How to Test Water Vapor Barrier Property of Latex Paint

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Latex paint is one common organic paint that is used in construction industry, which is also known as acrylic paint. There are mainly two types of paint on the market, acrylic paint and oil-based paint. Acrylic latex paint is made with water and an acrylic resin binder. All paints are composed of a solid, binders and pigments and a vehicle such as water for latex paint.

After latex paint is applied to a wall, it remains flexible, meaning that as the temperature changes, the surface will expand or contract. Latex paint is also porous and allows moisture to escape from the paint surface. Latex paints do not cause cracking and peeling as do oil based paints. But if the water vapor barrier property of latex paint is poor, the moisture in the drywall can escape through the porous surface of the paint, those problems mentioned above may occur to the surface of the paint. Therefore, it is necessary to examine the water vapor barrier property of latex paint before use.

This article provides a test method of water vapor permeability of latex paint for your reference. We tested one brand latex paint with Labthink’s W3/062 Water Vapor Transmission Rate Test System.

Figure 1. Latex Paint

Currently, there are mainly two categories of test methods for water vapor transmission rate i.e. gravimetric method (also known as cup method and divided into dry cup method and wet cup method) and sensor method (including electrolytic sensor method, infrared sensor method and humidity sensor method). Labthink’s W3/062 Water Vapor Transmission Rate Test System uses gravimetric method. In the tests, the specimens are clamped in test dishes and under a certain test temperature, a constant humidity difference is generated between two sides of the test specimen. The water vapor permeates through the specimen and into the dry side. By measuring the weight changes of the test dish in different time, water vapor transmission rate and other parameters can be obtained. The humidity of the test chamber for water method is lower, while the humidity of the test chamber for desiccant method is higher.

Figure 2. W3/062 Water Vapor Transmission Rate Test System

The tests are performed according to the following procedures.

(1)   Cut three pieces of specimens from the sheet made by provided sample of latex paint. The diameter of the specimens should be 74mm.

(2)   Add some dry anhydrous calcium chloride in the test dishes, which will be used as desiccant.

(3)   Clamp those three specimens in the test dishes respectively.

(4)   Place those test dishes on the dish supports inside the instrument. Then close the door of the instrument.

(5)   Set specimen thickness, test temperature, humidity and other parameters. Then click Start Test to start the tests.

(6)   The instrument will weigh the test dishes according to the preset settings and finally calculate and display the test results automatically.

For more details about W3/062 Water Vapor Transmission Rate Test System, please visit www.labthink.com

About Labthink Instruments Co., Ltd:

Labthink Instruments Co., Ltd is one leading supplier of packaging testing instruments, which is headquartered in Jinan, China and operated in Boston, U.S.A.