Measuring cracks with tell tales

By The Helpful Engineer / On / In Existing Building Issues

Crack Monitor

Engineers can be requested to assess existing cracking in buildings. When doing this it is important to establish whether the crack is increasing in size. The best method for measuring crack movements is by use of a crack monitor or ‘tell-tale’. There are various types:

Crack monitors types. The most popular type is made with two slips of overlapping plastic plates with a red cross on one and a marked grid on the other, see picture above and below. Once this monitor is fixed in position an initial reading is taken. Then more readings are taken at regular intervals to establish if movement is occurring and if so, at what rate. By comparing the different rates of movement for cracks at different locations in a building, the cause and location of the weakness can be established. The monitors should be left in place for as long as possible to establish whether the crack is moving or not, and for a minimum of eight weeks.

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