- First work out what the minimum thickness of the screed bed needs to be.
- Next check that the base slab is level by using a laser level. If the slab IS level, skip the next step.
- If the slab is not level, use a laser level to find the difference in height of the drainage outlet and the floor at each perimeter wall.
- Measure the distance from the outlet to the furthest wall.
- Work out what fall you are trying to achieve. 1:100 is the minimum required by AS 3740 for bathroom floors outside the shower, and 1:100 is also required by AS 4654.2 for external balcony decks.
- Use the following formula to calculate the height of the finished floor level (H) at the walls. Once calculated, measure up the wall and mark the height.

H = L x r – d + s + t

where

H = height
of finished floor level at walls

L = length distance from outlet to wall.

r = ratio required to be achieved

d = difference in height of slab at wall relative to at outlet.

s = minimum thickness of screed bed

t = thickness of tile & adhesive

Example as follows:

Let’s say the distance from outlet to wall is 6 m, convert this to mm, L = 6000
mm.

r = 1:100

Let’s say the base slab at the wall is 5 mm lower than at the drainage outlet,
as determined used a laser level so d = -5

s = 60 mm

t = 8 mm

H = (6000) x (1/100) – (-5) + 60 + 8

H = 133 mm