EXPERT Subsidence · Further Knowledge · E2 of 6
Repair must match the wall material
This is the most common mistake — using a stronger repair than the surrounding fabric. Future differential movement that the wall would have absorbed cracks around the repair instead.
| Wall material | Appropriate repair |
|---|---|
| Random rubble + lime mortar | Rebuild local with same stone + flexible mortar |
| Soft brick + lime mortar | Cut out + renew, lime mortar match, PCC lintels / masonry reinforcement |
| High-strength brick + mortar | Epoxy resin injection or PCC lintels with equivalent strength match |
| Aerated thermal blocks | Match strength — common bricks or thermal blocks |
Helibar — the workhorse
Helical stainless steel rods grouted into bed joints. Five typical applications:
- Crack stitching — bars 500 mm either side of crack into mortar joints
- Reconnecting party walls to external walls — angled clearance holes, grout-injected
- Stabilising bowed walls into joist ends — power-driven through masonry into joist, resin-bonded
- Repairing separated masonry — ties through near leaf, 75 mm into far leaf
- Full-perimeter masonry beams — parallel reinforcing rods in bed joints, grouted, can stiffen walls enough to AVOID needing to underpin
Hoopsafe — the alternative to underpinning
Post-tensioned reinforced concrete beams "squeeze" the walls together so they resist differential settlement cracking. Requires uplifting ground floors but avoids excavation outside the building.
Contracts & statutory requirements
- JCT Minor Works Form or JCT Measured Term Form — most common
- Engineer = Contract Administrator
- CDM Regulations apply (when client = insurance company / panel contractors)
- Party Wall etc Act 1996 applies for any work on shared structure
Reinstatement of finishes
Equivalent present-day value — not original purchase value. £30/sq yd tiles bought 20 years ago must be replaced with today's £30+/sq yd equivalent. Where matching is impossible: re-render the whole elevation, or overpaint to disguise the patch.
Even emulsion paint must be replaced with the same standard.
Certificate of Structural Adequacy
The CoSA is a professional opinion that the repairs were appropriate to rectify the damage. It is NOT a warranty or guarantee. Transfer of benefit to a new owner needs the issuing expert's written permission and may require a re-inspection (chargeable).
Source: Subsidence Handbook 4th Edition, Chapter 7 — Superstructure Repairs.