Seals, Laps, Outlets, and Screws:

            At areas of offsets, it is important to seal the connection of downspout to elbow with Geocel caulking and securing with pop rivets on all sides.  The alternate method of placing two or three screws on the connection and not caulking the joint will not necessarily result in the joint leaking (as long and laps follow the flow of water), but the connection will be susceptible to corrosion and damage.  In addition, using screws in

place of pop rivets here will not give a secure enough fastening as in over time the screws tend to make themselves loose.

            Wherever laps and joints in the gutter or downspouts occur, caulking must be used between the overlapping material as well as over the exposed seamline.  This double caulking will ensure that there will be no leakage.  The Geocel 3100 Polyurethane Sealant as specified has proven to be the most effective and longest lasting caulking available.  If an alternate caulking is used, be sure that it conforms to the same federal standards as Geocel:  TT-S-00230C, Type II Class A;  CGSB CAN2-19.13-M82, Type 2, Class B;  ASTM C-920-86, Type S, Grade NS, Class 25, SWI 1D and 2D;  and AAMA 802.3 and 805.2.

            Outlets must always be used where the gutter connects to the downspout section.  A 2 3/4” round outlet has proven to be the most versatile and efficient size when being used with a 2 inch by 3 inch downspout.  A 3 inch by 4 inch outlet is most effective when being used on a 3 inch by 4 inch downspout.  In an effort to cut costs, some contractors will eliminate the use of outlets, choosing instead to cut an X shape in the gutter and pushing the flaps down, and placing a screw on each flap to the downspout.  This method is of poor quality and will most certainly lead to leaks to the top of the downspout in the near future.  

            Be sure that all screws being used on your aluminum gutters are made of stainless steel.  Because of the properties of dissimilar metals and the chemical reaction that occurs when they are brought in contact with each other, steel or zinc screws will rust and begin to corrode the aluminum gutter in a matter of weeks.  The only safe material to use is stainless steel (a neutral metal) or aluminum.  Pop rivets being used must have a stainless steel or aluminum rivet head and mandrel.