How to use a plasterer’s scratcher

Scratchers, or scarifiers as they are alo called, are used in the under layers of plaster and rendering, primarily the first or scratch coat. 

They create a surface for the next layer of plaster to be keyed in to.

Keying in, is where the plaster is pushed into a gap or hole so that it can ‘grab’ more efficiently and lock (like a key). 

Step 1 – Hold scratcher

The scratcher or scarifier is held in your stronger hand

Step 2 – Drag scratcher across surface

After the first coat is applied, but still wet, the scratcher or scarifier is dragged across the wall either horizontally or diagonally.

Enough pressure should be applied to create visual indentations but not so deep as to reveal the backing material. 

Which pattern should you create?

The pattern you create is a personal choice, however the diagonal cross-hatch is advised when applying on top of wooden laths. This creates a better bond that is in a different direction to the laths. 

Using tape

Some people choose to apply tape to their flat pronged scarifier. This achieves a cleaner scratch and prevents deep indentations.

The tape is applied to leave around 6mm (¼”) of exposed prong.