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How do I contain acoustical sealant toxity?

user-1101025 | Posted in Green Building Techniques on

Acoustical sealant was applied to tu-tuff as the vapor barrier for our crawl space.
This was phase one before going to phase two which would be use the supply and return
air sources to ventilate the area. The sealant was only used to adhere the vb to the concrete foundation wall. The sealant is superior becomes it does not dry out; hence, it maintains a seal
for radon remediation as well as a vb.

THE issue, though, is that the sealant is toxic and does not cure. The installer actually became ill and had to quit on day one. He returned to finish the job, but not very happy. At this point, I am awaiting his return to use maximum strength duck tape to seal the vb perimeter against the foundation. He started but ran out of tape.

Meanwhile, five days later, the vapors are still very strong. The laundry area adjoins and my wife reports feeling a loopie if she remains too long.

I stepped this one thinking that I was doing the right thing. I guess being “green” does not necessarily mean being safe. At this point I think that I may need to abandon the application of theory that says to treat your crawl space as your home and abdicate to the competing theory which calls for treating it more like your attic—insulate it away from the living space and provide ventilation.

Any suggestions? Is there a proven method of having an exhaust fan at one of the crawl space and a passive vent at the other. The downside is that the crawlspace will no be open to extreme temperatures and humidity. We live in northern Kentucky area.

Being more optimistic….does the sealant stop off gassing after a few weeks?

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  1. GBA Editor
    Martin Holladay | | #1

    You raise several issues.

    1. I don't believe that the fumes from acoustical sealant are toxic, although some people may be sensitive to the odor.

    2. There are several ways to keep the air in your crawl space separate from the air in the living space above, which I will describe below.

    3. You can use a high quality European tape (like Siga Wigluv, which is available from Small Planet Workshop), to seal polyethylene to your crawl space walls.

    I urge you to read Building an Unvented Crawl Space. The article describes two ways that a sealed, conditioned crawl space can meet code requirements. The method that would make the most sense for your situation would be to install a small exhaust fan in the crawl space (to depressurize it) along with a floor register that allows conditioned air from the upstairs to enter the crawl space, replacing the air that is removed by the exhaust fan.

    It's also possible to leave the crawl space unconditioned, and to avoid any connection between the crawl space and the house above. This approach requires a high degree of air sealing and attention to duct tightness. You also need to monitor the humidity level in the crawl space to be sure it stays under control. In some locations, this approach might not work.

  2. user-1101025 | | #2

    Thank you for the rapid response and suggestions for ventilation. I am totally on board with trying
    to depressurize the crawl space. If we can just keep a minimum of negative pressure, if I have the terminology correct, to the outside then I think that we will accomplish our goal. Instead of the suggested floor register what would you think about leaving a small area where the basement interfaces with the crawl space? Currently, the wall of contact goes almost to the top of the upstairs subflooring and we have an open staircase (no basement door from the first floor). In essence an exhaust fan on the exterior wall of the crawl space would have a chance to reliably pull air in from the upstairs conditioned air. So, I was thinking about using something like roxul or rigid reflective foil insulation to seal off the crawl space, except for area that would be about one foot by six inches. Sound ok?
    As for an exhaust fan, do you have opinion as to whether or not it should be continuous vs intermittent? The only reason that I can think of for intermittent is that maybe a continuous mode iwould over tax how much air is available to be drawn in from outside. Another detail is how strong of an exhaust fan? Would 50cfm be too little? The area of the crawl space is about 700 sq ft. I'm currently looking at the Panasonic Whisper line of exhaust fans, normally used for a bathroom.

    Re toxicity of the acoustic sealant, the box states in rather strong language that the off gassing is very toxic. (Tremco is the brand.) And, the contractor looked and said that he didn't feel too well even when he came back the second day to do some additional taping. He's a pretty tough dude. I suppose that over an additional time period there might be a crust that forms but I think this stuff stays very gooey.

    The european tape is a good idea. Perhaps the top of the line ...max strength duck for a little while but may not have the thickness in adhesion that you referenced.

    I'll call tremco and see what they have to say.

  3. GBA Editor
    Martin Holladay | | #3

    Q. "As for an exhaust fan, do you have opinion as to whether or not it should be continuous vs intermittent? ... Another detail is how strong of an exhaust fan? Would 50 cfm be too little? The area of the crawl space is about 700 sq ft."

    A. The answers to your questions can be found in the article that I urged you to read: Building an Unvented Crawl Space. In that article, I wrote: "The code lists two options for conditioning unvented crawl spaces; both options require the installation of a duct or transfer grille connecting the crawl space with the conditioned space upstairs. Option 1 requires 'continuously operated mechanical exhaust ventilation at a rate equal to 1 cfm for each 50 square feet of crawl space floor area.'”

    According to that formula, the required ventilation rate is 14 cfm.

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