Most modern bridge decks are waterproofed in spray-applied polymeric coatings. Once asphalt has been applied to it, however, the two are inextricably bonded together, so any defects in the waterproofing cannot be rectified. Whilst it is possible to test the waterproofing with the asphalt in-situ, this can only provide approximate locations to defects, the action of removing the asphalt is likely to damage the membrane further, thus negating the effects of test.
For this reason, it is considered essential that the waterproofing is fully tested beforehand by means of a holiday test, which should preferably be undertaken by an independent authority, such as Thornton Consulting.
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