Wetting bales
The bales must be wet, though not dripping, prior to applying the plaster or the straw will quickly draw the moisture from the plaster, resulting in extensive cracking and a weak application.Plaster
Introduction
The bale walls in this structure were plastered with natural hydraulic lime, or NHL. Mined and processed in Europe, this product is additive free, resists insects and rodents due to its high alkalinity, and is relatively low in embodied energy when compared to cement-based plasters (about one quarter of that required to produce portland cement).
Troweling the plaster scratch coat just after spraying it onto the bales.
NHL also is somewhat elastic, allowing for minor movement without cracking. Due to the properties of NHL, should it crack it has the ability to heal itself to some extent. This is due to its absorption of CO2 during the ongoing carbonation process, which combines with free lime (CaOH2, or calcium hydroxide) in the plaster producing CaCO3 (calcium carbonate), or, natural hydraulic lime!
When using NHL it is desirable, though not required, to allow the maximum time possible (though no less than two weeks) between applications; even months! This permits any cracking that might occur to be inspected, and, if required, to be corrected prior to the next coat. This prevents the crack from telescoping through the subsequent coats and creating a moisture conduit into the bales. Minor cracking will occur and is not a problem. This process addresses any larger cracks, should they occur.
1 l more to come...