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Community and Q&A

A Look at Sealant Terminology

jonny_h | Posted in Green Products and Materials on

One of the learning curve issues I keep coming across on things related to construction is generic / vague terminology surrounding certain products.  I’ve posted in the past about types of tape, so here’s another one that I come across a lot: Various types of sealant-like things.

Plenty of installation details for various things have phrasing like:
“Bed [item] in a continuous bead of sealant”
“Caulk around edge of [item]”
“Use non-curing sealant (supplied by others)”
“Apply lap sealant to edges”
“Use acoustic sealant”
Rarely are specific products called out, and sealant products themselves like to use terminology like “all purpose” and “general purpose”, masking a whole world of material compatibility and application suitability.  Personally, I’d like to (a) minimize the number of different products I need to buy & keep track of, and (b) choose products that are “greener” / low-VOC / safer to use, especially in indoor applications, but without drastically impacting durability / performance.

Here’s what I’ve determined so far, and some open questions:

EPDM lap sealant: This appears to be a specific thing, for a specific application.  Nothing can be used in its place, and it can’t really be used for anything else.  It’s probably very solvent-y but at least it’s an outdoor application.

Non-curing sealant: This is a new one that I came across in some roof flashing instructions.  Appears to be some form of butyl goo that stays gooey (“non-curing”), which would disqualify the other types of “roof goo” that I already have (Chemlink M-1 and Duralink 50, which are described as moisture cure polyether sealants).  Any specific products that are recommended here?

Other exterior sealants: The aforementioned Chemlink M-1 and Duralink 50 I’ve selected for a few specific applications around flashing roof penetrations using Chemlink’s system.  Seems like these would be useful for a variety of exterior applications too.

Interior / Exterior sealants: I’ve got a bunch of Proclima Contega HF (“green goo” as my helpers affectionately call it) that I’ve been using as a general-purpose sealant, mostly for air barrier stuff where my usual selection of tapes needs a bit of help (weird corners, sealing membranes to masonry).  Seems to be a relatively “safe” chemistry

Acoustic sealant: I’m not really sure what this is supposed to be, to be honest… But it seems like my Contega HF would work wherever it seems to be called for.

Silicone caulk: Seems to be the best thing for specifically around bathroom fixtures, but seems to not be the right thing for a lot of other applications that DIYers tend to use it in.

So, anyone have thoughts on the broad topic of “gooey products applied with a caulk gun”?  Specific product recommendations?  Commentary on “non-curing sealant” or “acoustic sealant”?

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  1. Andrew_C | | #1

    I have vague-ish memories of articles by Peter Yost (?) on the topic of "sealants" and related. Couldn't find it in first Google search. But I did find a response of his in a previous Q&A that might provide some direction:

    Peter Yost | Jun 20, 2019 10:40am | #2
    Boy, it is really hard to find explicit and delimiting definitions of the terms caulk, sealant, mastic, etc.

    Here is my quick cut:

    1. adhesive: meant to be applied between two substrates to augment fastener connection of the two substrates. Adhesives are meant to be compressed/trapped.

    2. sealant - usually means liquid sealant and applied as a 3-D bead. These are meant connect two substrates, NOT compressed, and also installed with either backer rod or bond break tape to limit their attachment to the substrates to two unconnected planes, so that the sealant accommodates movement in connecting the two substrates.

    3. mastics: sticky stuff meant to seal surfaces, often left exposed

    4. PSA tapes: pressure-sensitive adhesive tapes meant to seal substrates and often accommodate some movement in the substrates regardless of whether or not the substrates are exposed or trapped by subsequent layers of the assembly.

    the most common chemical composition of many of these sticky materials include latex, modified bitumen, butyl, acrylic, silicone, and silyl/silane modified polymers. Each vary in their elasticity, accommodation of movement, environments they tolerate, strength of adhesion, outgassing, and cost.

    that clears things up, right?


    1. jonny_h | | #12

      Hm, was it this article: -- I just stumbled upon it while researching and it provides a quick overview of different sealant chemistry, at least as the field stood 10 years ago

  2. plumb_bob | | #2

    Very good question, and I look forward to further responses.
    Acoustic sealant is a bituminous caulk that is supposed to absorb sound waves, but I most frequently see it used as part of an air barrier, usually sealing either poly sheets together, wrb sheets together, or either sheet material to framing. I believe it is designed to maintain some plasticity over time so it will not crack and compromise the air barrier. It is generally terrible to work with because it sticks to anything and is hard to clean up.
    Silicone is a multi purpose sealant that stays flexible and is often used in baths and kitchens to waterproof at changes of materials, like from sink to wall or tub to floor.
    Latex caulks are used to detail trim and other finishing items prior to paint.

  3. charlie_sullivan | | #3

    The usual acoustic sealant is effective for air sealing, but is horrible in that it continues to emit nastly smelling VOCs for many months, maybe longer. It's made from a mix of leftover hydrocarbons from the oil refining process, and so many of them are bound to be toxic. You are very much on the right track in using Contega HF instead of acoustic sealant.

    Contega HF is great for sealing things that aren't exposed. It remains soft and flexible, which is good for maintaining a good seal, but makes it a poor choice for anything visible.

  4. Expert Member
    Akos | | #4

    Here is what I use.

    Air sealing, vapor barrier ("acoustic sealant" jobs)

    -green glue sealant (not the compound, the one in the black tube). Easy to apply, cleans up with water, stays flexible. Stay away from the official acoustic sealant unless your inspector requires it as gets on everything and impossible to clean.

    Trim/siding metal flashing:
    -OSI Quad, can get it color matched to most siding colors, holds up great. Occasionally, for a lot of black, I get some Dymonic 100 as it is cheaper.

    I've stopped using silicone in bathrooms. Tubs/showers get kerdi so need to caulk anything and sinks a backsplash. This way there is no caulk to get moldy and no maintenance.

    1. PatriciaCranberry | | #5

      This "no silicone" surprised me. I have a one year old kerdi shower (base and walls) but my contractor used "something" at the small gap between floor tile/wall tiles. And its a really small of course the material sagged or got pushed in during application (holds water) and now I'm seeing the beginnings of mold. If I were to scrape this material out, I never considered not replacing it with something. My thought was scrape it out. Replace it with good bead of silicone using my cramer silicone profile tools. Hard to break old habits.

      1. Expert Member
        Akos | | #10

        With a proper kerdi install, the shower should be liquid tight. This means you should be able to fill your shower pan up to the curb and no water will leak out.

        If this is the case, the silicone is not serving any purpose, if anything it is preventing any water that makes it behind the tiles from draining out. Best is to scape it out, clean the surface and grout the gap with matching tile grout.

    2. AC200 | | #7

      "I've stopped using silicone in bathrooms. Tubs/showers get kerdi so need to caulk anything and sinks a backsplash. This way there is no caulk to get moldy and no maintenance."

      That's a really interesting that makes sense. I still scrape moldy silicone caulk every few years and redo it with new silicone. I then grumble when my "20 year" mold resistant caulk gets a few black spots under it after a year. Wash, rinse, repeat. Going to ask my builder about this on the new build.

  5. GBA Editor
    Kiley Jacques | | #6

    This is such a good and well-articulated question, Jonny. I'm sure many people find that category of products confusing for the reasons you named. It warrants an article; I'll get it assigned. Thanks for the idea.

    1. AC200 | | #8

      Yes, it's a great idea! if there is any way work material compatibility into it as well. I often wonder about checking adhesive/sealant compatibility on manufacturer websites.

    2. jonny_h | | #13

      Thanks Kiley, looking forward to the article!

  6. plumb_bob | | #9

    Acoustic sealant can be used with sheet materials without the terrible mess with this approach:

    Fasten the sheet to the wall or ceiling, but leave the fasteners back from the perimeter of the sheet about 6" (hard to do if you are not used to this method), this will leave a flap of sheet. Put up all the sheets in this manner, and then come back and apply the bead of sealant, sticking the flap to the bead as you go. Works pretty good actually

    1. Expert Member
      MALCOLM TAYLOR | | #11


      There are no doubt builders who can do that, but I've yet y yo spend a day using Tremco acoustic sealant when it doesn't end up on me, my tools, truck seats, and the cat once I get home.

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