Stage 5 – Placing in position the 4-inch PVC columns
In Stage 5 we place the thirty-two 4-inch PVC pipes (Photo 54) in the 60 cm deep pits previously dug (Photo 54). Placing the columns in the pits requires special attention both to alignment and height (Photos 55 and 56). Vertical straightness is achieved with a plumb line, while the baseline is placed 15 cm above the surface of the block/brick base (Photo 57). To ensure the exact height for each PVC column, it is advisable to mark 1.15 meter, from the bottom up, on all columns. To ensure that all the columns will have the same height, consider 60 cm in the pit, plus 40 cm of the brick/block height, and then mark another 15 cm, adding up to 1.15 meter. The line running 15 cm above the surface of the block/bricks foundation (Photo 57) will serve as reference for positioning and leveling the greenhouse columns (Photo 58). All the PVC columns are to be placed inside the block/brick foundation (Photo 59).
Observations: This process was utilized by a mason to build this particular CITIES WITHOUT HUNGER Agricultural Greenhouse; however, there are simpler methods to align and level the columns, so each person should adopt their own criteria for their agricultural greenhouse.
To ensure the 4-inch PVC columns are firmly in place it is necessary to pour the mortar into the pits (suggested measures are two 18-liter cans of sand, plus two 18-liter cans of gravel or gravel powder, plus 50 kilos of cement) with the column already in place and checked for straightness and alignment, as explained above. Pouring the mortar in the pit requires attention to keep column from moving (Photos 60, 61, 62 and 63) and ensuring the required straightness (Photos 64 and 65).
The next step is to place wooden baseboards along the block/brick base where the column was placed in order to fill in the gap between the concrete base and the column (Photos 66, 67 and 68).
After all the columns have been placed in the holes (Photo 69), it is advisable to allow two days before handling the structure to ensure the mortar is dry and the columns are firmly in place.