Why joint age changes the freeze risk calculation in Oreland, PA
Most pool closing companies do not distinguish between closing a pool at 60 years of service and closing a pool at 15 years of service. They follow the same process, apply the same blowout procedure, and make the same assumption that if the blowout appears to go correctly, the circuits are dry. On a 15 year old pool with joint material still reasonably close to its original condition, that assumption is usually safe. On a 60 to 70 year old pool in Oreland, PA where the joint material has been hardening through six decades of thermal cycling, it is not.
Joint material does not fail all at once. It loses flexibility and structural reserve progressively across decades of thermal cycling. The joint that was fully sound in 1980 at 20 years of service was somewhat more brittle in 2000 at 40 years of service and is considerably more brittle now at 60 to 70 years. As that brittleness increases, the joint’s ability to absorb the expansion of freezing water adjacent to it decreases. A low spot that retained a small amount of water despite a thorough blowout on a pool with original joint flexibility might freeze and expand without producing a failure. The same low spot on an Oreland, PA pool at 60 to 70 thermal cycles does not carry the same margin.
This is specifically why pressure verification after every circuit blowout on Oreland, PA pools from the 1950s and 1960s is the step that actually completes the closing. A circuit that holds air pressure after the blowout is dry. A circuit that loses pressure has water somewhere along its run that the blowout did not reach. Addressing that residual water at closing costs nothing extra. Discovering it as a failed joint after a January freeze costs the full repair, the disruption, and the delay to the following spring opening while the repair is completed.