Architecture

WOOD TREATMENT DOT METHOD

Nov 30, 2017 |

A Pilot Project to Enhance the Material that to be used in Reconstruction Architecture San Frontiers – Nepal.

ABSTRACT

ASF-Nepal carried out the pilot project on the “Wood Treatment” to enhance the use of the wood as a sole product to be used in the “Build Back Better” reconstruction project. As a part of project, especially in rural areas, use of logs / timbers / woods has been prioritized by different organization and agencies. Use of seismic band has been made mandatory in most of building cost issued as a part of re-construction. Use of timbers as seismic band is the tradition practice which has been promoted by latest norms and standards. To make sure that the timbers used in such a crucial elements is long lasting and is not affected by termites, DOT wood treatment has been the most economical method.

INTRODUCTION

After the devastating earthquake on April 2015 & May 2015, Nepal has been progressing in a positive direction as much of the Government and Nongovernment Agencies are focused on the Re-constructional projects.

Reinforced Cement Concrete Buildings are restricted to the urban area of the country due to economy, accessibility, practicality etc. Still in the rural area, we can see the use of traditional vernacular architectural buildings which seems more comfortable as per the use, climatic condition, geographical feature etc. It has been understood that if designed and constructed properly, these traditional materials could be used to construct an earthquake resistant building. Not just technically, socially as well, it is better to use these traditional materials to construct a new earthquake resistant building in future.

Timber is one of the traditional material which is found in ample amount in rural area. ASF- Nepal is working on the pilot project to treat the timbers environment friendly way so that these could be used as one of the crucial materials in building construction in rural areas.

Wood in its natural state has been a reliable construction material since the beginning of civilization. However, because wood is a natural, organic material, it is at risk of bio deterioration in certain circumstances – for example, in wet conditions or in area with a high termite hazard. Wood can be protected from attack by pests with preservative treatment. Environmentally – DOT is an appropriate choice to protect wood from destroying carpenter ants, beetles, termites and decay fungi.

USE OF TIMBER

Traditionally and culturally, timber has been used in our life-style from the shelter home to funeral fuel. So we can ignore the use of the timber in our lifestyle as well as building construction though the use of timber has been restricted due to various reasons such as environmental affects, un-practical etc. With development and modernization, use of timber at present scenario has been limited to only in rural areas. Timber as a fuel has been controlled by different Governmental and Environmental Agencies however timber as a building construction is still effective in rural areas.

There are various parts in the building where timber can be used and even more effectively. Generalized areas where timbers are most commonly used in the rural area are as follows:
1. Timber Post (vertical Columns – especially in the porch area)
2. Timber joint / panels for the floors for the diaphragm
3. Timber Truss and purlins for the roof
4. Timber Staircase
5. Timber Doors & Windows
6. Horizontal Sill & Lintel Bands
7. Seismic Timber joints at corners

IMPORTANCE OF TIMBER TREATMENT:

Architectural San Frontiers – Nepal, is also a pioneer organization working in reconstruction program. Better than working in the similar field as other organization, ASF-Nepal chose a unique topic “Timber Treatment” so as to focus on the use of accessible product in the rural area.

It is well known fact that termites, ants, bugs and decaying fungi are the major threat for the timber. These insects feed on the timber and destroy the age of the timber ultimately destroying the building. Good building materials are the backbone of earthquake resistant structure so the timber that we recommend to be used in the Re-construction need to be free from infect as far as applicable.

DOT treated wood can be used for all interior works which are placed above ground and out of contact with liquid water. When used in weather protect exterior environment, treated wood must be continuously and properly protected with a minimum of one coat of primer and two coats of exterior paint.

Cultural Treatment :

As mentioned above as well, fuel wood is the main source of cooking in the rural part of the country. In addition, cooking with the smoke has been our tradition as well as culture. Fortunately, smoke has been one of the traditional and cultural treatment technologies which we have ignored as we moved on to urbanization.

The wood used inside are mostly treated with smoke which keeps the termites, bugs, ants and decayingfungi away from the wood ultimately increasing the age of the wood. Previously, Chromated Copper Arsenate (CCA) was the most accepted and popular form of treatment procedure throughout the world. After ban of few substances within the chemical, Chromated Copper Boron (CCB) was brought to practice through which DOT treatment technology was derived.

DOT:

Unlike other wood preservatives, sodium borates remain water soluble. This means the chemical is mobile in the wood and can diffuse throughout the wood if enough water is present. For this reason, DOT treatment typically provides a deeper shell of protection than other preservatives.

DOT treatment is as effective as wood preservative. Although low in toxicity to mammals, DOTs are toxic to decay fungi and a broad spectrum of wood destroying insects, including carpenter ants, wood boring beetles etc. The mode of action is not fully understood, but borates appear to disrupt the digestive process of the insect, causing it to starve.

LIMITATION:

Though various experiments are being carried out successfully, there are few limitation on DOT treatment which need to be listed prior to use:
a. It is better to have pressurized treatment which is generally used in Europe.
b. The treatment does not kill “carpenter ant” which do not feed on timber.
c. The ratio of the chemicals in the solution is not stabilized. It depends on the type of wood and harvesting time period.
d. It is not recommended to be used in exterior wood as the chemically could be easily leached. It would be better to add an exterior paint.
e. Higher the moisture content in the wood, better the result.
f. Harvesting time to treatment time need to be controlled.

GENERAL APPLICATION INSTRUCTIONS:

The lumbers are soaked in the preservative as an aqueous solution. Depending on the end use, the borate pressure treated wood may also be dried after treatment. Borates have been proven effective against all known wood destroying organisms (Carr, 1959; Barnes et al., 1989). DOT has been used to protect historic wooden structures and artifacts.

INFRASTRUCTURE REQUIREMENT:
i) Treatment Pond:
The most important item in the DOT treatment is the treatment pond. The treatment pond could be constructed of concrete, timber, etc. but the most significant part is that the pond needs to be water resistant. Proper water proofing mechanism is to be carried out so that the chemicals inside the pond do not leak and the exterior water do not percolate inside. Sheds to cover the pond is also required. The shed is provided to ensure that no rainwater or any other un-required agents enter the pond. These can be made as per requirement.
ii) Storage Area:
Ample amount of storage area is required. The areas could be classified as pre-treatment area and post treatment area. The size and space could be determined as per the amount of the wood consumption in the area. Other factors such as population, consumption ratio, availability of space etc. plays its role.
iii) Plastic Cover:
For the diffusion procedure, the treated timbers need to be properly covered so that no external environmental connection is there. For such procedure, a high gauge plastic sheet could be used which shall cover the treated timber for couple of days as per requirement.
iv) Chemicals:
The quantity of chemicals depends on the solution that is planned to prepare and the concentration of the solution as well. The chemicals that are required are as follows: For Solution: Boric Acid, Borax, Water For Quality Control + Testing: Salicylic Acid, HCL Acid (34%), Turmeric, Ethanol.

STEPS in DOT TREATMENT:

The method consists on soaking the
wood pieces into a prepared solution
for a proper impregnation. For an
easier and reliable process, a soaking
tank is required.
Dilution: For the preparation of the
solution, Boric acid and Borax is used
in the ratio of 2:3 in 28 kg of water.
For the treatment of 1 cu.m. of wood,
quantity needed as Boric acid 2.33 kg,
Boric acid 3.525 kg, Water 32.9 kg.

Temperature of 20-30 degree Celsius
is desirable.
Soaking: The wood pieces are put in
the tank carefully so that it does not
damage the plastic. Each batch of
wood is soaked for at least 30 minutes.
After 15 minutes, the wood is turned.
Thereafter, second batch of wood is
soaked and treated.
Dripping: Some wood laths are put
over and across the tank and the
wood pieces are laid over them, after
removing them from the tank, so that
they might drip back into the tank. The
dripping is done for about 3-5 minutes
and proceed to stocking.
Stocking: The treated wood is laid
over a flat surface, separated from the
ground by some wood laths and slightly
apart from each other. When stocking
another layer, 1” gap should be left.
Diffusion: It is during this phase
that the solution penetrates deep
inside the wood through osmosis.
Drying too fast can result in a bad
diffusion process, which means only
the surface gets treated. Therefore,
the wood pieces are wrapped in
a waterproof plastic right from the
moment when they come out of the
soaking tank. The wood must then
stay wrapped at least 48 hour.
Quality Control: To set up quality
control, it is necessary to determine
the penetration and retention of
the wood preservative. For this,
samples from the stock have to be
cut at certain length exposing crosssection.
The cut ends will be sprayed
with a mix of Dye and Revealer. The
wood parts where the preservative
has penetrates becomes red, but
those where there has not been
proper diffusion remain with wood’s
original color.

WHY DOT:
- F ire Resistant
- Water Resistant
- L east Toxic to humans
- E nvironment Friendly
- C heaper
- E asy to understand and use.
PRECAUTIONS:
Store in a dry place. Do not store
where children and / or animals may
gain access. Wastes resulting from the
use of this product may be disposed
of on site or at an approved waste
disposal facility.
CONCLUSION:
DOTs are especially good wood
preservatives for the protection of
wood from decay fungi and a wide
variety of insects, including all species
of termites. The single drawback is
that they can also be readily leached
from wood under certain conditions.

REFERENCE:
Ahmed, B.M., French, J.R.J and Viden, P. 2004. Evaluation of borate formulations as wood preservatives
to control subterranean termites in Australia. Holzforschung 58 (4) 446-454.
Barnes H.M., T.L. Amburgey, L. Williams, and J. Morrell. 1989. Borates as wood preserving compounds.
The status of research in the United States, Internat, Res. Group on Wood Pres., IRG / WP/3542.
Campora C.E. and Grace, J.K. 2007. Foraging Behavior of the Formosan Subterranean Termite
(Isoptera: Rhinotermitidae) in response to borate treated wood. International Research Group on Wood
Preservation. IRG/ WP 07-10605. IRG Secretariat, Stockholm Sweden.
Carr D.R. 1959, Boron as a Wood Preservative, Record of the Annual Convention of the British Wood
Preserving Association.
Dickinson, D.J. 1996. Remedial treatment; in situ treatments of historic structures. In: First Annual
Conference on Wood Protection with Diffusible Preservatives and Pesticides, p. 87-90. Forest Prod.
Soc., Madison, Wis.
Llyold, J.D. 1998. Borates and their biological applications. International Research Group on Wood
Preservation. IRG / WP 98-30178. IRG Secretariat, Stockholm Sweden.
Tokoro, M and Su, N. 1993b. Oral toxicity of TIM-BOR, Bora-Carea, boric acid and ethylene glycol
against the Formosan subterranean termite and easter subterranean termite. International Research
Group on Wood Preservation. IRG/WP 93-10045. IRG Secretariat, Stockholm Sweden.
Tsunda, K., Byrne., A., Morris, P.I., Grace, J.K. 2006. Performance of borate-treated lumber in a protected,
above-ground field test in Japan. International Research Group on wood protection. IRG / WP 06-30395.
IRG Secretariat, Stockholm Sweden.
www.asfnepal.org


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