Drying out and building in winter
Following plastering a good cross-ventilation is to
be ensured so that the moisture can escape unhindered. With this the building
moisture is to be taken into account, which can possibly be increased still
further through the following situations.
In order that, in winter, a working-oriented temperature is ensured also at the surface of the construction item, the rooms should be heated and thoroughly ventilated for at least 3 to 4 weeks before plastering. With concrete as rendering base, as a rule at least 60 frost-free days are to be waited after removal of shuttering, unless the moisture of the concrete has verifiably reduced earlier to a percentage by weight of a maximum of 3.0 % (test using, for example a CM equipment).
Formation of sinter skin and gypsum plaster surfaces
If ventilation and removal of the saturated air is
prevented the transport of moisture within the plaster layer up to the surface
of the plaster is slowed down and thus the rate of drying of the complete
plaster layer is reduced. The result: the calcium hydroxide contained in the
gypsum plaster is dissolved and settles on the surface of the plaster. There it
reacts with the carbon dioxide in the room air to corm calcite. In the further
process it forms such a dense moisture impermeable layer, the so-called sinter
skin, which prevents the drying process.
A existing sinter skin can be identified easily by means of a wetting test. If the water is not taken up by the plaster layer but immediately pearls off – sometimes also only partially – this is a certain notice of a sinter skin which should be removed immediately.