Standard · Concrete
ASTM D4787
Continuity (holiday) testing of linings on concrete.
ASTM D4787 covers spark testing of new non-conductive linings on concrete, to find pinholes, voids, holidays and cracks. The current edition is D4787-24.
Why concrete is different
Steel conducts; concrete conducts only through its moisture, rebar and make-up. The inspector therefore first checks that the concrete, or a conductive primer laid under the lining, can carry the test current. The ground lead goes to rebar or another permanent metal ground, or to a wet sandbag on the concrete.
In practice
- Use a pulsed or continuous DC high-voltage tester at the voltage the standard's method gives for the thickness.
- Move the electrode at about 0.3 m/s (1 ft/s) and mark each indication for repair.
- Test only new linings: a lining that has been in immersion can be damaged by the spark or give false readings.
- Solvent left in a fresh lining can ignite. Test only when it has cured enough.
3 practice items in the members area mention ASTM D4787 (CIP 2: 3).
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This page describes the subject of ASTM D4787 in our own words; it does not reproduce the standard. For the full text, buy the current edition from ASTM International. Checked on 2026-10-14; errors go in the corrections log. CoatMentor is an independent study aid. It is not affiliated with ISO, AMPP, SSPC, NACE International, ASTM or FROSIO.