Air Sealing – Low Pressure Foam
johnwtaylor
| Posted in General Questions on
Instead of using 5mil poly and acoustic caulk I’m wondering if 2-4″ of low pressure (Frothpac) foam would air seal the space between the floor joists where they meet the rim joist?
Are there any chemical differences between low pressure and high pressure foam?
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Replies
I think you're talking about air sealing and insulating your rim joist here? You wouldn't normally use poly and acoustic caulk here. The two common ways to air seal and insulate a rim joist are to either cut pieces of rigid foam to fit and then seal them in place with caulk or canned foam, or just spray foam the entire area.
Frothpac isn't "low pressure" foam, it's a two-part closed cell spray foam. "Low pressure" foam stays squishy after curing, and is commonly sold as "door and window" foam in a can. They are a little similar chemically, but they're certainly not identical products.
There isn't usually a problem using one of the frothpac kits to spray foam a rim joist. The things to watch out for are to get the two cynlinders warm before application (commerically I like to set them on top of a transformer overnight, with residential projects put a space heater in a small bathroom, then close the door with the frothpack kit inside). I've found these kits work best when the cylinders are noticeable warm to the touch. DO NOT heat them up too much though -- you don't want them HOT. If you can't stand the heat, then it's too hot for the frothpack kit.
When you're ready to start foaming, first make sure ALL of the rimjoist area is clean and clear, and there are no obstructions. The goal is to be able to keep foaming once you start, and don't stop until you're done. Every time you have to stop for a bit to clean something or remove an obstacle, you need to get a new tip for the frothpack kit and you have to waste some foam to "prime" the new tip. Things work best if you can just move from one joist bay to the next along the rim joist doing a quick "blast, move, blast, move" foaming each joist bay as you go in rapid succession.
Bill
Hi Bill
You deciphered my question correctly.
I've sprayed ccPSF in the past but never used a Frothpac.
I'd heard there was a difference between the moisture transfer rates of Frothpac and ccSPU.
Thank You for the information
John
There may be some differences between the Frothpacks and other types of spray foam since there are many different foam formulations out there. You'd need to refer to the technical data sheets for the specific products you're considering using to know for sure.
Bill