an environment that is not harmful to their health or wellbeing.
Here are the treatments approved and required by our Government for treating 'machined poles for log homes'.
To clarify things, building a genuine log home does not involve using 'machined poles', we use 'unmachined poles' however this is the closest specification.
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CCA (Copper, Chrome, Arsenic)
  • Effective timber treatment.
  • This chemical can only be applied in a controlled industrial pressure treatment process, forced into the timber under pressure. The intention is that they get forced right into the timber cells and remains bound or 'fixed', therefore this is not a timber treatment which an individual can apply.
    The treatment solution is acutely and chronically toxic.

    Some methods you can use to ingest:
  • Oral - eat it.
  • Dermal - anything that you touch (floor, deck, handrail, children's playground climbing frame, etc).
  • Inhaled - Burn it and inhale the fumes.
  • What effects can it have?
  • Mutagen.
  • Carcinogen.
  • Reproductive / Developmental.
  • Systemic, possible nervous system damage - Getting nervous yet?
  • Ok, lets take a brief look at the ingredients:

    Copper prevents decay
    Chromium trioxide acts as a binder
    Arsenic pentoxide prevents..... read more.

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    • Effective timber treatment.
    • Not corrosive to metals.
    • Flammable
    • Oily and dark in color.
    • All tar based preservatives are toxic.
    • Contains Benzopyrene - a known carcinogen.
    • Can lead to changes in skin pigmentation
    • Benign skin growths may result in skin cancer
    • Inhalation of vapors may present a lung cancer hazard
    • LD-50 = 750mg/kg
    • 'Aromatic' - a polite way to tell you that it stinks. The smell can permeate food and other materials without them actually coming into contact.
    • Take my word for it - nobody wants this tar all over their beautiful log home.
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    ACQ (Ammonium copper quartenary)
    • Effective timber treatment.
    • Not a DIY product, needs an industrial pressure treatment process
    • Less toxic than CCA, the Arsenic has been removed.
    • The timber often has a green color.
    • ACQ-treated timber is five times more corrosive to common steel.
      Unstoppable galvanic corrosion. ie. The fasteners corrode and your house falls apart.
    • ACQ acts as a surfactant (wetting agent) which lowers the surface tension of water, which helps to absorb moisture, keeping that galvanic reaction going more efficiently.
    • In some countries, ACQ is seen as a replacement for CCA.
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  • Effective timber treatment.
  • Not corrosive to metals.
  • Very effective flame retardant.
  • Environmentally safe
  • Used worldwide for centuries as an economical and environmentally safe timber treatment. No special industrial processes or equipment needed for successful DIY application. Applied to freshly felled wet logs, using the moisture in the timber as a carrier, diffusion draws the borates into the timber.
    This is the only timber treatment that I use, due to the fact that it is:

    • Not corrosive to metal fasteners, due to it being non-metal.
    • Considered environmentally safe.
    • Naturally occurring mineral.
    • Anti-fungal and antibacterial.
    • Toxic to insects but not to mammals.
    • Slightly more toxic than table salt.
    • Ingredients are readily available and cheap.
    • Colorless and odorless.
    • An excellent fire retardant.

    We use a mixture of Borax (sodium tetraborate decahydrate) and Boric Acid.
    Boric Acid is not soluble at room temperature, it crystallizes inside the timber and only becomes water soluble between 60-100 deg Celsius, therefore cannot leach out of the timber at ambient temperatures.

    Note: Not for use in ground contact.