Osmose - Theorie der Bildung von Blasen unter Beschichtungen / Osmosis - Theory of blister-formation under Coatings

The formation of blisters is a well-known phenomenon in coating of concrete and other mineral substrates. Especially, when dealing with wet or humid substrate, osmosis may occur. A semipermeable membrane is formed between a concrete coating and the concrete surface, followed by water transport, which results in fluid-filled blisters. In this report, the conditions necessary to promote osmosis are explained in detail. The type of concrete, the condition of its surface, the presence of osmosis-promoters and the type of coating are important factors which influencethe formation of blister. Evaluation of the literature and test results lead to a set of recommendations on how to avoid the formation of osmosis-caused blisters.