Using Liquid Flash at a Wall-to-Foundation Connection
Brian Pontolilo demonstrates how to air-seal where the concrete foundation, mudsill, and ZIP System sheathing all meet.
Sponsored by ZIP System
For the house my wife and I are building in northwest Connecticut, we used ZIP System sheathing on the walls. Like many of today’s water-resistive barriers, ZIP System is great because it allows you to really efficiently take care of your water management and air-sealing at the sheathing level. Today, we’re working on the transition from the foundation to the wood framing above using liquid flashing.
The mudsill is a critical transition for a number of reasons. First of all, this is an area that’s going to see a lot of water. Rain splashes on these walls, and you can tell that this is the case when you’re building a house because you see the dirt getting splattered up there all the time. Secondly, we have dissimilar materials—wood and concrete—coming together and both behave differently, so this is an area prone to air leaks.
We took a little bit of a belt-and-suspenders approach down there at the mudsill. First of all, when we were installing the mudsill, we made sure to use a capillary break and we put beads of sealant on both the bottom and the top of that capillary break. This is to keep water out, but even more importantly for air-sealing. Where the wall comes down and meets the foundation, we’re sealing the joint between the concrete, the mudsill, and the sheathing with Huber’s Liquid Flash. The process is pretty simple.
First, we cleaned off the concrete and the sheathing by taking a broom and knocking off any splatter from dirt that made its way up there during the building process.
Second, we cleaned off the ZIP tape that comes down to the bottom of the sheathing with a little bit of acetone to get the release agent off of the tape. Then, we put a bead of tape along the foundation. We used duct tape for this, which is what we found sticks best to the green concrete. That’s just to give us a nice crisp line where the liquid flash ends on the foundation, because it will be a little bit visible. We don’t care as much at the sheathing since it’s going to be behind the siding.
The critical place to get the liquid flash is right into that joint. In a perfect world, your mudsill will be flush with the outside of your foundation, but that doesn’t happen all that much. In this project we had as much as a 3/8-in. overhang, so we needed to really make sure that we got a lot of sealant up in that area. I got a bead right in that corner where the concrete, the mudsill, and the sheathing all meet. Then I put a bead of seal along the concrete and spread that out with the spreader that ZIP supplies. I put a bead along the sheathing and I spread that out again nice and even.
Huber calls for 12 mils of thickness, but they also say that as long as you can’t see the substrate below, you’ve applied enough of the liquid flash. In other words, if you can see the concrete or if you can see the ZIP, apply some more. The last thing to do—before the liquid flash cures—is to pull the tape off for a nice, crisp line.