Hydrated vs. Hydraulic
Hydrated lime, such as Type S or N, sets only via carbonation, that is, the absorption of C02. This greatly limits its thickness. Hydraulic lime, on the other hand, sets initially with water, like cement, and then continues to cure via carbonation.Plaster, p6
Brown Coat
As the banner states, this project is an experiment in straw bale construction, so we opted to apply the brown coat with a trowel, as opposed to using the sprayer, simply to compare and contrast the two methods. We found that trowelling requires less masking, but more time and physical effort in applying. It also tends to be less messy. Though equipment intensive, spraying is much faster and less laborious.
The brown coat being applied over the scratch coat.
The brown coat was mixed to a 1:2.5 ratio and applied to water-saturated walls to a thickness of about 1/2 inch. As the plaster firms up in the wheelbarrow, unlike cement, it becomes much more workable and adheres well to the walls. Plastering the rounded corners of the doors and windows was a bit tedious for a novice like myself, as the plaster would slough off if even slightly provoked. After a few hours of curing, though, the plaster could be worked to the desired finish with little chance of falling. An advantage to using NHL (natural hydraulic lime) is that, with a little misting, the plaster may continue to be worked, if required, even a day or so later.