The Situation
The property was a residential estate in Rivonia, Sandton — a large stand with approximately 80 linear metres of precast boundary wall dating back to the original construction around 2003. The homeowner had purchased the property two years prior and, faced with a wall that appeared black, green, and deeply stained, had been getting quotes to have it demolished and rebuilt.
A neighbour referred her to us. She was sceptical — a fair response to a wall that had clearly seen two decades of accumulated neglect.
The Assessment
Walking the perimeter with the homeowner was illuminating — for both of us. What she interpreted as irreparable damage was, in fact, almost entirely surface contamination. Precast concrete panels age very well structurally; their weakness is surface biology.
We identified the following on this wall:
- Black lichen covering approximately 70% of the surface — the dominant contamination type. This is what made the wall appear damaged beyond repair. Lichen is tenacious but removable.
- Green algae in the shaded northern sections and at the base where overgrown garden beds had held moisture against the panels for years.
- Heavy efflorescence on the lower two courses across most of the perimeter — white salt deposits driven by years of moisture movement through the base courses.
- Old paint on a 4-metre section near the main gate — a previous owner had painted part of the wall with exterior masonry paint at some stage. It was now peeling and bubbling.
- Minor hairline cracking in three panels — typical weathering for panels of this age, nothing structural.
Not a single panel needed replacement. The substrate beneath the contamination was sound. The "damage" was entirely biological and chemical — which meant it was cleanable.
The Treatment Plan
Given the severity and age of the contamination, we knew standard pressure washing would not be sufficient. We planned a multi-stage treatment:
Day 1 — Chemical Pre-Treatment
The full 80m perimeter received an application of concentrated biocide. Given the depth of lichen colonisation, we applied at double the standard dilution and left it for a full 18-hour overnight dwell. This was not optional — attempts to pressure wash deeply embedded lichen without adequate chemical pre-treatment simply blast the surface without addressing the root system, and the lichen regenerates within two to three months.
The peeling paint section received a specialist paint stripper application, also left to dwell overnight.
Day 2 — Wash Phase
We started on the paint section first. After overnight dwell, the stripper had lifted 90% of the old masonry paint — the residue came off cleanly with a 2 500 PSI wash. The underlying concrete was exposed and in surprisingly good condition; the paint had actually protected that section from biological colonisation.
Moving around the perimeter, the lichen came away dramatically after the overnight biocide treatment. We worked at 2 800 PSI on the most heavily colonised sections, reducing to 2 000 PSI on the cleaner areas to avoid unnecessary surface abrasion. The green algae at the base required a second biocide application and a 30-minute dwell during the wash phase.
The efflorescence was treated with our mild acid efflorescence remover applied by brush, allowed to react for 20 minutes, then neutralised and rinsed. The white deposits dissolved almost completely on contact. Some sections required a second application on the deepest staining.
The Result
By mid-afternoon on day two, the wall was complete. The homeowner's reaction — "I thought this was impossible" — is one we've heard before on heavily neglected walls, but it never gets old. The original grey precast concrete was fully visible for the first time in years.
The three hairline-cracked panels were sealed with a flexible concrete filler as part of the service, and the full perimeter received a penetrating silane sealer to slow future recontamination.
The Cost Comparison
The homeowner had received quotes to demolish and rebuild the wall ranging from R120 000 to R180 000. The full restoration — including the specialist treatments, two days on site, crack filling, and sealer application — cost a fraction of that. The wall will now require only standard annual maintenance going forward.
This case illustrates something we see regularly: property owners assuming a neglected wall is beyond saving when, in almost every case, it isn't. Before you demolish, get an assessment.
Key Lessons from This Job
- Age alone doesn't determine whether a precast wall can be restored — the structural condition does. Most walls installed from the 1990s onwards were built with quality precast panels that will outlast most finishes.
- Black lichen reads as catastrophic damage to the untrained eye. It's not. It's biology — and it's removable.
- Extended chemical dwell time is non-negotiable on deeply contaminated surfaces. Overnight dwell produced dramatically better results than a same-day wash would have.
- Restoration followed by sealing is the most cost-effective path in almost every case. A sealed, restored wall costs less than replacement and will perform well for years.
Think your wall is beyond saving? Get a free assessment from us first — in most cases, you'll be pleasantly surprised.