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Building a Swimming Pool (continued)

Preparatory work

Before the work began, the clay sub-soil had to be tested for sulphates that might attack concrete. According to the Building Research Station's Digest No. 31 on "Concrete in sulphate-bearing clays and ground waters", the upper limit of safety was 0.2 per cent of S04 (dry weight). Some boys set to work to dig up clay samples from different depths, and found that below 6 ft. 6 in. a layer of pure clay began; one sample was brought up from 8 ft. deep and another from 12 ft., and both were sent to the Metropolitan Water Board for analysis. Their sulphate content was found to be .025 per cent and .03 per cent respectively, so no trouble need be anticipated from that quarter.

There was a great deal of other preparatory work to be done. Electricity and water had both to be brought to the site, electricity for a Kango hammer and water both for constant use during construction and later on for filling the pool. The local Water Board would consent to nothing larger than a 1 in. inlet, which meant that the pool would take a whole week to fill; but with the recirculation system of filtration to be installed, one fill would last indefinitely. Not only had some necessary water to be brought to the spot, some unnecessary water had to be got rid of, and the disposal of surface water which collected during construction presented awkward problems for months on end.

Other off-site preparations included the bending of the steel reinforcing rods, the stripping of the ex-railway trough wood of rusty nails and screws, and the preparing of the wood for rough shuttering - for although Wimpey's metal form work was to be used for the walls of the pool, strong barricades of wood would be needed to prevent landslides of the heavy clay surrounding the hole. On-site preparations would begin with marking out the hole to be excavated, the mechanical digging of the channels for the main sewer and the storm water drains (an outside firm asked £337 for this job alone), the mechanical excavation of the hole and its subsequent trimming to the exact dimensions needed, and the putting down, over the entire floor of the hole, of a "blinding layer" of weak concrete to give a clean working surface for the floor of the pool.

July 1962 July 1962.

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