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Bond Strength of Adhesive Mortars to Substrates in ETICS-Comparison of Testing Methods
Paweł Gaciek1,2, Mariusz Gaczek3, Paweł Krause1
1Faculty of Civil Engineering, Silesian University of Technology, 44-100 Gliwice, Poland.
Materials (Basel, Switzerland)
|November 13, 2025
Summary
Adhesive bond strength in External Thermal Insulation Composite Systems (ETICS) is significantly reduced by thicker adhesive layers and vertical application, contrary to common guidelines. Realistic testing reveals critical performance variations impacting building safety.
Area of Science:
- Construction Materials Science
- Building Physics
- Adhesion Science
Background:
- External Thermal Insulation Composite Systems (ETICS) rely on adhesive mortars for bonding insulation boards.
- Current guidelines often recommend thinner adhesive layers than those used in real-world applications.
- Variability in application thickness and orientation can impact system performance and durability.
Purpose of the Study:
- To investigate the bond strength of cement-based adhesive mortars for expanded polystyrene (EPS) in ETICS.
- To evaluate the influence of adhesive layer thickness, substrate type, and orientation on bond strength.
- To compare standardized testing methods with a novel approach simulating practical application conditions.
Main Methods:
- Conducted field surveys and contractor interviews (170 questionnaires) to determine typical adhesive layer thicknesses.
- Performed laboratory pull-off tests using both standardized (EAD) and an in-house method.
- Varied substrate types (concrete, silicate), orientation (horizontal, vertical), and adhesive layer thickness (10 mm, 20 mm).
Main Results:
- Increased adhesive thickness from 10 mm to 20 mm reduced bond strength by 65-75% on concrete.
- Vertical orientation halved adhesion compared to horizontal placement on concrete.
- Silicate substrates showed lower but more variable bond strength; some failures occurred during preparation.
- Combined effects of increased thickness and vertical orientation drastically reduced adhesion on concrete (approx. 85%).
Conclusions:
- Adhesive layer thickness has a greater impact on bond strength than orientation.
- Substrate properties significantly influence mortar performance and variability.
- Current testing methods may not accurately reflect real-world performance due to differing application conditions.
- The developed in-house testing method provides a more realistic assessment of adhesive mortars under practical ETICS application scenarios.
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