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Relative nastiness of various sealants

George_7224612 | Posted in General Questions on

In response to a question about sealing polyiso to a concrete floor, Michael Maines remarked that Tremco acoustical sealant is nasty stuff and suggested that Contega HF is as effective without the nastiness.  At my age, I’ll probably croak of something else before such nastiness will kill me but I’d prefer to avoid it if I can.  It would be interesting to know which products are lesser offenders.  Since I may use Tremco Dymonic 100 and ExoAir 230 on my project, I’d specifically like to hear whether anyone has an opinion on the relative nastiness of those products.

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  1. Expert Member


    First let me say that although I was the one who suggested Tremco acoustical sealant, I agree with Michael that when a comparable product with less VOCs like Contega HF is available, it's a good idea to use it.

    One thing that is worth thinking about when choosing sealants is whether they are being used inside the conditioned space. If not (putting aside any wider environmental concerns), I can't see where there are any potential health issues.

  2. charlie_sullivan | | #2

    From a glance at the SDS for each, I'd say the Demonic 100 is not necessarily any better than the acoustical sealant, although the nasty vapors might dissipate faster from the Demonic 100. I'm less sure about the ExoAir 230. Someone recently suggested Sashco Big Stretch and its SDS looked a little friendlier than the Tremco ones. I'm a fan of Contega HF.

    I'm not a real expert on reading SDSs but I try after being dismayed by the awful and persistent smell of Tremco acoustical, which I think is from the "residual oil" on its ingredients list. Residual oil is literally the toxic scum that is left over after crude oil is refined. I can't believe that "green builders" think that's a good thing to use inside their clients' envelopes.

  3. George_7224612 | | #3

    Thanks for the replies, gents. The ExoAir would be used on the exterior, but the Demonic 100 would be used to flash the rough openings. I suppose that once the windows are in and sealed, the inner seal would keep out any nastiness.

  4. Expert Member
    Peter Yost | | #4

    HI George -

    When it comes to chemical formulation of sealants, the leader in my book is Prosoco. They took the lead on Health Product Declarations:

    The "liquid flash" in the Huber ZIP system is a Prosoco sealant.


    1. cstarcher | | #5


      Sorry to dredge up an old thread, but is the ZIP Liquid Flash the same as either Prosoco FastFlash or Joint and Seam Filler? I'm curious if you could substitute one for the other.

    2. KauaiBound | | #6

      There are multiple STPE liquid flashing products available. Chemistry doesn't change meaningfully by brand (but price sure does!). Prosoco/Zip have engratiated themselves into the residential market and that's what gets talked about - almost never hear about other products because influencers aren't paid to promote them.

      Henry/Fortifiber has a STPE liquid flashing "Moistop" that sells for $8.50/20 oz sausage. Another STPE liquid flash - BASF MasterSeal NP150 - can be had for $10.50/20 oz sausage. 1/2 to 1/3rd the price of the others. Both are huge companies with large distribution chains offering economies of scale.

      1. cstarcher | | #7

        Thanks! This is very helpful. I had actually looked at the MasterSeal NP150 because of the significant price difference, but I couldn't find an example of anyone using it as a liquid applied flashing in the same manner as Prosoco and Zip. My application would be as an air barrier between the ZIP sheathing and the foundation.

      2. Patrick_OSullivan | | #8

        I don't know enough about the chemistry to be definitive with what I'm about to say, but this may be a case of "get what you pay for". This info comes from the SDS of each product.

        Prosoco Fast Flash: 10-30% STPE (large range as exact quantity is a trade secret)
        Zip Liquid Flash: 10-30% STPE (large range as exact quantity is a trade secret)
        Henry AirBloc LF: 10-30% STPE (large range as exact quantity is a trade secret)
        Henry Moistop Sealant and Liquid Flashing: 0.5-2% STPE
        BASF MasterSeal NP 150: 0.3-1% STPE

        1. vap0rtranz | | #9


          How common is HPD?

          I searched for "sealant" in the public HPD repository and came up with 309 results! Nice.

          Has anyone compared SDS datasheets across sealants?

          I thought a "Low VOC" labelling would be fine ... until I got up a few feet into a a floor joist cavity to seal up our rim joist. I was sealing with GE 100% Silicone #2 (Window & Door). Once it started curing, you should have seen me crawling backwards quick! I had to step away for 5mins to stop my noise from running, my head from pounding, and just to get fresh air again. :/

          GBA got me into checking SDS on this stuff. GE's SDS datasheet is alarming. They don't even know the toxicity of this stuff:

          "98.075 % of the mixture consists of ingredient(s) of unknown acute inhalation toxicity (gas)
          98.075 % of the mixture consists of ingredient(s) of unknown acute inhalation toxicity (vapor)"

          And you know its bad if stuff meant for waterproofing can still leach into water and stick around, with warnings like:

          "Harmful to aquatic life with long lasting effects."

          Nasty stuff indeed!!

          1. Expert Member
            BILL WICHERS | | #10

            >”And you know its bad if stuff meant for waterproofing can still leach into water and stick around, with warnings like: "Harmful to aquatic life with long lasting effects."”

            Not necessarily. Many silicones warn against their use in aquariums, often because they just don’t want to test for that, but sometimes because they contain anti-mold additives. Just because something says it’s bad in one application doesn’t mean it’s bad for everything.

            There is more to it than just “low VOC” too. What if you’re sensitive to one component even if there isn’t much in there? People aren’t usually sensitive to “chemicals” in general, they’re sensitive to one or two (maybe more) SPECIFIC chemicals. It’s like an allergic reaction in that respect, similar to how you can be allergic to cats but not dogs.

            BTW, silicone cures by the evaporation of acetone, so that’s where the nasty “silicone” smell comes from. As long as you’re not in a small sealed space, the stink of acetone usually goes away pretty quickly.


        2. cstarcher | | #11

          Thanks, Patrick. I hadn't looked at the SDS for these. Having looked at them, the Prosoco, Zip, and Henry AirBloc look much more similar chemically than the others. I wonder if this is significant in this application.

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