Do I need to use silicon sealant on normal PVC gutter joints?
No, the joint is sealed by the small rubber strip that is contained within all gutter unions, outlets, angles and stop ends.
As the gutter is clipped in place, the downward pressure applied by the fascia brackets forces the gutter down on to the seal, compressing it to create a watertight joint.
The efficiency of the seal however is increased by spraying with silicon lubricant prior to the gutter insertion. This helps to keep the seal free from dirt particles whilst improving movement across the sealing strip during expansion and contraction of the system, prolonging the life of the whole gutter system.