Liquid-Flash a Windowsill Pan
Mastered in a Minute: Liquid flashing offers a seamless alternative to flashing tape.
Liquid flashings are great for making a windowsill pan that’s leak free. Here’s how to do it.
Before flashing, slope the rough sill to the outside so that if any water makes it to the sill, it will be directed outside. Here we installed a piece of beveled siding on top of the rough sill to create the slope.
Then, load a caulk gun with liquid flashing. Many products come in tubes or sausage packs, which make them easy to apply. Start by applying a thick bead to visible gaps, like in corners and where the framing meets the sheathing.
Then move on to the sill. Here we applied multiple beads to the sill, but you can also lay down a zig-zag bead. After that, apply liquid flashing at least 2 in. onto the face of the wall sheathing, and up the jambs by at least 6 in.
Then, spread the wet flashing to create an even skin without any holes. A plastic spatula, a stiff brush with the bristles cut short, or a putty knife can all be used to spread the product around to an even film.
The recommended coating thickness will vary by manufacturer, but in general, it needs to be applied thick enough so you can’t see the wood or sheathing through the flashing.
If framing or sheathing is visible, apply more liquid flashing to the area, and smooth it out.
Once complete, allow the liquid flashing to cure before installing the window. For products that are moisture-curing, the cure time can be shortened by spritzing the flashing with water. Dry times vary by manufacturer.