Testing the chemical resistance of waterproofing and protective membranes - Part 2

Part 2 / 3: Five test methods to?evaluate chemical resistance

Following Part 1 of this blog, Is this membrane resistant to sulfonistic acid? this article gives an overview of five different methods for the assessment of the chemical resistance of waterproofing membranes and protective coatings, and the differences in the procedures, to highlight the influence of the method on the results obtained.

1. Internal ad-hoc methods

Tests carried out following procedures developed by the manufacturer itself and evaluated according to its own criteria. The information provided by these tests can be very useful but does not allow products from different suppliers to be compared, as the test does not conform to a common methodology.

2. ASTM D 1308: Effect of Household Chemicals on Clear and Pigmented Organic Finishes.

This procedure was developed to evaluate the effect of chemicals like ethyl alcohol, vinegar, soap solutions, fruits or other substances used in most homes, using two possible contact methods to simulate exposure of the coating to possible spills: a “spot test” and “immersion”. Other chemicals can also be used if agreed between parts.

There is no weathering specified in the testing procedure and the contact of each chemical with the membrane takes place over seven days at room temperature and without applying pressure (unless otherwise specified). The samples are inspected daily for surface alterations such as discolouration, change of gloss, blistering, softening, swelling, loss of adhesion or any other changes which must be reported.

3. ASTM D 3912: Standard Test Method for Chemical Resistance of Coatings and Linings for Use in Nuclear Power Plants

This test method describes the immersion method of exposure to chemicals for coating systems used on the surfaces of tanks, vessels and similar facilities in nuclear power plants.

As in the previous case, there is no weathering specified before the coated panels are immersed halfway into individual chemicals for a period of 5 days (short term) or 180 days (long term) at 25oC. After the exposure, the samples are evaluated to detect signs of delamination, blistering, discolouration, softening or other effects.

4. ASTM D 6943: Immersion Testing of industrial protective coatings and linings

This test establishes procedures to evaluate how protective coatings resist degradation by chemicals and how they protect the substrates from corrosion as a result of contact with the fluid. It also evaluates how coatings protect the contents of a vessel from contamination with particles coming from the substrate or from the coating itself.

Tests proceed with immersion in chemicals under three possible exposure conditions: at constant temperature (+23oC) and atmospheric pressure, with gradient temperature and at constant temperature (+43oC) and 3 bars of pressure.

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5. EN 13529 Products and systems for the protection and repair of concrete structures - Test methods - Resistance to severe chemical attack

Similar to ASTM D 6943, this European Standard specifies a method for determining the resistance of surface protection systems to severe chemical attack by exposing one side of the coating or membrane to the testing liquid.

The standard suggests a list of 20 testing liquids that represent a whole class of substances with similar chemical behaviour. The duration of the test is typically 1, 3, 7, 28 or 90 days. Two optional conditions can be added to the test: a 1 bar pressure applied on the testing chemical or the protection system bridging a crack opened in the concrete substrate.

As in other tests, after being subjected to a chemical attack the samples are inspected in comparison to an unexposed one for blistering, flaking, cracking, optical changes, adhesion, hardness and penetration of the testing liquid through the coating. All changes and variations must be reported.

With the results of the test, the EN 1504 part 2 “Products and systems for the protection and repair of concrete structures. Part 2: Surface protection systems for concrete.” specifies a maximum reduction of 50% of original hardness when measured according to Buchholz or Shore methods, and classifies the chemical resistance of the protection system in three levels:

• Class I: 3 days exposure without pressure.
• Class II: 28 days exposure without pressure.
• Class III: 28 days exposure with pressure.

As we saw in Part 1 of this series, there is no simple answer to the question of whether a membrane is resistant to a chemical. It is necessary to select the testing method that best simulates the real exposure conditions.

In Part 3 of this entry, I will describe what is possibly the most comprehensive technique for testing the chemical resistance of a coating or membrane exposed to industrial conditions.