Our complex hasn’t put a lot of emphasis on power washing the concrete common areas. That’s a mistake. Here’s why.
When you first think of concrete, you think of something that lasts a long time, is solid, and seems to need very little maintenance. That’s not actually the case.
Concrete is rough. This is great for doing what it’s meant to do, but when it comes to moisture, it’s a problem. Those micro pits and bumps trap moisture. This moisture then causes algae growth.
The problem of algae on concrete
Algae growing on concrete may look like a minor cosmetic issue at first. But over the long term, especially in a damp climate like coastal British Columbia, it can cause progressive structural, safety, and financial consequences. Here’s a breakdown of the real long-term impact:
Surface Deterioration & Scaling
Algae thrives in moist, shaded environments. It traps water against the surface of the concrete. Over time this causes increased moisture absorption. Since water expands when frozen, this leads to freeze-thaw damage of the concrete itself, causing it to get crumbly and unstable. It also leads to micro cracks that spread, as well as surface scaling.
Concrete is porous. When algae holds moisture against it continuously, the surface breaks down much faster than clean, dry concrete.
It only takes 3-5 years of neglect to cause surface scaling and deterioration.
Accelerated Structural Weakening
Long-term moisture retention does more than just damage the surface. When water penetrates deeper, it reaches reinforcing steel rebar. This applies to areas such as the concrete stairs in our complex, which are strengthened with rebar. As a result, rebar begins to corrode. Rust expands up to 6–7 times the original volume. This internal pressure causes cracking and spalling. Ultimately, the stairs become unsafe. The process is slow, but once corrosion begins, repair costs increase dramatically.
What started as algae can eventually require concrete resurfacing, partial slab replacement, and expensive structural repair.
Reduced Aesthetic & Property Value
Neglected concrete looks poorly maintained. It signals to prospective buyers that the property is not being regularly maintained, reducing perceived property values. This negatively impacts all owners by affecting resale appeal.
Preventative maintenance is dramatically cheaper than structural repair, especially in damp, coastal regions like BC. Given the damp climate, algae regrowth is faster, and freeze–thaw cycles amplify damage. North-facing surfaces are high-risk, and the concrete in shaded, poorly drained areas deteriorates fastest. This includes the areas to the east side of the complex where we have lots of shade trees.
Slip Hazard & Liability Risk
Algae becomes extremely slippery when wet. Long-term neglect increases the risk of slip-and-fall accidents, with the corresponding insurance claims. There is the potential for legal liability for strata properties. Thus, this becomes a risk management issue, not just a maintenance issue.
Proper maintenance is especially important for walkways and the 28 concrete entry steps in our complex.
Organic Acid Damage
Algae and moss can produce mild organic acids as they decompose. These acids slowly break down cement paste and increase porosity. That organic process makes future moisture penetration easier. It’s a compounding effect:
More algae → more moisture → more breakdown → easier regrowth.
Bottom Line
Algae on concrete is not just cosmetic. If neglected, it leads to surface breakdown, structural weakening, slip hazards and liability, accelerated moisture damage and higher repair costs.
The longer it’s left untreated, the more expensive the solution becomes.
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