Replies

1. 
   Riversong | Feb 16, 2010 11:30pm | #1

   Have you considered intumescent putty, such as STI's SSP? They even make a putty pad specifically for electrical boxes. Applied by hand, stays flexible. Rated for up to 3 hour fire walls.
   http://www.stifirestop.com/product_information/product_selector/ssp_putty.html

2. 
   Greg Xikes | Feb 17, 2010 12:08am | #2

   We looked at the putty pads but felt they would not create a good seal at the front of the box and to the back of the drywall.

3. 
   Riversong | Feb 17, 2010 12:24am | #3

   I don't know if it will satisfy your fire code, but for air sealing outlets I've always used Lessco polypans (as part of the air-tight drywall system). Then sealant is required only where the cables penetrate the pan, which can be filled with fire-resistant mineral-fiber or cellulose insulation.
   http://www.lessco-airtight.com/

4. 
   Garth Sproule | Feb 17, 2010 02:05pm | #4

   Nutek makes airtight switch boxes with a built in drywall gaskets...2 hour fire rating.

5. 
   Michael Chandler | Feb 17, 2010 03:14pm | #5

   On my own house I used the regular intumescent fire caulk and, after inspection, covered it with regular duct mastic to hold it in place long term, cheap except for the time and attention to detail required.

   For my clients I just use the intumescent fire caulk and airtight drywall detailing.

6. 
   Ine | Feb 17, 2010 06:53pm | #6

   I used the Airfoil boxes in my exterior walls. http://www.airfoilinc.com/index.html They have been really easy to work with and seal. I've been using spray foam but I would think a fire rated sealant would also work in these if the boxes meet your code.