Views:217 Author:Site Editor Publish Time: 2017-03-22 Origin:Site
MAGNESIUM-OXIDE BOARDS CAUSE MOISTURE DAMAGE INSIDE FACADES IN NEW DANISH BUILDINGS
Kurt Kielsgaard Hansen (1), Tommy Bunch-Nielsen (2), Bent Grelk (1), Carsten Rode (1)
(1) Technical University of Denmark, Lyngby, Denmark
(2) Bunch Building Physics ApS, Vedbæk, Denmark
Magnesium oxide board, “MgO-board”, is a factory-made sheathing board product, which has been widely used in the last 5 years in ventilated facades on new or renovated buildings in Denmark. In winter 2014/15, a number of problems began to appear with these boards since the boards and adjoining building elements seemed to suffer from some sort of disease, which manifested itself by damages such as significant moisture, boards leaking salty water (‘tears’), corrosion of fittings and anchors and mould growth.
The damages were caused by the fact that MgO-boards absorb moisture from outside air in periods with high outdoor humidity (90-100% RH) and form water drops on the surfaces. The drops contain a high amount of soluble chloride ions and appear on the surfaces of the boards and may often run down the boards and to adjacent structures. Metal fixtures for the MgO- and siding boards may corrode heavily within a few years. The binder in MgO-boards is formed by chemical reaction between MgO and MgCl2, known as magnesium oxychloride cement or Sorel cement. Also organic matter can be found in the material. The paper presents results of investigations of properties for moisture retention and transport of MgO-boards.
In winter 2014/15, many moisture damages were observed inside ventilated facades of new or newly renovated Danish buildings. The moisture damaged facades were constructed with sheathing made of magnesium oxide-boards (MgO-boards) facing the air gap behind the ma-terial used for exterior siding. MgO-boards have often been used as sheathing behind a venti-lated air gap as shown in Figure 1 and Figure 3. A photo of a MgO-board is shown in Figure
International RILEM Conference on Materials, Systems and Structures in Civil Engineering
Conference segment on Moisture in Materials and Structures
22-24 August 2016, Technical University of Denmark, Lyngby, Denmark
Figure 1: Sketch of a typical façade con-struction where a sheathing board is used as wind barrier. Adapted from .
Figure 2: Photo of 8 mm thick MgO-board with a glass fibre mesh on both surfaces.
The observed damages were caused by the fact that MgO-boards absorb moisture from out-side air. Water drops containing chloride ions appear on the outside of the boards – often so many that they run down the vertical boards and out via the air gap behind the siding boards (see Figures 4 and 5). The metal mountings for the MgO-boards can corrode heavily within a few years, cf. Figure 6.
Figure 3: The MgO-board is placed facing the air gap, which is behind the siding boards made of natural slates.
Figure 4: Salty water drops on a vertical MgO-board on the side that faces the nsula-tion filled cavity inside the wall.
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