Methods of Wood Preservation

Wood does not decay naturally through age nor will it decay if it is kept constantly dry or continuously submerged in water.

The Common Cause of Decay in Wood are:

1. Alternate moisture and dryness
2. Fungi and molds
3. Insects and worms
4. Heat and Confined air

The essential requirements to achieve successful preservation of wood is through good seasoning and correct processes of preserving wood enumerated as follows.

I. External Processing is accomplished y coating the wood with preservative chemicals that will penetrate into the fibers.

II. Internal Processing. A chemical compound is impregnated at a specified pressure to permeate the wood thoroughly.  The procedures are as follows. 

1. By impregnating a 2% zinc chloride solution followed by an injection of about 45kg. of creosote oil per cubic meter of wood.
2. The cylindrical tank is filled with creosote oil at a temperature of 93 degrees and the pressure is applied until the wood absorbed the oil to a predetermined amount.
3. A partially seasoned timber us run into the metal cylinder 2.50 to 3.00 meters diameter by 20 meters long with doors or heads bolted. A pressure of 1.5 kg. per sq.cm steam is applied for 30 minutes and maintained from 1 to 5 hours.
4. A vacuum of 60 cm. is  created and maintained for 1-1/2 hours when creosote oil is introduced at a temperature of about 70 degrees Celsius.
5. A pressure of about 12 to 14 kg. per sq.cm is then applied until the timber has absorbed 50 kg. of oil per cubic meter.
6. Another method is by immersing timber into two solutions of corrosive sublimate. One part of bio-chloride mercury to 99 parts of water for a period of 5 to 10 days sufficient enough to ensure through penetration by the preservative. The sublimate is insoluble in water and remains in timber for a longer time than salts like zinc chloride.

   The External non-pressure process of preserving wood is the application of penetrating tar oils, carbolineum, spiritine, solignum, etc. It is applied on the surface of wood either by brush, spray or by immersion.

       External Preservative is effective if the wood to be treated is absolutely dry and well seasoned to absorb a sufficient quantity if the chemicals. All tar oil products should be applied hot.

source:  

Simplified Methods on Building Construction

Max B. Fajardo Jr.