Civil Engineering Reference
In-Depth Information
Wetting down hempcrete to ensure the correct level of suction (see
box overleaf) before applying a basecoat plaster.
Suction
Any surface on to which a wet finish is applied (the substrate) will have a certain
amount of 'suction', i.e. it will suck water out of the wet finish. Suction varies with differ-
ent types of substrate, and also with different levels of moisture content present in the
substrate.
This sucking action is a key factor in how the plaster adheres to the wall, and it is im-
portant to have control over it, since either too much or too little can cause problems
for the lime plasterer. Very high suction (from a dry substrate) can draw too much wa-
ter from the plaster and not leave enough to set it, causing the plaster to fail. Too little
suction (from an over-wet substrate) can result in the plaster not adhering to the back-
ground, and slumping or falling off the wall.
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