The majority of high rise framed buildings in the UK were constructed after 1960. Many utilised cavity brickwork panels to form flank walls and under window panels, although some solid brickwork panels can be found on occasion. This brickwork often incorporated brick slip construction on floor beams over door and window openings. In general, if properly constructed and maintained, such cavity brickwork has performed well over the years, although there have been some notable exceptions. The most commonly found defects include cracking, bowing of brickwork, failure of brick slips, dampness and brick face spalling.
These defects can be attributable to a range of causes, including thermal/moisture (hygrothermal) movement, poor fixing and construction details, shortening of the concrete frame due to shrinkage and creep, etc. and general “wear and tear” over the years. Subsidence/settlement problems are rare on high rise buildings which usually have major conservatively designed foundations to carry the large loads involved.
AWT have extensive experience and expertise in the diagnosis and repair of such defects, using both long established proven techniques and newly developed solutions. Repairs are always undertaken with care and attention to detail by trained and highly skilled operatives.
Upon instruction AWT will undertake surveys of the building’s infill walls (in association with or directed by engaged engineers), noting all visible defects and cavity deficiencies.
- Our surveyors will visually inspect the accessible external infill walls for surface defects, noting the presence of any brick slips, their condition and sounding.
- A cavity inspection will establish the wall tie density, type, condition and embedment to show the effectiveness and predicted life of the existing ties in accordance with BRE 401.
- The cavity inspection will also establish whether there is any building debris present in the space, bridging the cavity and therefore impeding its effectiveness.
Subsequently a clear, simple report will be prepared, detailing any defects that were found and the most likely causation. Where applicable the report will also provide remedial works recommendations and quotations or budgets.
COMMON DEFECTS – CAUSATIONS AND REMEDIES
- Wall tie deficiencies
- Cause: Corroding or low density of ties together with inadequate embedment.
- Remedy: Installation of a recognised pattern of supplementary remedial ties and, where appropriate, the isolation of old ties.
- Wall tie treatment – Generic repair
- Failing/de-bonding brick slips
- Cause: Often poor fixing specification and/or lack of soft joints, leading to compression failure following concrete frame shortening.
- Remedy: Replace and re-bed as necessary, fix slips using mechanical fixings, and as necessary form soft joints, or complete removal and replacement with alternative material.
- Cracking in brickwork
- Cause: Often associated with inadequate movement joints and hygrothermal movements.
- Remedy: Introduction of movement joints properly designed to accommodate cyclic movements.
Note! Care should be taken when appraising calcium silica bricks, which have movement characteristics different from those of fired clay bricks.
- Horizontal cracking to bed joints
- Cause: Commonly associated with wall tie corrosion.
- Remedy: – Wall tie treatment – Generic repair.
- Corroding embedded steel causing brickwork cracking [e.g. Rebar/steels over openings]
- Cause: Moisture ingress/rusting.
- Remedy: Either exposure and treatment of steel, or removal of steel and provision of alternative support mechanism.
- Bowing brickwork
- Cause: Often associated with lateral restraint deficiencies and/or concrete frame shortening.
- Remedy: Introduction of a recognised pattern of supplementary remedial ties. Where severe, local rebuilding.
- Concrete frame shortening effect
- Spalling bricks/poor pointing
- Cause: Frost action and general erosion (but beware of crypto-efflorescence failure!).
- Remedy: Traditional brickwork replacement and re-pointing to match existing.
- Brickwork dampness
- Cause: Mainly attributable to defective or missing DPCs/cavity trays and/or cavity bridging with debris from the original construction. Often exacerbated by lack of cavity ventilation.
- Remedy: Cavity cleaning often combined with insertion of new cavity trays and weep holes, to improve cavity ventilation.
All proposed brickwork remedial works are individually designed to provide a durable cost effective/best value repair through the introduction of stainless steel bed joint reinforcement, beaming, lintel repair, lateral restraints and resin bonded ties to reinstate continuity and structural integrity.
Spalled bricks, pointing and damaged brickwork – AWT’s experienced and professional operatives have all been trained to the highest level. They are skilled in carrying out their work in a manner that is sympathetic with the current building, and will always attempt to match replacement bricks and utilise a pointing style and mortar mixture that blends in with the existing texture and colour.
Case studies and generic repairs: