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Deep Retaining Wall
Every now and then, a treatment is found to be not constructed as could have been reasonably expected. We have a client's home on Brisbane's northside where termites had previously attacked the home and been treated by another firm. When we first visited the home, termites were visible coming up the brickwork at the front door.
The home is about 30 years old, and is a brick and weatherboard cypress pine framed home on a concrete block base to three sides. The external soil/slab height was level with the upper floor at the front, and below the lower level at the rear. The concrete block wall was constructed of "standard" blocks, and concrete filled (not termite proof). With a wall constructed of "standard" blocks, the cores of the blocks fill with concrete, but the mortar joints don't. With a concrete block wall constructed using "H" blocks, the gap between the mortar joints is filled with concrete. An ant cap was near the top of the wall, but compromised by the external soil/slab height at the front.
Our first advice was that we didn't trust the ant capping, and we didn't trust the wall. We could break the concrete at the front, and treat to the ant capping by a soil replacement technique, and using Biflex as the termiticide. If termites persisted, we would need to treat to the footings. This top section was done, and termites persisted, attacking a section of pine flooring. These were dusted with Bayer Intrigue.
With termites being so persistent, our original recommendation to treat to the footings was being seriously considered. We offered our termite bait boxes as a possible alternative to aggressively bait the termites. Our client accepted our quotation to trench to the footings. With downstairs being less than legal build in height, we had assumed in our quotation a footing depth of 2 metres. With a major excavation, we recommended using Granitgard as the termite protection method, as this carried a ten year warranty, and is considered a "life of building" product. We weren't planning on ever digging this again.
With the planned trench being deeper than our excavator could reach, we planned to dig the excavator in approximately 750mm to get the machine within reach of the footings at the front wall. This would have resulted in us removing approximately 11 cubic metres of soil at the front wall to get us within reach of the footings.
We had the concrete slab cut, and broke the concrete. We got down about 600mm, and found another concrete slab laid under the other slab. This was cut and broken. We got down a bit further, and discovered a ball of concrete (app 1.5 m3) had been poured behind the wall that had to be broken and removed. We got down a bit further, and found logs buried behind the wall. We started looking for the footings, and we could not reach the footings from our excavated position. We dug the excavator in another 500mm, and still could not find the footings. We dug the excavator in another 500mm, and still could not find the footings. We dug the excavator in another 500mm, and still could not find the footings. We dug the excavator in another 500mm, and finally found the footings some 3.6 metres (18 concrete blocks) below finished soil height. 31 cubic metres of soil was removed to allow us to get the excavator within reach of the footings at the front wall alone.
The drawings above show what we went through to get where we did. The finished article has the wall treated with blackjack, Granitgard, root barrier, drainage gravel, and then a geotextile fabric to keep the soil from affecting the drainage gravel. Filtered sock aggi pipe drains the wall. This should last an extremely long time.
The
client in this case has become a true victim of the termite issue. Had this
treatment been undertaken while the organochlorine termiticides were still
available, treatment of the front wall most likely could have been completed for
less than $1,000.00 by drilling and injecting through the wall, and then
addressing waterproofing issues. This would have produced a positive result for
30-35 years. Because of the limitations of modern termite protection methods, we
have had to treat this home by the invasive means we have. The client has no
recourse against the builder, whose construction methods were effectively
addressed by the termite protection methods available at the time.
There are some lessons to be learnt from this treatment. We cannot accurately predict how long a treatment is going to take when we have to go underground. We cannot accurately predict what is under the ground. We can, through a reasonable knowledge of building practices have some expectations, but buildings are not always constructed in accordance with good building practices.
For more information, please don't hesitate to contact us at any time. © Mark Porter 2002
Get it right the first time!
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