GBA Logo horizontal Facebook LinkedIn Email Pinterest Twitter Instagram YouTube Icon Navigation Search Icon Main Search Icon Video Play Icon Plus Icon Minus Icon Picture icon Hamburger Icon Close Icon Sorted

Community and Q&A

Best foundation-to-sheathing flashing/sealing solution

88Clayton | Posted in Green Building Techniques on

I need to seal off some pretty large gaps at my sheathing to foundation junction.  I’m considering the use of Grace Vycor Plus.  If that is an acceptable tape, what is an affordable and compatible primer product that can be used to increase its tenacity on uneven, porous surfaces like concrete.

Please see the attached picture.  The surface not a straight line as I had hoped.  It cuts in and juts out as it progresses from Zip-R sheathing, past the bottom plate, then down to concrete.  Considering the shape, should I worry about following the contour of the surface, or just stretch tape over the gaps, making contact with with Zip-R and concrete only?

Furthermore, is tape even the best product here?  Or should I use a foam or caulk type product instead?

Thanks in advance for the tips!

GBA Prime

Join the leading community of building science experts

Become a GBA Prime member and get instant access to the latest developments in green building, research, and reports from the field.


  1. Expert Member


    Choose an appropriate tape from the various backyard tape tests that have been posted on GBA. Make sure it tis fully adhered to all the surfaces, not stretched over them.

    I'm a bit confused by the picture. How did you end up with the sheathing not extending down to the sill plate? The nailed connection between it and the sheathing is an important part of the continuity of the structure.

  2. 88Clayton | | #2

    Thank you. I’ve skimmed through at least one backyard tape test article. I’ll be sure to dig further. Do they talk about primers to increase adhesion?

    No good answer on the short sheathing other than my contractor employing woefully unskilled Mexican labor to frame the house after telling me they knew how to do Zip system. This was far from the only inadequacy and mistake resulting from their work.

    1. AJ__ | | #3

      You might want to consider the detail seen 2 minutes in to this video as a solution

      1. Expert Member
        MALCOLM TAYLOR | | #4


        Maybe that's what I'm seeing - a piece of blocking rather than the bottom plate?

        1. 88Clayton | | #5

          My picture is showing bottom plate.

      2. 88Clayton | | #6

        That’s great. I’m guessing that 2x2 is nailed straight into the bottom plate

        1. AJ__ | | #8

          It looks that way, yes.

  3. Jon_Lawrence | | #7


    I used Siga's Fentrim for that location and it worked great. No priming necessary and it even sticks to PT, which some tapes do not. I also caulked the seams first with Prosoco's R-Guard, but in retrospect, the Fentrim alone would have sufficed. It looks like the first inch or so of your foundation wall is not very smooth which might be a bit tougher to air seal, so you can get a wider width of Fentrim (I believe you can up to a 12" wide roll) so the tape on the foundation wall reaches the smoother section.

    1. 88Clayton | | #9

      Thank you for the recommendation. I think possibly 9 inch width will work.

    2. GBA Editor
      Martin Holladay | | #10

      Jonathan and Clayton,
      Fentrim is, indeed, a good choice. Either Siga Fentrim or Pro Clima Contega Solido Exo would be recommended in this location.

      1. 88Clayton | | #12

        Thanks, Martin. Sounds like maybe I should cough up the extra money and opt for one of the tapes you mention instead of the Grace Vycor Plus. I'm willing to do this, especially if a primer would not be required.

  4. Jon_Lawrence | | #11

    I used the Solido Exo for my windows and it worked well there. The Fentrim is thicker and feels stronger so less likely to get punctured on the rough surface of the concrete. Btw, Fentrim comes in both black and grey. The Fentrim on the south side of my house that saw extended periods of sunlight developed bubbles. Apparently I am not the only one. Siga now has a light grey version which does not have the same issue.

    1. 88Clayton | | #13

      Thank you, Jonathan.

  5. Stockwell | | #14

    I first filled the cracks with Prosoco Joint and Seam filler and then taped over it with Contega Solido Exo(6"). I found excellent adhesion to concrete without a primer. Solido Exo is a very flexible tape that can adapt to irregularities in the surface. This is in stark contrast to Zip tape, which is another excellent tape, but it has no flexibility. The Solido Exo was perfect for flashing my windows, which were installed over furring strips. It adapts readily to the furring strip-to-sheathing junction.

    The combo of liquid flashing and tape does a great job at keeping out bugs and air sealing.

Log in or create an account to post an answer.


Recent Questions and Replies

  • |
  • |
  • |
  • |