At the time, the boilers were sealed with a cement-like substance which required days-if not weeks-to set properly, time would not allow this and the seal quickly failed once the trial runs were restarted.
The boilers were sealed with a cement. This was at the time. Time would not allow this. This is like substance-if not weeks-to set properly. This is at the time. The seal quickly failed. This was at the time. The trial runs were restarted. This substance required days.