Quick Answer
Cracking in earthbag plaster can be addressed through a combination of reinforcement, joint placement, and careful plaster application. Regular maintenance and inspections can also help prevent further damage.
Understanding the Causes of Cracking
Cracking in earthbag plaster is often a result of settlement or shrinkage of the earthbags, movement of the barbed wire or rebar used for reinforcement, or poor plaster application techniques. In earthbag domes, cracking is more common due to the curved shape and tension in the plaster. To minimize cracking, it’s essential to place joints in the earthbags at strategic locations, such as above windows and doors, or where the plaster will change direction. These joints allow the plaster to move and flex without breaking.
Reinforcing the Plaster
To reinforce the plaster and prevent further cracking, you can apply a layer of mesh or a fiber-reinforced polymer (FRP) grid to the earthbags before applying the plaster. This provides additional strength and flexibility to the plaster, allowing it to withstand settlement and movement. For dome structures, it’s recommended to apply a minimum of 3-4 layers of plaster, with each layer being 1/4 inch thick, to achieve a smooth and crack-resistant surface. In straight wall structures, a single layer of 1/2 inch thick plaster is sufficient.
Repairing Cracks
When repairing cracks in earthbag plaster, it’s essential to clean the area thoroughly and apply a bonding agent to the crack before applying a patching compound. A patching compound made from a mixture of earth, sand, and a small amount of cement can be applied to the crack and smoothed out to match the surrounding plaster. For more extensive damage, it may be necessary to remove and reapply the plaster, taking care to reinforce the area with additional mesh or FRP grid.
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