NOURYON | INSTITUT FOR LIFE SCIENCE

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

1 Experimental setup for micro-rheology with a Krüss tensiometer K100 MK2 All authors
1 Experimental setup for micro-rheology with a Krüss tensiometer K100 MK2
All authors
2 Wetting capability of mortars seen through glass plates (10 cm x 10 cm). The plates were laid 10, 20 and 30 minutes after application of the adhesive mortars (upper row: “F-wall”, lower row: “F-floor”) according to EN 1347. The insets show corresponding skinning patterns (skin and hollows appear black; arrows indicate cracks in the skin which appear bright), which can be visualized by total reflectance of light which is directed from the side into the glass plate. Test setup is described by Zurbriggen et al. [7]
2 Wetting capability of mortars seen through glass plates (10 cm x 10 cm). The plates were laid 10, 20 and 30 minutes after application of the adhesive mortars (upper row: “F-wall”, lower row: “F-floor”) according to EN 1347. The insets show corresponding skinning patterns (skin and hollows appear black; arrows indicate cracks in the skin which appear bright), which can be visualized by total reflectance of light which is directed from the side into the glass plate. Test setup is described by Zurbriggen et al. [7]
3 Wetting percentage (modified EN1347) versus adhesion strength (EN1346) as a function of exposure time. (a) Laboratory wall and floor tile adhesive (“F-wall”, “F-floor”) in comparison to commercial products for wall and floor applications (“Com-wall”, “Com-floor”). (b) Influence of different ingredients (“F-ref”: reference mortar, “F-cem”: mortar with finer cement, “F-tar”: mortar with tartaric acid, “F-24”: mortar with more water) and application parameters (“F-10”: combed with 10 mm x 10 mm x 10 mm trowel, “5°/80%”: stored in a cold and humid climate)
3 Wetting percentage (modified EN1347) versus adhesion strength (EN1346) as a function of exposure time. (a) Laboratory wall and floor tile adhesive (“F-wall”, “F-floor”) in comparison to commercial products for wall and floor applications (“Com-wall”, “Com-floor”). (b) Influence of different ingredients (“F-ref”: reference mortar, “F-cem”: mortar with finer cement, “F-tar”: mortar with tartaric acid, “F-24”: mortar with more water) and application parameters (“F-10”: combed with 10 mm x 10 mm x 10 mm trowel, “5°/80%”: stored in a cold and humid climate)
4 A fresh cut across two mortar ribs about an hour after the mortar was troweled onto a non-porous ceramic plate. One can see a closed thin skin at the surface, thick porous crust underneath the skin and wet mortar in inner parts of the combed ribs
4 A fresh cut across two mortar ribs about an hour after the mortar was troweled onto a non-porous ceramic plate. One can see a closed thin skin at the surface, thick porous crust underneath the skin and wet mortar in inner parts of the combed ribs
5 (a) Wall tile adhesive and (b) floor tile adhesive with an open time of 21 and 27 minutes, respectively (Table 1). The region between 25 and 50 mN corresponds to the zone of real pressures (8-16 mN/mm2), which act on the mortar rib when a 5 cm x 5 cm tile is loaded with 2 kg. For the 60 min-curves the yield point (circle) and the point at 2 mm depth (quadrangle) are marked. For further explanations see text
5 (a) Wall tile adhesive and (b) floor tile adhesive with an open time of 21 and 27 minutes, respectively (Table 1). The region between 25 and 50 mN corresponds to the zone of real pressures (8-16 mN/mm2), which act on the mortar rib when a 5 cm x 5 cm tile is loaded with 2 kg. For the 60 min-curves the yield point (circle) and the point at 2 mm depth (quadrangle) are marked. For further explanations see text
6 Plot of strength at yield point versus strength at a depth of 2 mm. With this type of diagram the dynamics of crusting of a particular formulation can be followed in detail. For further explanations see text
6 Plot of strength at yield point versus strength at a
depth of 2 mm. With this type of diagram the dynamics of crusting of a particular formulation can be followed
in detail. For further explanations see text

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,...

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ZKG 5/2019

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ZKG 5/2019

Ressort:  Application
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TEXT R. Zurbriggen1, Th. Bühler2, L. Huwiler1, U. Pieles2
1Nouryon (former Akzo Nobel Chemicals AG, and Elotex AG), Sempach Station/Switzerland
2Institute for Life Science, University of Applied Sciences Northwestern Switzerland, Muttenz/Switzerland

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