Question: How do you seal the flashing beneath precast copings at the locations of dowels?

Answer: There are several ways to seal flashing around dowels for copings. The methods vary depending on the type of flashing. With copper, lead-coated copper, galvanized steel, or terne-coated stainless steel, I recommend soldering on a thin sleeve that will fit over the dowel as shown in the figure. You may need to separate the flashing sleeve from the dowel to avoid galvanic corrosion depending on the metals used. Another method is to make a hole in the flashing and seal between the dowel and the flashing with a compatible sealant or mastic. A high-grade construction silicone can be used for most metals. Consult the flashing manufacturer for the best sealant to use with plastics or composites.I prefer the first approach. It is easier to inspect the quality of the soldered joint versus the quality of the sealant joint.