Initial surface absorption
The initial surface absorption test (ISAT) uses a plastic cap sealed to the concrete surface using modelling clay. The cap has a water area of 5000 mm2. When working on a vertical surface the cap has to be kept firmly in position by bolting or some other means. To carry out the test, water is introduced into the cap via a connecting point and maintained at a head of 200 mm using a filter funnel. A second connection point to the cap leads to a horizontal capillary tube. The connection to the reservoir is closed and the absorption is measured by observing the movement of the end of the water line in the capillary tube during a fixed period.
The test method is covered by BS 1881-208 Testing concrete. Recommendations for the determination of the initial surface absorption of concrete.