Investigation of test methods for determining the resistance of mortars to frost and salt frost attack

11ntroduction Testing the resistance of concrete to frost and salt frost attack is a high-profile research subject [1] because of the mass usage of this construction material. The corresponding test methods are regulated in relevant standards. Mortars are used in significantly smaller quantities and also only a certain proportion of these material mixes requires a high frost or salt frost resistance. No direct method for testing these requirements has been standardized in Germany. For plastering mortar as per DIN EN 998-1 [2] the freeze-Thaw resistance of single-coat plastering mortar only has to be assessed indirectly by testing the adhesive tensile strength and water impermeability. For all other plastering mortars it holds true that u... the freeze-Thaw resistance has to be assessed and stated in accordance with the regulations that apply at the intended place of application of the mortarH. Nor does DIN EN 998-2 [3] for masonry mortar form a normative basis for a direct test method. Instructions for the avoidance of frost damage to mortar are given in Appendix B, in which it states that The ambient conditions to which the mortar is exposed should be borne in mind before selection of the mortar. This includes protection against water saturation.... The influence of a possible surface coating (e.g. paint) should be checked. Examples are also given of buildings at risk, but no specific instructions are given for carrying out a test. However, a comparative method is desirable for special applications, such as external renderings in splash water zones and external joints. At present the products from various dry premix mortar producers are stated to be frost resistant without any information about the test method. Different methods were applied and compared in two student theses (4, 5] at Bauhaus Univer- sitat Weimar to identify suitable and practical test methods with reproducible results. Initial conclusions about the basic viability of existing methods can be drawn from the results of the investigations. However, further research is needed to adapt them to the different types of stresses to which mortars are exposed.