Masonry Magazine May 1967 Page. 32
MATERIALS
Concrete block conforming to ASTM C90-64T for load-bearing foundation-wall units (Grade P or Grade U) should be utilized. Two-core block are recommended over three-core block only because the larger cores facilitate placing of reinforcing and grout. Reinforcement-Steel should conform to ASTM specifications for deformed bars or mesh, and be clean and rust free. Mortar and Cell Fill-Mortar and grout should be mixed in accordance with Table I, with the maximum amount of water which will produce good working or pouring consistency without segregation. Concrete should have sufficient water to produce a six-inch slump. Air entrainment for core-fill flowability is recommended. Minimum compressive strength for core-fill is 2500 psi at 28 days.
EXCAVATION AND FOOTINGS
Excavation to the staked lines and grades is normally done by a specialist with the proper equipment. Even hardened "do-it-yourselfers" agree that the modest cost of a professional who can ordinarily complete the project in a single day is well spent. Remember that it should be most economical and satisfactory to balance the excavation so the material removed can be used to build the sloping berm around the pool. This eliminates the necessity of hauling it away. The footing should be of poured concrete, as detailed in Fig 3. Place the required reinforcement accurately before the concrete hardens. The drain tile shown extends completely around the perimeter of the footing above its toe, and across the pool at its deepest point. Additional cross lines should be provided in larger pools. Connect this drain-tile line to a disposal means other than that used for the pool main drain. This eliminates the possibility of pool water backing up and saturating the subgrade.
MASONRY CONSTRUCTION
Swimming pool walls should be kept to a minimum height, because pressure against the walls increases exponentially with water depth. Increased depths for diving are attained by forming hopper-shaped bottoms (see Fig. 2). Block is laid by building the corners first and
Table I Mortar & Cellfill Proportions by Volume
| MIX | PORTLAND CEMENT | MASONRY CEMENT | HYDRATED LIME | DAMP LOOSE SAND | GRAVEL (MAX.) |
| :----------------------- | :---------------- | :--------------- | :-------------- | :---------------- | :------------ |
| MOTAR (Type S) | 1 Sack | 0 | 34 to 3½ Sack | 3% to 4 cu. ft. | 0 |
| Alternate Mortar | ½ Sack | 1 Sack (Type II) | 0 | 3% to 4 cu. ft. | 0 |
| Grout | 1 Sack | 0 | 0-1/6 cu. ft. | 295 to 3 cu. ft. | 0 |
| Alternate Concrete Cellfill | 1 Sack | 0 | 0 | 2½ cu. ft. | 2 cu. ft. |
+1 SACK 1 cubic foot
working towards the center, with each block levelled end-to-end and side-to-side and aligned along a string. The first course of block on the footing is laid in a full mortar bed, with only face-shell bedding for the higher courses. Horizontal reinforcing steel is placed as the wall rises. The first lift of grout or concrete core-fill is placed and tamped after the walls have reached a height of three to four feet. Stop the core-fill below the top of a course so that a continuous plane of weakness through the wall is not formed. After an hour's wait, the core-fill is again rodded or compacted, and masonry construction continues.
During wall construction, provisions are made for the underwater lights, surface skimmer, and fittings and accessories previously selected. Expansion or contraction joints are unnecessary in walls less than 50 feet and are actually undesirable as possible leakage sources.
Walls should be cured seven days under wet burlap prior to placing and compacting the backfill. Do not over-stress the walls by operating heavy equipment on the backfill, or by impacting against them with large masses of moving earth.
Fig. 2 Typical Hopper-Bottom Pool
FLOOR CONSTRUCTION
Two floor constructions are available. The time-proven method is a reinforced concrete slab at least 4 inches thick in small pools and 6 inches in larger pools. Reinforcing consists of welded wire fabric (mesh) with No. 4 AS&W gage wires (0.2253 inch diameter) at 6 inch centers, or of inch bars at 12-inch centers each way. Construction joints should be avoided; but if necessary, they can be made by keying and bonding the new concrete to the old. Floor reinforcement is continuous across these joints and extra reinforcement is desirable. Expansion joints are unnecessary in pools less than 50 feet in length.
More economical is a sand floor covered by a manufactured vinyl or nylon liner which extends up the block walls and over the coping. Liners are available from some block manufacturers as part of a complete pool package, including precise installation instructions. The dimensions of the excavation for a liner are critical, and the sand floor must be perfectly smooth. These liners are guaranteed up to ten years, but the pool must not be drained or the fittings will not realign correctly upon refilling. One third of new residential pools are