BLD/Masonry/TBT-BLD-005

Cavity Wall Construction

Building & Structural Works › Masonry › Cavity Wall Construction

Presenter		Project
Location		Date

Cavity walls consist of an inner blockwork leaf and outer brickwork leaf separated by a cavity containing insulation.
Wall ties connect the two leaves and transfer lateral loads — missing, incorrect, or corroded ties cause wall collapse.
Insulation boards or batts must be installed correctly to maintain the thermal performance and fire resistance of the wall.
Partial fill insulation must be kept clear of the outer leaf to maintain the residual cavity and prevent moisture bridging.
Cavity trays, weep holes, and DPC layers must be installed at the correct positions to manage water within the cavity.
Mortar droppings accumulating on wall ties and cavity trays cause moisture bridging and blockage of weep holes.
Working at height from scaffolds during cavity wall construction requires the scaffold to be maintained and inspected regularly.
Manual handling of blocks, bricks, and mortar tubs is physically demanding — correct technique and mechanical aids reduce injury.
Cement in mortar causes chemical burns and dermatitis — waterproof gloves and barrier cream must be used throughout.
Cutting blocks and bricks generates silica dust requiring on-tool extraction or water suppression during every cut.

Structural stability	Wall ties are the structural connection between inner and outer leaves — missing or incorrect ties cause outer leaf collapse in wind.
Moisture penetration	Incorrect cavity tray, DPC, and weep hole installation allows water into the building — defects cost thousands to remedy.
Silica dust	Cutting concrete blocks releases respirable crystalline silica that causes incurable lung disease — dust control is mandatory.

Don't

Install wall ties at the correct spacing and type specified in the structural design.
Fit insulation tightly with no gaps and keep it clear of the outer leaf where required.
Install cavity trays, DPC, and weep holes at every position shown on the design drawings.
Keep the cavity clear of mortar droppings using cavity battens or boards during construction.
Use on-tool extraction or water suppression when cutting blocks and bricks.
Wear waterproof gloves and barrier cream when handling mortar throughout the day.
Check scaffold platforms and guardrails before starting each day of bricklaying.
Use mechanical aids for lifting heavy block packs and mortar tubs to working height.
Protect the top of unfinished walls from rain using polythene sheeting overnight.
Inspect wall tie embedment and mortar joints at the quality hold points.

DON'T omit or space wall ties wider than the structural design specifies.
DON'T leave gaps in insulation or allow it to bridge the cavity to the outer leaf.
DON'T miss cavity tray, DPC, or weep hole positions shown on the design.
DON'T allow mortar droppings to build up on ties and trays within the cavity.
DON'T cut blocks or bricks without dust extraction or water suppression in place.
DON'T handle mortar with bare hands — cement causes burns and permanent dermatitis.
DON'T use scaffolds without checking they are tagged safe and fully boarded.
DON'T carry heavy block packs up scaffolds manually when a hoist is available.
DON'T leave unfinished walls exposed to heavy rain — protect them overnight.
DON'T cover wall ties before they are inspected at the required hold point.

See also: Bricklaying Safety | Cement and Concrete Burns

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