Cap Joint Sealing – Place attachment screws 1″ from Cap ends and seal joint with a tooled flat silicone bead. Always clean joint first with rubbing alcohol. Expansion joint may be needed for movement, if installed during colder weather, as movement will occur in the hot weather.
We highly recommend Dow 999 Plastic Compatible Silicone
See 8 – 25mm Polycarb some are 20 Yr Warranty – Lexan Thermoclear is clearly the industry leader