Testing Plaster Surfaces

What does the term "mineral dry mortar CS II according to DIN EN 998-1" mean in the tender?

What requirements does a coating material have to meet if the architect calls for “Gypsum plaster dry mortar B1 according to EN 13279-1”? Questions that make it clear that, in addition to the practical testing of mineral plaster substrates, there are other criteria to consider.

Current regulations in the area of national and European standardization are particularly worth mentioning. These play a central role in the offer, planning and advisory phase, because only in this way can limitations in the warranty be made known and technically correct justified if there are underground defects and concerns. Part 5 of the Malerblatt series for substrate testing therefore deals with current technical standards for mineral plastering mortar.

For newly created plaster surfaces (e.g. in new buildings), the manufacturer's information is usually available and can therefore be included in the assessment of the substrate. There is often no detailed technical information on the quality of an existing old plaster base to be tested. On site at the construction site, the evaluation of the appearance or the result of the underground test is therefore important. This includes the concrete name of the plaster mortar as well as the abbreviation assigned to it and the compressive strength. And to do this, you have to know what has changed in the area of standardization and what is relevant for performance descriptions and implementation documents. The manufacturers of painting and coating systems also include abbreviations and compressive strength information in their practice data sheets and processing recommendations,to clarify the suitability of your products for plaster substrates.

Valid standards

On the one hand, EN 998-1 “Specifications for mortar in masonry construction - Part 1: plastering mortar” should be mentioned here. It defines abbreviations for mineral finishing plasters, such as GP for normal plaster, LW for light plaster and T for thermal plaster. In addition, the properties of solid mortars are classified with the information compressive strength (CS), capillary water absorption (W) and an assessment of thermal conductivity (T).

DIN EN 13279-1 applies to gypsum binders and gypsum dry mortar: "Terms and requirements". This standard specifies types of plaster, their abbreviations and various requirements for gypsum dry mortar, such as the content of gypsum binder, start of stiffening, bending tensile and compressive strength, surface hardness, adhesive strength.

Use in practice

Since December 2014 and July 2015, the current two-part standard DIN 18550 "Planning, preparation and execution of interior and exterior plasters" has replaced DIN V 18550 (2005-04). It contains additional stipulations - in part 1 to DIN EN 13914-1 for exterior plasters and in part 2 to DIN EN 13914-2 for interior plasters - and addresses additional topics and problems, such as the classification and assessment of cracks, reinforcements with fabric inserts, Quality levels for interior plaster surfaces and clay plasters. For the execution and processing of plasters, some standards, both European and national, must currently be taken into account.

Which facade or interior paint can now be used professionally if the invitation to tender includes “mineral dry mortar CS II according to DIN EN 998-1” or “gypsum plaster dry mortar B1 according to EN 13279-1”? The answers to these questions can also be found in BFS Leaflets No. 9 and No. 10. What happens if the type of plaster and surface condition are not taken into account when planning and executing coating work is illustrated by the following practical examples.

A dispersion silicate paint or silicone resin paint would have been the suitable coating for the facade of the thermally insulated apartment building with mineral mineral scratch plaster CS I according to EN 998-1 with a possible compressive strength of 0.4 to 2.5 N / mm². Instead, the plaster surface was coated with a weather-resistant acrylic facade paint, also due to the desired color. Due to the low subsurface compressive strength, large stress differences arose between the coating and the plaster surface. The result is cracks and flaking. In addition, the higher proportion of lime in the plaster layer is also damaged in its substance by the carbonation-inhibiting effect of the plastic emulsion paint.

The next picture is a descriptive example of an inadequate surface condition or pretreatment: You can see a machine gypsum plaster (e.g. plaster plaster dry mortar B1 according to EN 13279-1) as a surface that did not meet the intended pressure resistance of 2 N / mm² and the surface of which is strongly chalking. The existing organically bound structural coating has cavities in some areas and detaches in the event of mechanical damage.

Conclusion

Plaster surfaces inside and outside are to be checked and assessed professionally and professionally. For this, the underground inspection on the construction site and knowledge of the currently applicable standards and guidelines is necessary. Only the two together create the ideal conditions for making the right decisions in planning, advice and practical implementation.

Johanna Westermeier

Photos: Brillux