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Concrete Block Retaining Wall
Early concrete block walls are notorious for allowing termites into a building when used as an internal retaining wall. The early concrete block walls were commonly constructed of standard blocks (like a figure 8), and when filled with concrete, the cores would fill, but the mortar joints between would not. Termites could easily pass through the mortar joints. Our Large Retaining Wall page shows a very good example of how it can go wrong, and the effort it can take to correct.
Later block walls are commonly constructed of H blocks, which when filled with concrete, completely fill, and form a solid masonry wall. Ideally, where standard blocks are used at returns and ends, then the appropriate webs should be cut from the blocks to form H blocks. Credit to John Callow of Callow Constructions for this one.
In 25 years of termite experience, we've never seen a H block wall filled during construction fail from a termite perspective, and to our view these walls only need termite protection at any articulated joints, and where slabs are joined (top, bottom, or part way up the wall). The better certifiers are now starting to accept this under the performance provisions of the Building Code, but with individual cases, please check with your own certifier. We'd love to see the block manufacturers come up with some formal testing and certification, but it seems to be in the too hard basket at the moment.
If the earlier concrete block walls are failing from a termite perspective, a new termite protection method is a Granitgard product called Blockaid. It's a bitumenous based product applied by a priming coat, a bitumenous coat, a reinforcing fabric, and a second bitumenous coat. Being bitumenous, Blockaid comes in any colour you want, as long as it's black, but it's a product that can easily be installed retrospectively, and in keeping with the Granitgard tradition, we expect Blockaid to be an extremely durable product in the long term.
Granitgard's Blockaid is covered by CSIRO Technical Assessment 314 - May 2004, and is available for download at http://www.cmit.csiro.au.
For more information, please don't hesitate to contact us at any time. © Mark Porter 2004
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