ANTI-TERMITE TREATMENT OF FOUNDATIONS
The
subject of anti-termite treatment of buildings is usually divided into the
following three parts:
1.
Pre-construction measures to be taken
2.
Pre-construction treatment
3.
Post-construction treatment
IS 6313 Part 1 deals
with the general constructional measures to be taken, Part 2 deals with pre-construction treatment and Part 3 discusses post-construction
treatment (treatment of existing buildings). They give many constructional
features to be provided in buildings such as for godowns, etc. to reduce
termite attacks which we will not deal with in this book. Here we will consider
only pre-construction and post-construction treatments of ordinary buildings.
Termites in Buildings
Based
on their habitat, termites are classified into the following two types:
1.
Ground nesting or subterranean termites
2.
Wood nesting or non-subterranean termites
Ground
nesting or subterranean termites are more common in India and their presence in
and around a building is indicated by swarms of winged reproductions flying
from the soil or wood lying around the site just at the beginning of the
monsoon.
Wood
nesting or non-subterranean termites live in the dry wood inside buildings and
is recognized by their pellets of digested food or blisters on the wood surface
as the wood is eaten away. In their search for food, these termites damage not
only wood (cellulose) but also substances like rubber, plastic, underground
cables, etc. Both varieties can be terminated by the same anti-termite
chemicals.
Recommended
Chemicals for Treatment
Even though Aldrin, DDT and many
other chemicals were once prescribed in old IS codes, many of them were found
to be very toxic and leave toxic residues in the soil and ground walls which
give health problems over a period of time. Hence many of them have now been banned
in the new revision of the BIS code. The following emulsifiable chemicals have
now been recommended:
1. Chloropyrifos concentrate 1.0% by weight
2. Heptachlor concentrate 0.5% by weight
3. Chlordane concentrate 1.0% by weight
Chlorpyrifos in 1%
concentration by weight conforming to IS8944 (1978) is a popular chemical being
used. They are available with agrochemical agencies as they are used to control
termites in crops such as cotton, coconut, citrus, etc. Durmet is a brand name
of one of the chlorpyrifos available in the market in various concentrations. Another brand name is Dustban TC. These
can be diluted to form 1% concentration as desired in water for soil treatment
and in kerosene oil for treatment of wood.
Generally, 5 parts of Durmet 20
EC are diluted with 95 parts of water (or kerosene) to give an emulsion of 1%.
As the solution is toxic, if it comes in contact with the skin, it should be
washed out immediately with soap and water. The methods of treatment
(pre-construction treatment and post-construction treatments) are briefly
described below.
Pre-construction
Treatment with Durmet
A hand-operated pump is used for
uniformly spraying the chemicals at the specified rate. To facilitate the
right dose, graduated containers should be used. Treatment should not be
carried out when it is raining or soil is wet with subsoil water. It should
start when foundation trenches and pits are ready and just before concreting of
the foundation. The treated barriers for termites should not be disturbed after
treatment. The treatment is shown in Fig. below and is carried out in seven stages
as described further.
First stage: Treatment of wall trenches and basement excavation. As the first step, all
termite hills found at the site during site clearance should be sprayed with
chemicals. All surfaces of pits (sides
and bottom of wall trenches and basement excavations) should be treated to
a height of 30 cm from the bottom with the solution at the rate of 5 litres per
square metre of surface area.
Anti-termite treatment of foundation
and earth fill below the ground floor.
Second stage: Treatment of refill in contact with the foundation. All the
refilled earth in the excavation is immediately in contact with both sides of the
wall footing and all four sides of a column footing should be treated for a
distance of 30 cm (as shown in Fig. above) at the rate of 3 to 5 litres per
linear metre vertical surface of the wall. If water is used for ramming the
earth, then treatment should be done after the consolidation by rodding (making
holes) in the consolidated earth at close intervals of 15 cm close to the wall
or columns and applying the chemical close to the wall. It is preferable to
treat all the earth adjacent to the foundation for a width of 30 cm. Similarly
in framed structures, excavations for the plinth beams should also be treated.
Third stage: Treatment of soil below floors. The earthfill below the
floors up to the plinth level has also to be treated after the fill has been
made by putting holes 5 to 7.5 cm deep at 15 cm centres in a grid pattern and
filling the holes with the solution at the rate of 5 litres per square metre of the treated surface.
Fourth stage: Treatment of junction of floor and wall. Before laying
the subgrade, channels of 3 cm wide and 3 cm deep are dug along the junctions
of floor and wall and treated at 15 litres per square metre of wall surface by
putting holes 15 cm apart along the channel and allowing the chemical to
seep through to the bottom. The soil is tamped back in position after the
operation.
Fifth stage: Treatment of soil along the external perimeter of the building.
After the building is completed, holes are made along the external perimeter at
intervals of 15 cm and depth of 30 cm. These holes are filled with the chemical
emulsion at the rate of 5 litres per metre length of the wall.
Sixth stage: Treatment of other locations. Anti-termite treatment
should be made at expansion joints after the subgrade has been laid at 2 litres
per linear metre of expansion joint. Similarly, when pipes and conduits enter
the building, the soil around them for a distance of 15 cm and a depth of 7.5 cm
should be loosened and treated.
Seventh stage: Treatment of wood surfaces. It is also a good practice
to paint all fresh wood surfaces, such as door and window posts which will be
in contact with masonry, with two coats of the chemical in kerosene oil before
it is installed in the building.
Post-construction Anti-termite Treatment of Building
Foundation
For
post-construction operation, a pressure pump will be required for proper
penetration of chemicals into the surface to be treated. Proper checks should
also be made regarding the adequacy of the number of chemicals (chemicals
mixed with water) pumped in. The following procedure is usually adopted:
Treatment of foundation of outside
walls around the building. If there is no
apron, we make trenches 50 cm deep and equal to the width of a shovel, exposing
the foundation near the external walls. Holes 15 cm apart and 50 cm deep are
made by an iron rod. Emulsion at the rate of 5 litres per square metre of the vertical surface of the substructure is to be used for each side of the floor.
One-half of the quantity is pumped through the holes and the other half is
poured along the trench. If there is a concrete apron, 12 mm diameter holes are
dug as close to the wall as possible about 30 cm apart and the chemical is
pumped into these holes at the rate of 5 litres per linear metre. A similar treatment is to be made for column and plinth beams.
Treatment of soil under floors. For this purpose, 12 mm diameter holes 30 cm apart are
made deep enough to reach the soil below along the junctions of wall and floor,
along cracks in the floor and along the construction joints. The emulsion with
water is pumped into these holes to soak the soil or at the rate of one litre
per hole. The holes are then sealed with cement mortar 1:2. (The floor may
also be drilled and the ground below treated but this is a cumbersome process.)
Treatment of masonry at plinth level. The movement of termites through the walls can be
stopped by drilling holes in the masonry at plinth level at an angle of 45° on
both sides of the wall (and especially where wood such as door post is present)
at 30 cm centres. The emulsion is pumped till the masonry is soaked or at a
maximum of one litre per hole. The holes are then sealed with 1:2 cement
mortar.
Post-construction Treatment of Woodwork
In
post-construction, we may have to deal with buildings in which the woodwork
such as doors or fittings (such as shelves) have been attacked by termites
It
is better to treat woodwork with the chemical mixed in kerosene oil. Through this
process, we get better penetration of the chemical into the wood. First, the
masonry around the wood is treated with the chemical and secondly the wood
itself is treated by drilling 6 mm diameter holes at 15 cm intervals and
infusing it with the kerosene-based chemical. Two coats of the chemical can
also be applied to the surface of the wood before applying the paint.
Must read: Anti-Termite
Treatments For Types Of Construction Works
FAQ
Which chemical is used in anti-termite treatment?
1. Chloropyrifos
concentrate 1.0% by weight
2. Heptachlor
concentrate 0.5% by weight
3. Chlordane
concentrate 1.0% by weight
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