How to Determine Coating Porosity Using the Buoyancy Method

       (1) Peel off the coating from the substrate, and there should be no obvious unevenness in appearance.



      (2) Dry the coated test piece in the air at 105°C to 120°C for about 2 hours to make the mass constant, and weigh out the mass m1 of the dry test piece.

      (3) Immerse the dried test piece in distilled water at room temperature, soak and exhaust under vacuum, take out and weigh after recording the bubbles, and this test piece is called a saturated water test piece. Then use a thin metal wire with a diameter of 0.5 mm or less to suspend the saturated water sample in water and weigh it, and the weighing value after deducting the weight of the wire is taken as the water mass m2 of the saturated water sample.

      (4) Take the saturated water sample out of the water, quickly dry it with a damp cloth and weigh it, as the mass m3 of the saturated water sample. Then the surface porosity can be calculated by the following formula:

         Apparent porosity (open porosity) ε = (m3-m1)/(m3-m2)x100%