Attaching the Cap: After testing the fit, I applied thick beads of Phenoseal adhesive caulk to the PVC cap.
Attaching the Cap: Prepositioning the screws in their holes makes the installation go fast. When screwing through PVC this way, I always predrill tapered countersunk holes, then glue in plugs that I cut on site from scrap PVC. The plug-cutter and countersinks I use are made by Fuller (wlfuller.com). I trim the tops of the plugs off with my Tajima 18-point flush-cutting saw, sand the surface, and end up with a perfectly concealed screw.
Attaching the Cap: I frequently see rot around the sill on unflashed bulkhead doors; applying a rubber flashing under the existing housewrap before installing the unit is critical. Before sliding the cap into place, I always apply a thick bead of Phenoseal to the top edge of the cap where it meets the house, then secure it with pocket screws against the membrane, leaving a watertight joint.
Installing the Access Cover: Before installing the door unit, I always do a dry fit, just in case. There were no problems with this one, so after running a thick bead of caulking along the sides and top of the metal frame, I set it in place. I don't caulk the bottom in case any water needs to drain out. When you adjust these units for square, it's important to have both doors on so that you end up with an equal space between them.
Installing the Access Cover: After getting the unit in position, I predrilled holes into the cap, then followed with stainless steel screws. I've found that other kinds of screws always rust, leaving stains on the metal and concrete. Next I cleaned off the caulk squeeze-out between the metal unit and the cap, then added a strip of 3/4-inch PVC across the top, against the wall. I installed an aluminum cap flashing over the PVC strip, sealing it to the rubber membrane on the wall before reinstalling the vinyl siding.
Installing the Access Cover: Finally, I parged the existing curb. First I removed loose mortar and repacked the larger gaps, then I brushed on Weldbond (weldbond.com), a bonding agent that seals the porous concrete and helps the new mortar adhere. I immediately followed with the new mortar. To close up the gaps between the curb and the PVC trim, I used a tube of Quikrete mortar caulk; I applied this to both the inside and the outside of the frame and cap. This project took me about two days, including the time to remortar the curb. Depending on the amount of extra repair work involved, bulkhead replacements typically sell for $1,500 to $2,500.