Masonry Works

Protecting Windows and Doors from Masonry Works

Skilled masons know that the brick, stone, concrete, plaster and mortar they use to construct durable buildings require considerable care to prevent them coming into contact with and damaging, other building materials prior to the building being completed.

This article outlines some of the common issues relating to damage from masonry construction and provides suggestions on how to avoid expensive claims for damage.


There are four main ways that mortar attacks building materials:

  1. Direct mortar contact:
    • Cement mortars can be strongly alkaline. (caustic) Contact with the skin can cause severe skin burns and other serious health problems. Ignoring a cement burn can end in amputation of the affected limb.
    • Alkaline cement will attack ordinary paintwork causing it to discolour. Strong alkaline mortar acts like paint stripper on surface coated finishes.
    • Alkaline cement can attack metals, for example:
      • Aluminium
      • Copper
      • Lead
      • Zinc
      • Attacks on these metals can occur over a longer period of time if the building design does not adequately protect these materials by using the correct protection sealants and flashing designs.
  2. Water run-off from cement surfaces
    • Rainwater, running over mortar and plaster surfaces dissolves the aggressive alkaline chemicals. The dissolved chemicals in the run off water can quickly corrode the metals they come into contact with. The longer the contact period, the more severe the corrosion will become. A frequent washing regimen should be implemented for all external surfaces on the completed building.
    • Alkaline cement in water run-off can irreparably damage powdercoated and anodised surfaces. For example windows, doors, garage doors, fascia, and flashings.
    • Alkaline cement in water run-off, can irreparably damage expensive glass.
  3. Abrasion
    • Brick, stone, concrete, plaster and mortar can remain dusty and gritty for sometime after construction is complete. Extreme care should be taken to ensure that other building products are not scratched as a result of transferring grit from the masonry products onto other building surfaces.
    • Glass is particularly susceptible to scratching. Glass can be damaged from grit embedded in cleaning cloths that have been used to wash other dusty, gritty surfaces.
    • Pre-finished aluminium, either anodised or powder-coated is susceptible to scratching from grit contained in cleaning cloths. To avoid scratching on joinery and glass, spills are best hosed off opposed to wiping with a cloth.
  4. Acid Wash
    • Some masons use an acid wash to remove unsightly mortar splashes from completed masonry work. Hydrochloric acid based washes break down the cement splashes which have occurred during the mortar process, enabling the splashes to be removed by hosing. This leaves the bricks in a clean condition.
    • However, acid washes are extremely corrosive to many metals and surfaces and will attack powder-coated, anodised and glass surfaces. Some specialty glasses have invisible metal oxide surfaces which control solar radiation, preventing the solar radiation from entering the building. Acid washes can destroy this expensive solar control coating leaving it in a visually marked condition.

Good Trade Practice

Masons, plasterers and painters can protect themselves from builder and owner damage claims by taking sensible and practical precautions.

Inspect and record

Good practice includes; a detailed inspection, recording, and agreement on existing damage, before any work commences and a final inspection at the conclusion of the work carried out.

Mask and protect

Before work commences all windows, doors, balustrades, rails and other at-risk items should be masked by competent tradespersons. The masking should not be removed until the work is fully completed. This includes sealing and painting of all mortar surfaces over which surface water will flow onto vulnerable construction components – e.g. Powder-coated and Anodised surfaces and glass.

Regularly check the masking for damage as torn or loose masking will not achieve adequate protection.

Only use masking tapes that have test reports demonstrating compliance with the performance requirements of the Window Association of New Zealand Test Methods for Protective Tapes and Films for use on Powdercoated Aluminium Joinery.


Exercise great care with acid wash and never use it above or near a window, door or balustrade.

After removing all masking products, the requirement for cleanup should be minimal. Physically touching the windows and glass should be avoided as much as possible. Instead use a low pressure hose to “soak” the window. Use a gentle window washing brush and mild detergent (pH neutral dish wash) as required. Finally rinse with clean water.

After ensuring the clean window has no grit remaining, a squeegee can be used to remove the residual water film.

Do not use cloths that might contain or transfer grit - as they will scratch the glass as well as the powder-coat and anodised finish.

Under no circumstances should scrapers be used on glass or powder-coat and anodised surfaces.


Insurance companies are reluctant to settle claims for damage due to avoidable masonry related damage. This page is written in response to an insurance industry request for increased industry awareness of the issues.