Insulating plaster: two options
Lime insulation is usually implemented in the form of a lime insulating plaster. Unfortunately, there are very few lime insulating plasters that can do without the addition of cement. The declaration of the ingredients is also often inadequate or misleading.
Nevertheless, there are two lime insulating plasters that are completely cement-free: the Hessler HP9 SL (SL stands for "Super light") and the Otterbein Calcea lime insulating plaster. There are two different versions of both products: interior and exterior plaster. Unfortunately, the external variant of a lime insulating plaster requires the addition of cement, as this is the only way to achieve the strength values that are necessary for an external plaster. So if you want a cement-free lime insulating plaster, you have to fall back on the variants for the inside, because the lime insulating plasters for the outside from Hessler and Otterbein also contain a small amount of white cement.
Layer by layer
With both plasters it is possible to vary the insulation thickness. Any number of layers can be plastered on top of each other. The thicker the layers, the longer the final drying and setting will take. It is not advisable to plaster more than 6 cm in one layer. The next layers should only be applied after drying. The two insulating plasters differ in some respects:
- Light aggregate: the Hessler HP9 SL contains expanded glass as a light aggregate, whereas the Otterbein Calcea contains a light mineral aggregate made of perlite. This has an impact on processing.
- Machinability: the mineral lightweight aggregate made of perlite is not very machine-compatible. Although the lime insulating plaster can be processed with the plastering machine, part of the lightweight aggregate is damaged and the range is reduced. This increases the density of the material and its insulation value decreases. Manual processing is recommended here. The expanded glass in the HP9 SL, on the other hand, is very pressure-resistant and stable and remains intact when using plastering machines, so that the insulation value actually achieved corresponds to the manufacturer's specifications.
Further processing: the Hessler Lime insulating plaster works as a single layer plaster and can be rubbed off the next day and then painted. The maximum achievable strength of the Otterbein Calcea lime insulating plaster is not that high, which is why further work steps are necessary. The manufacturer stipulates that a layer of Otterbein adhesive and reinforcement lime mortar with mesh should be applied as a finishing touch. This is followed by the fine-finish lime plaster that can be painted.
Lime insulating plaster for outside
In addition to these insulating materials, there exists also the hemp-lime, which can be used as a prefabricated building elements (masonry blocks) for a timber frame or as loose fill between ceiling joists or behind formwork.