Why Timing Your Clean Matters
Most property owners think about wall cleaning reactively — they notice the green patches in November and call someone in December. By then, the algae has had a full wet-season head start and the biological material is well-established. A reactive clean in summer costs more, takes longer, and requires harsher chemistry than a preventive clean in late winter.
The goal of spring preparation is simple: go into the wet season with walls that are biologically clean and ideally sealed. Algae needs three things to take hold — moisture, a surface to cling to, and spores. You can't control the rain. But you can control the surface conditions.
August to mid-September is ideal for a pre-season clean on the Highveld. Walls are at their driest after winter, biological growth is at its lowest density, and you have time to apply a sealant before the first rains hit.
The Five-Step Spring Preparation
1. Full Visual Inspection
Walk your entire perimeter and note: any new cracks that opened over winter, areas where vegetation has grown up against the wall (roots hold moisture), blocked drainage gaps in the base course, and any sections that have existing biological growth that made it through winter. Photograph everything — it's useful for tracking changes year over year.
2. Clear Drainage and Base Vegetation
Weep holes and base drainage gaps in precast walls are there for a reason: they allow moisture that collects at the foundation to escape. If they're blocked with compacted soil, roots, or debris, that moisture has nowhere to go — it wicks up into the panels. Clear these out before the rains come. While you're at it, cut back any vegetation growing within half a metre of the wall base.
3. Professional Pressure Wash
A proper pre-season wash with biocide treatment addresses existing biological growth at the root level, removes winter dust accumulation, and exposes the surface for sealant application. Don't use a garden hose for this — for an effective pre-season treatment, you need chemical dwell time combined with professional washing equipment to fully remove spore populations from the surface texture.
4. Spot Treat Any Cracks
Small hairline cracks in precast panels are a moisture entry point. In dry winter conditions, they sit dormant. The first spring rains drive water in, which carries biological spores deeper. Before the rains, fill hairline cracks with a flexible, paintable concrete sealant. This isn't a structural repair — it's a moisture management step.
5. Apply a Penetrating Sealant
A silane/siloxane penetrating sealer applied to clean, dry walls creates a water-repellent layer within the concrete matrix — invisible to the eye but highly effective at slowing re-contamination. Sealed walls repel the moisture that algae spores need to germinate. In our experience, sealed walls stay clean two to three times longer between services. Apply only to thoroughly dry walls — ideally allow 48 hours after washing before sealing.
Your Pre-Season Checklist
- Walk the full perimeter and photograph any cracks, staining, or damage
- Clear weep holes and drainage gaps at wall base
- Cut back vegetation within 0.5m of the wall
- Book professional pressure wash with biocide treatment
- Fill any visible hairline cracks with flexible concrete sealant
- Apply penetrating sealer to clean, dry walls (48 hrs post-wash)
- Note any areas of persistent efflorescence for monitoring
What Happens If You Skip the Prep
The first heavy rains of October will rehydrate any residual algae spores on your wall surface. Within four to six weeks, you'll see green patches forming in shaded areas. By December, heavy colonisation is typical on walls that went into the season with an existing biological load. By February, you're dealing with a full remediation job rather than a maintenance clean — a significantly larger cost and effort.
Pre-season prep is the single most cost-effective thing you can do for your walls. Book your August or September clean now before the diary fills up — this is our busiest window of the year.