How to putty a wall with a grater?
| Applying a key to a wall involves scratching it to prepare the surface for the next coat of plaster. If there are three layers of plaster, the second will need to be puttied. This process increases the surface area and means the plaster is pushed into the gap or hole so that it can be "captured" and locked (like a key) more effectively. | |
| Many plasterers use the devil's grater to secure the wall. This is a piece of wood with screws or nails driven into the butt. The screws must not protrude from the base by more than 1 or 2 mm, otherwise the scratches will be too deep and will still be visible through the last layer. |
 | Wait until the plaster hardens enough. You will know it is ready when the surface is still slightly spongy but not yet hardened. Carefully drag the devil's bobber across the figure-eight surface. Move up and down the length of the wall until it is completely covered. Try to keep the gap between scratches no more than 150 mm (6 inches) and be careful not to push the float too hard. |
 | After application, wait approximately 20 minutes, then lightly run a clean plastic trowel over the wall. This will even out the surface and get rid of any large burrs that may have formed during the scratching process. |
 | You can also use a scratching post or a scarifier to clear the wall. For more information, see the Wonkee Donkee guide: Plaster claws. |
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