A datum point is a point of reference which you can then measure from. The datum point is a reference point. This is used in forming levels so that all the levels are measured from a fixed point. The datum point can be placed on a wall or any given point and the plaster can transfer it around the site. All levels will be made from this point.
Another way of forming levels is to take the level from the bottom of a stair case or door frames. This is generally only done in domestic houses.
Using a brush, grout is applied to the place where the first narrow screed will be.
The first screeds should be just a little bit wider than the trowel and the grout should still be wet when applied. A flooring rule is then used to rule in the screed.
The accuracy of the screed is then checked using a builders square on the chalk line around the room.
Another way to level screed is to work from the bottom of a door frame. The screed is laid as normal, and then a level is placed on the flooring rule to check accurately how level the screed is.