Profile Boards Placement
What is a building profile board?
A building ‘profile boards’ is a board used to transfer the plan outline of a building onto the ground. Profile boards are held securely in one place and are made level and parallel to the floor. see figure below.
Establishment Of Excavation Width And Wall Thickness On The Profile Boards
The figure above shows a continuous profile board.
The width of the foundation trench to be excavated is thrice the wall thickness (standard). But this can be modified in order to avoid concrete wastage during foundation blinding or casting. In the case of the figure above, the wall thickness is 230mm.
Going by the standard; the excavation width will be 230×3= 690mm which is not economical in terms of excavation cost and concrete usage. Hence, we modified it by creating a clearance of 150mm on both sides of the wall thickness for easy working in the foundation trench by the mason during block laying in the foundation trench.
This now give us 150mm+230mm+150mm=530mm. hence, from the already established lines AB, AG, BH, and GH which are the outer lines of the outer walls of the building, 150mm will be measured outward (cd=150 mm) and marked with nails fixed to those points while the 230mm and 150mm (bc=2300 mm and ab=1500 mm) will be measured inward on the profile board as shown in the figure above. therefore, the foundation width is now (ad) where (bc) represent the wall thickness.
Excavation Of Trenches
After marking out the foundation and wall width, lines are used to align the respective points of opposite sides as marked out on the profile board. After which, excavation exercise will be carried out. The width of the excavation is guided by the lines as shown the figure above. see trench excavation diagramme below