wall tie survey

Wall Tie Condition Survey

The role of a 1st Master Wall Ties surveyor is to collect and record data about the wall construction and the condition of the wall ties.  It is not to form any subjective opinion on the service longevity of the ties.  Once the ties have been inspected they are categorized in accordance with Table 2 of BRE Digest 401, which classifies the condition of steel ties by rating corrosion levels from 1 (uncorroded) through to 9 (total failure).

The survey report will then objectively identify the ‘Best’ and the ‘Minimum’ remedial measures based on the condition of the tie-irons, as laid out in Table 4 of the Digest.  This may range from a BRE recommendation that an inspection is carried out in a further 10 years (corrosion level 1) through to an immediate action to fit a wall tie replacement system (corrosion level 9).

The wall tie condition survey is carried out in 3 stages

Existing Wall Tie Spacing

  • A metal detector is used to locate the position of existing ties over an area of wall to establish whether the number of wall ties per square metre meets current building standards

Visual inspection of sample ties

  • A borescope is used to view randomly selected ties within the cavity, subject to the cavity being free from insulation or other blockage.
  • Localised areas of mortar are removed in the outer leaf to expose sample tie-ends. This allows inspection of the ties most vulnerable section, establishes the type of wall tie and permits measurement of its embedment depth.

General Observations

  • Composition of the walls on both sides of the cavity; brick, perforated brick, concrete block, timber frame, etc.
  • Width of the cavity at various points
  • Height of the building, its exposure level, wind-speed band and terrain, as identified in Table 5 of BRE Digest 401
  • Look for cracks in the walls and establish whether the cracks coincide with the positions of the wall ties
  • Identify bowing, leaning or undulation of wall surfaces
  • Any other defects that may be associated to the wall ties or that may contribute to increased corrosion risk (condition of bed joints, exposure to salts etc.)

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