The function of thin-coat textured renders is to protect the external wall against the adverse effects of atmospheric conditions and decorate the façades. They can be applied directly on traditional plaster, but they can also be the finishing layer of thermal insulation systems. The properties of the renders and in consequence - their suitability, are determined mainly by the binder used to manufacture them.
Render selection criteria
It is necessary to have a good knowledge of the building to select the render properly. Here is a list of questions that have to be answered in order to make the best possible choice.
The render must not substantially limit the flow of water vapour through the partition. Before taking the decision, it is worth to ask Atlas advisors for help and they will carry out the calculations and design the partition correctly. If the renders are applied to walls made of high vapour-permeability materials, e.g. cellular concrete, they must have similar properties. In such case, mineral or silicate binder - based renders should be used. Similarly, when the wall is insulated with mineral wool.
For rendering decades old buildings, definitely vapour-permeable renders should be used, particularly silicate ones, because weathered walls have very high vapour permeability.
If yes, there is always a possibility of occurrence of organic contamination, fungi and algae on the façade. In such case, mineral or silicate renders are recommended, since they have strong alkaline reaction (pH ~12), making the development of microorganisms practically impossible. Dispersion renders contain addition of biocides limiting the development of microorganisms. Another favorable factor in fighting biological corrosion is their low absorbability, impeding sedimentation of spores.
If the answer is «yes», then silicone render is recommended, because it is the easiest to keep clean – smaller pollutions are removed by rain. Dispersion renders also don't yield to structural pollution and damaging them during washing is hardly probable.