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External Wall Insulation Maintenance & Repair Guide: Fixing Common EWI Failures

Maintenance Summary

Most EWI systems are designed to last 30–50 years, but require an annual visual inspection. Common issues like algae growth and hairline cracks are usually symptomatic of poor drainage or minor building movement. Using specialized renovation products like Ceresit CT 98 (algae remover) and Ceresit CT 34 (mineral repair putty) can restore a system without a full costly re-render.

Common EWI Failures & Solutions

Failure Type Symptom Immediate Fix Long-term Prevention
Organic Growth Green/Black Algae streaks Apply Ceresit CT 98 Biocide Improve guttering; trim nearby trees
Hairline Cracks Fine "spiderweb" lines Clean and seal with Silicone Filler Annual wash to prevent dirt ingress
Impact Damage Holes or "dents" in render Patch with CT 85 + Mesh strip Install protective plinths in high-traffic areas
Joint Failure Gaps around windows/pipes Remove old caulk; apply high-grade Sealant Inspect sealant every 2 years

How to Repair Cracked or Damaged EWI Render

If your insulation system has suffered a crack larger than 2mm, a simple patch is not enough. You must restore the "Weather-Tight" seal:

  1. Diagnosis: Tap around the crack. If it sounds hollow ("blown"), the render has detached from the insulation and may need a larger patch.
  2. Preparation: Remove loose debris with a soft wire brush. Clean the area using a low-pressure wash.
  3. Reinforcement: For larger repairs, apply a layer of Ceresit ZU, CT 85 or CT 87 adhesive. While wet, embed a strip of Alkali-Resistant Fiberglass Mesh.
  4. Priming: Once dry, apply Ceresit CT 16 Primer. This ensures the new render matches the suction of the old wall.
  5. Finishing: Apply a topcoat of Ceresit CT 74 Silicone Render. Use a plastic float to match the existing texture (e.g., 1.5mm grain).

The Homeowner Maintenance Checklist

  • Bi-Annual Gutter Check: Ensure no water is "cascading" down the render.

  • Soft-Wash Only: Do not exceed 60 bars when using a high-pressure jet wash on silicone render, as it can drive water into the insulation.

  • Avoid "Ladders on Walls": Always use ladder "socks" or spread the load with a timber batten to prevent crushing the EPS insulation.

  • Check Window Sills: Ensure the "drip edge" of your window sills is clear of debris.

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