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Building Conservation: Specialist Surveys |
Often, inspections can cause more damage than the decay agent. Non-destructive inspection techniques allow EBS to survey buildings in great detail whilst causing minimal damage to the fabric. Fibre optics, non-invasive moisture metres, micro drilling with the Resistograph and other techniques allow accurate diagnosis, reducing the amount of destructive opening up saving a considerable cost.  A fibre optic borescope allows inspection into hidden voids without the need to open up. A 10mm diameter hole is drilled through the material that is to be investigated, or the borescope is inserted through existing gaps. The void can be visually inspected or recorded by camera or video. Non-invasive moisture meters provide a useful method of testing the moisture content of materials. They are most accurate in timber, and give warning of the decay potential. Readings in masonry and plaster require the skills of an experienced operator, as certain finishes can give false readings. The presence of salts can also influence the readings and give a false impression of dampness. Non-destructive Inspection with Resistograph E400m (1410): EBS carries out non-destructive investigation of timbers with the state of the art technology "The Resistograph". This instrument was developed in Germany. The principle is based on the torque resistance of the Resistograph related to density of the timber, which is then printed on a computer graph. The decayed section can be analysed from the computer printout graph. The information gained from this exercise will be vital for the structural engineer to decide the appropriate timber repairs and replacement works as necessary. Description The Resistograph is a drill resistance device based on the drill resistance measurement principle. According to this method, a thin corer needle (shaft diameter 1.5mm) rotates with approximately 1500 rotations/min and enters the wood with a constant advancement. The hardened tip has a special cut and has twice the breadth of the shaft (diameter 3mm) so that the substantial resistance falls on the tip of the needle. The strain on the motor, which rotates the corer needle as a result of the drill resistance or in other words its energy consumption, is then measured. The measurement accuracy can even detect the differences in the density of early and late wood. As a result, the drill canal is so fine that the drill shavings remain in the wood and almost no air can enter the wood, which minimises the decay infection. This device dispenses with the high resolution representation of the wooden structures and detects small internal defects to severe decay. Resistograph E400, the measurements results are printed out on site with the aid of a computer and the printout in a scale of 1:1. The printout gives the information, which can be interpreted as: Beginning of examination, Healthy, Side infected by decay, Crack Rotten decay, Severe decay, depending upon the timber tested. Timber Stress Grading and Species Identification EBS offers stress grading and identification of timber species and identification and viability of decay organisms for example fungi and insects as necessary. It is important to identify the timbers for visual stress grading and the decay organisms. The information gained from stress grading exercise will be vital for the structural engineer to decide the appropriate timber repairs and replacement works as necessary. Moisture Distribution in the Masonry EBS can carry out moisture mapping for the residual moisture distribution in the masonry. If the masonry is found to be wet, then appropriate recommendations can be put in place as deemed necessary to encourage drying of the fabric. Timber Moisture Contents EBS can carry out moisture monitoring of the structural timbers. If the timber members were found to be wet, then appropriate recommendations can be put in place as deemed necessary to encourage drying. |
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