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We have a bamboo garden in the terrace area, fully surrounded with Bessent blocks and concrete base with 2 drain holes through the base. The inside was layered with a black membrane for water proofing. However the water proofing hasn’t worked and the garden leaks at the base. The garden was installed approximately 5 years back and started leaking around 1.5-2 years back and now I’m finally got around to fixing it or at least trying to.
ive heard using cor flute is not effective as the roots will work around it and spread into the ground. I was advised to use it (I have a plentiful supply) but sikaflex each sheet so that it is fully sealed and as I have so much for flute I thought to do a double layer and maybe a third.
Question: will this idea stop the leak? Forgot to mention my thoughts on why the leak started - 1 some minor ground movement cracked the membrane or it failed some other way. 2 the invasive root system burrowed through the membrane. Appreciate your help, Greg
Welcome to the Bunnings Workshop community @Greg11. It's brilliant to have you join us, and many thanks for your question about sealing a raised garden bed.
The first thing I’d check is whether the drainage system is still working effectively—if it isn’t, water will pool and eventually find a weak spot to escape through, especially if the outlet pipes are sitting higher than the base. If that’s the case, consider lowering the outlets so water can drain before it starts accumulating. I'd also recommend laying at least 100mm of coarse aggregate at the base to help with drainage, and placing a drain mat or geotextile fabric over it to stop soil from clogging things up over time.
As for addressing the leak, your theory about ground movement or root penetration causing the waterproofing to fail is likely spot-on. Rather than relying on multiple layers of corflute—which, even when Sikaflexed, may still allow water to seep through at the joins—I’d suggest a more robust fix. Start by sealing any visible cracks with Sikaflex, then apply a couple of coats of a good-quality waterproofing membrane over the entire interior. After that, lay Builders plastic over the top as an extra barrier. That combination should give you far better protection and reduce the risk of future leaks.
Please let me know if you have any questions.
Mitchell
