The Science Behind Concrete Tank Degradation
- Jun 19
- 2 min read
Rainwater is naturally slightly acidic (usually a pH of around 5.6) because it absorbs carbon dioxide from the atmosphere, forming a weak carbonic acid. Concrete, on the other hand, is highly alkaline. It relies on calcium hydroxide (lime) to maintain its structural strength and integrity.
When acidic water sits inside a concrete tank, a chemical reaction occurs:
Lime Leaching: The acid in the water reacts with the calcium hydroxide in the concrete, neutralizing it and dissolving it into the water.
Micro-cracking and Pitting: As the lime leaches out, the concrete becomes increasingly porous. The smooth internal surface begins to wear away, leading to pitting, rough patches, and tiny structural cracks.
Structural Weakening: Over many years, if the water penetrates deep enough to reach the internal steel reinforcing mesh (rebar), the steel will begin to rust. Rust expands, causing the concrete to spall (flake or break away), which can eventually compromise the structural integrity of the tank.
Signs of "Old Tank Syndrome"
A gritty or sandy residue at the bottom of the tank (dissolving concrete).
White, powdery deposits or tracking lines on the outside of the tank where water is weeping through structural cracks.
Rough, exposed aggregate on the inside walls where the smooth cement paste has dissolved.
How to Fix and Prevent It:
You don't necessarily have to go through the massive expense and hassle of demolishing and replacing a very heavy concrete tank.
Installing a Tank Liner: Installing a polyethelyne tank liner acts as a complete physical barrier. It stops the acidic water from ever touching the concrete again, effectively sealing existing leaks and halting the leaching process entirely.
Tankman are experts at successfully installing liners to rescue leaking concrete tanks on Waiheke, having successfully installed 15 of these over the last year for Waiheke home owners. Give us a call to see how we can customise a solution for you. (Mention this blog in your booking process.)
116 Ostend Road, (next to Waiheke Workout)
www.tankman.co.nz - Book your tank clean digitally
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