Spray Foam Insulation Tips
Never worked with two-part spray foam insulation before? Here's a guide on how to get in, get out and get the job done with no mess and no stress!
Basics of spray foam insulation
Closed-cell polyurethane spray foam has some pretty awesome qualities. It has a high R-value. It’s resistant to water, mold and insects. It expands into hard-to-reach nooks and crannies. Heck, it can even add structural support to walls and roofs.
Wear the proper gear
Protect your lungs with a respirator, and be sure to wear a full protective suit, chemical-resistant gloves and wrap-around goggles. Tape your gloves to your sleeves and wear your junkiest shoes. Acetone will dissolve fresh foam right away, but once this stuff cures, it has to be physically scraped off. In general, if you don’t want it covered with foam spatter, keep it away from the action.
Never spray a wet surface
Never spray foam on a surface with a moisture level of more than 20 percent—the foam won’t stick. If the surface you’re spraying hasn’t been exposed to water for a few weeks, it should be OK to spray. But if you’re patching a wall that recently sustained water damage, or was just assembled with new, wet lumber, you may want to test the moisture level before you spray. You can get a moisture meter here.
Make a plan before you pull the trigger
Before installing the first tip/mixing nozzle, point the gun into a garbage bag or empty box, and pull the trigger until both chemicals are flowing evenly. But long before you do that, plan your work.
Cover windows with plastic
Staple plastic to the framing around the windows (and doors). Don’t worry about covering the gap between the window and the framing because you’ll want to fill those with low-expanding canned foam specifically designed for windows. Cover all the switch and outlet boxes with masking tape so you don’t fill them with foam. You don’t need to use gasketed electrical boxes when you insulate exterior walls like you would if you were using fiberglass—the foam will air-seal around the box.
Lube the gun every tip change
The end of the gun needs to be lubricated before the first tip is installed, and again before the tanks are stored after use. Many pros prefer to lube the tip of the gun every time they install a new tip. Kits will come with some lubricant (petroleum jelly). Always follow the manufacturer’s instructions on operation, tip changes, storage and disposal.
Before filling the wall cavity, spray the perimeter with a 1/2-in. layer, which will expand to a 1-in. layer. These layers are called “lifts.” This will ensure that the foam penetrates any voids where the studs meet the sheathing. This also reduces the risk of bulges in the sheathing. If foam is sprayed into a large gap between the stud and the sheathing and is immediately covered by a thick layer, the pressure of the expanding foam can actually push out any sheathing that isn’t securely fastened. Wait a few minutes after picture-framing the cavity before you go back and lay down the first layer in the center of the wall.
Spray two-inch lifts and wait
Always wait a few minutes before spraying additional lifts, and never spray a lift more than 2 in. thick. The foam needs time to cure before being covered with another lift. Uncured foam results in reduced R-values. The allowable thickness of lifts varies by manufacturer, but all have a limit. The two most common spray foam installation mistakes are failing to wait for lifts to cure and spraying lifts that are too thick.
Spray the rim and the bottom plate
There should be a foam sill sealer between the bottom plate and the concrete foundation wall. But voids in the wood or concrete, or tears in the sill sealer, can create gaps where air and insects can penetrate. While you’re sealing the rim board, cover the bottom plate and top off the concrete as well. There’s no need to picture-frame the joist spaces before filling them, but don’t spray a lift more than 2 in. thick.
Scrape overspray with a curry comb
Run a straightedge along the outside of the studs and scrape down any high spots with a curry comb. Remove large chunks of foam with a handsaw. Curry combs are designed to groom horses and are available online or at farm supply stores for less than $10.
Combine foam with fiberglass
Fiberglass insulation can be used in conjunction with spray foam. The process is called “flash and batt.” Just picture-frame the wall cavities and lay down one lift, and then fill the rest of the cavity with fiberglass insulation. This is a popular way to save money but still take advantage of the outstanding air-sealing properties of foam.