What defines a 'surface dry' condition in this standard?

A film is considered surface dry when ballotini (glass spheres) sprinkled on it can be lightly brushed away with a soft brush without damaging the paint surface.

How is the 'hard dry' condition verified?

It is typically verified when gentle but firm rubbing with a thumb does not mar, wrinkle, or detach the paint film from the substrate.

What are the standard ambient conditions for conducting these drying tests?

The tests should be conducted at a temperature of 27 ± 2°C and a relative humidity of 65 ± 5%.

IS 101 Part 3/Sec 1

: 1987

Methods of sampling and test for paints, varnishes and related products: Part 3 Mechanical tests for paint films Section 1 Drying time

CurrentSpecializedTesting MethodMaterials Science · Painting, Coatings and Surface Finishing

Archive.org BIS Portal Google

This section of IS 101 prescribes the standard methods to determine the drying time of paint and varnish films. It details the procedures for assessing different stages of drying, including 'surface dry', 'hard dry', and 'tack-free' conditions, which are critical for QA/QC testing and ensuring adequate curing before applying subsequent coats or handling.

Specifies methods for determining the drying time, surface dry time, and hard dry time of paint films.

Quick Reference Values

Standard Test Temperature27 ± 2 °C

Standard Relative Humidity65 ± 5 %

Mass of applied weight for hard dry testOften uses standard thumb pressure or specific weight depending on coating type

Practical Notes

Drying time is highly sensitive to ambient temperature, humidity, and airflow. Tests must be conducted strictly within the prescribed 27±2°C and 65±5% RH conditions unless specified otherwise.

The thickness of the applied wet film significantly impacts the drying time. Ensure uniform application using proper applicators to obtain reproducible results.

For the surface dry test, ensure the glass spheres (ballotini) are dry and free from contaminants before dropping them onto the paint film.