Standard · Adhesion, cure and holidays
ASTM D4752
MEK solvent-rub test for the cure of inorganic zinc silicate primers.
A cloth soaked in methyl ethyl ketone (MEK) is rubbed back and forth over an inorganic (ethyl silicate) zinc primer for 50 double rubs. A film that softens, or transfers a lot of zinc to the cloth, is not yet cured. Organic coatings have their own rub test, ASTM D5402.
The rating
- 5: no effect on the surface and no zinc on the cloth.
- 4: a burnished area and a little zinc on the cloth.
- 3: some marring and a visible dent in the film.
- 2: heavy marring and an obvious dent.
- 1: a heavy dent, but no penetration to the steel.
- 0: rubbed through to the steel.
A 5 usually allows topcoating. Agree the rating needed with the coating maker and the specification before the test, not after it.
Why the weather matters
These primers cure by reacting with moisture in the air, so humidity and temperature set the pace. The FROSIO book gives more than 50 % RH as the need for cure. The same primers mud-crack when applied too thick.
3 practice items in the members area mention ASTM D4752 (CIP 1: 1 · CIP 2: 1 · FROSIO written: 1).
Related
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Also published openly: KTA-Tator: cure testing of inorganic zinc-rich primers.
This page describes the subject of ASTM D4752 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.