One of the first and most important techniques that a plasterer should be taught is the importance and necessity of forming screeds using the dot and screed method.
Open up any plastering book from the last 200 years and the method should be explained in the first chapter, although many modern plasterers seem to think it is an old, unused practice there is in my opinion no better way of establishing a truly square and plumb job. This should be one of the first processes carried out before any moulding or rendering is completed.
The restoration project we are working on has a lot of in situ mouldings and to achieve the required end result we had to prepare and plumb the building using this method.
Brief explanation (there are various ways this can be done however in this instance this is how we did it)
- Hammer a masonry or clout nail into brickwork a few inches in from either end of the wall. Leave the nail head sticking out a little (1/4″ or so)
- Pull a string line between these two nails and insert further nails along this line, spaced out at a distance a little less than your straight edge.
- With the string line pulled tight off the heads of the two end nails hammer the intermediate nails in until the heads are lined up to the same depth as the string line
- We added a second top screed by hammering a row of nails above these and using a small level to set the depth
- Apply dots of material on and around all of these nails and after a short while rub up these dots with a float until the nail head begins to show
- When the dots feel firm apply a continuous band of material between the dots and rule off with a straight edge using the dots as a guide.
- Allow the formed screeds to set a little then fill in any imperfections and rub up entire screed with a float to a smooth finish.
- Close in with a plastic or steel trowel if required
Ideally we would have liked to have carried out all of the scratch coat and rendering on this job ourselves, after the mouldings were in place, but this had been carried out before our arrival on site so we have to remove and replace some layers of material in order to complete our moulding works.