Formwork can be made from a wide variety of materials, as the load on shuttering is much less than for concrete work. Proprietary formwork and shuttering systems such as Geo-panel, plywood or PSB sheets are often used in hemp construction. Proprietary lightweight plastic systems such as those used for rammed earth construction may be useful in hemp construction. If reusable formwork is used the surface must be clean. Within the limits of the framework and formwork, curved walls can also be created.
The formwork can be removed from a cast wall the following day and any spacer holes filled with hemp masonry mix. It should be removed by sliding the sheets slightly sideways. Formwork should be removed at this time in order to encourage carbonation.
Once the frame of the building is completed either 600mm high internal and external formwork or shuttering is attached with spacers to the frame around the base of the house, or one side of the wall can be fully formed up. This should only be done where the build is continuous so the formwork will be removed within a few days. In this case, one side is fully formed up and 600mm sheets are attached to the other side. Additional 600mm sheets are added as needed.
In moderate weather no further protection of the drying wall is needed except against the extremes of the weather such as snow, frost, rain and drying winds. Using this method the shuttering or formwork is then attached to the frame higher up to build up the next 600mm of walling.
Permanent shuttering using a sheeting board can also be used to form the final finish of the wall. Where home owners choose to finish the home with timber cladding externally or internally, the use of a breathable membrane between the hemp masonry and the timber is recommended. This ensures that the movement of air, or breathability of the walls is maintained.
The sheeting board should be of a breathable, vapour permeable material. The use of particleboards and plywood is not recommended as permanent shuttering as these contain glues and may have limited breathability