In-situ micro-rheology – a method for the study of skin and crust formation at mortar surfaces (Part 1)

Once a mortar is applied as a thin layer to the substrate, the mortar surface is exposed to the environment and changes its properties over time. In the case of a tile adhesive, the surface of the applied mortar readily starts to form a thin skin (< 0.1 mm), which can continuously thicken to form a dry crust with a thickness of 0.5-1.0 mm within 30 minutes of exposure time. Such a crust is a barrier between the fresh mortar underneath and the tile above and prevents a proper wetting between the two materials. As a result, the adhesion strength is reduced, as can be measured by the open time test (EN 1346). This paper presents a new rheological in-situ method for the measurement of the crust build-up during the first 30 minutes with a spatial resolution of one micron. First measurements indicate two principal types of mortars. Some of which form a crust and others thicken homogeneously throughout the entire mortar layer. The method can be applied to any soft material with a viscosity gradient perpendicular to its surface.

1 Introduction

In the case of a tile adhesive mortar, the open time is the maximum exposure time of the applied mortar layer (combed with a toothed trowel onto a wall or a floor) until the tile is embedded, without losing the performance of adhesion.

The European Standard EN 1346 (note that in 2017 EN 1346 was included in EN 12004) defines how open time of a tile adhesive is measured quantitatively under laboratory conditions. The freshly mixed mortar is applied with a 6 mm x 6 mm x 6 mm toothed trowel onto a standardized concrete substrate. After 5, 10, 20 and 30 minutes, 5 cm x 5 cm,...

Related articles:


Skin and crust formation at mortar surfaces – mechanisms and influencing factors (Part 2)

1 Introduction Mortars are applied in relatively thin layers, which are exposed to substrate and air. Thus, environmental parameters have a strong influence onto the development of an applied mortar...

Issue 2021-7 LPM AG

Extended Open Time – the need for standardization of an important characteristic of tile adhesives

1 Background situation Adhesives for ceramic tiles are standardized by the EN 12004, which is subdivided into two parts. Part 1 contains the requirements, assessment and verification of constancy of...

Issue 2011-11

Adhesion between tile adhesive and modified rear sides of porcelain tiles

Experiments were conducted on the quality of the bonding achieved by tile adhesives with various pre-treated rear sides of tiles. Conclusions drawn from the results point to ways of improving the...

Issue Drymix 2015 AKZO NOBEL

Buttering to be on the safe side – six material technology advantages of buttering

1 Introduction Two very different material surfaces come into contact when a porcelain tile is placed by the floating method. On one side there is the previously combed mortar that forms a thin dry...

Issue Drymix 2015 ASHLAND

Culminal™ Plus for additional ­security in premium cementitious tile adhesives

Culminal Plus is a new series of modified methylcelluloses for use in premium cementitious tile adhesives. Cementitious tile adhesives are clearly specified in EN 12004/ISO 13007 as to their...