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Step 5. PREPARATION OF THE BOTTOM SURFACE OF THE EXCAVATION
The preparation of the excavation bottom is critical so
the spa will fit properly. Thorough preparation will eliminate
settling, stress cracks and a minimum of time will be spent
setting the spa.
First, install the 2" x 4" screed rails length wise on
both sides of the excavation, using wood or metal stakes (Fig
3). Make sure the diagonal measurement is exact to insure
that the bottom is square. Adjust the Master screed to the
appropriate height using a transit level (see Fig 2). Second,
install the two Secondary screed rails on either side of the
Master screed using the offset dimensions as shown in Figure
3 and making sure that they are perfectly level to the Master
screed to insure that the bottom is square. Next, spread a layer
of sand approximately 4" deep evenly over the bottom of the
excavation. Rake the sand flat to the top of the screed rails (Fig
3). Compaction of the sand is achieved by the use of water and
walking over the entire bottom using your body for weight.
Rake and compact the area several times. Screed the bottom of
the excavation, filling any low spots as you go. The completed
area will resemble a slab of finished concrete. Remove the
screed rails and fill in the voids with sand, being careful not to
disturb the sand.
Figure 3
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