Why Does Screen Spline Keep Popping Out?

Spline that pops back out after being reinstalled is almost never a sign the mesh itself is bad. It is a sign the spline and the groove no longer fit each other. Spline is sized by diameter to match a specific channel width, and two things move that match over time on an older Casselberry frame:

• The groove widens. Every previous rescreen — and on a cage from the 1970s or 1980s there has usually been at least one — risks stretching the channel slightly if the spline tool was over-driven. A groove that has been through this twice no longer holds the diameter it was cut for.
• The spline itself shrinks. UV exposure hardens rubber spline over years, and hardened spline is both smaller and less able to flex into an uneven groove.
• The wrong diameter went in. A quick repair sometimes uses whatever spline is on the truck rather than measuring the groove first. It will hold for a while and then let go, which reads exactly like a fresh installation failure even though it was a sizing mistake from the start.

The fix is not re-driving the same spline harder — that widens the groove further and guarantees a repeat. It is measuring the channel and matching spline diameter to it, which is a five-minute check that most callbacks on this specific complaint turn out to be skipping.