Recently, I used Huber's Zip System Liquid Flash for the first time. It was on a remodeling project where we installed Zip System R-Sheathing on the walls (see JLC Oct/13) and 5/8 inch–thick Zip Panel on the roof. Huber designed Liquid Flash to be used in areas where Zip tape might not be easy to apply, such as pipe penetrations and window openings.
This liquid-applied "membrane" comes either in 20-ounce sausage packs or in 29-ounce cartridges and is covered by the same 30-year warranty as Huber's full system. It is relatively new—available since last summer—and we wanted to try it out on a few windows that we were installing, as well as on pipe penetrations, to see how it performs.
Sill pans. After making sure that the rough sills were free from debris, wood splinters, and other contaminants, we started off by running a thick bead of Liquid Flash at the corner of the rough opening. Next, we applied it in a serpentine pattern a minimum of 6 inches up the jambs, then across the sill in straight, parallel beads, filling in any irregularities by squeezing out a little more product. Last, we ran a bead on the outside face of the sheathing. We then spread the product out evenly using a disposable putty knife, being careful to spread it a minimum of 2 inches onto the face of the sheathing.
Liquid Flash is fairly sticky and has a tendency pull away from itself, so it's important to use enough product for proper coverage, especially at corners. Because it self-levels a little bit, we didn't have to overwork it. You can tell when you've achieved the minimum thickness of 12 to 15 mils: when you can no longer see the substrate underneath.
We used one 29-ounce cartridge to complete the sill pan on this 5-foot–wide window—framed in a 2x6 wall with 1 1/2 inch–thick R-Sheathing panels. Liquid Flash is a moisture-curing product; low temperatures and low relative humidity slow the drying time, while high temperatures and humidity accelerate it. The day we applied Liquid Flash was moderately humid and in the 70s; it took about 45 minutes to skin over and 4 hours to dry.
One more thing: Be sure to use Huber's recommended sealant for setting the window nailing fins. Initially, we tested Lexel, a solvent-based co-polymer rubber sealant, on some scrap Zip panel coated with Liquid Flash and it didn't cure. After talking with Huber, we ended up using 100% silicone sealant, though butyl and polyurethane are also acceptable.
Penetrations. At the roof, we sealed gaps around vent pipes and a PVC flue as a precaution until the self-adhering membrane, flashing boots, and shingles were installed. At the flue, we followed Huber's specs, which call for backer rod in gaps wider than ½ inch. At wall penetrations, which were blocked out for the siding, we put a bead on the top of the block, tooling it to create a fillet, again as a precaution until the flashing and siding were installed.
Costs. For a sill pan, Liquid Flash is more expensive than tape—$34 for one 29-ounce cartridge compared with less than $10 for 12 to 15 feet of 6-inch tape. (Liquid Flash took about 5 minutes less to apply than tape.) However, I'd highly recommend it for flashing mechanical penetrations.