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Best Practices for Liquid-Applied WRB

RussellKM | Posted in General Questions on

I’m putting foam insulation to the outside of my 30 year old ISPs.  I will be taking off the current Tyvek and replacing it with a liquid WRB(Tremco 230 Exoair).   Any tips on best application practices for this ?

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  1. Expert Member
    ARMANDO COBO | | #1

    You can roll or spray it. I would hire an experienced applicator, as they usually know to apply the right wet thickness, good coverage and follow installation process correctly. It can make a difference on whether you waste your money or not. Contact manufacturer or retailer for an applicator recommendation.

    1. RussellKM | | #2

      Thanks for the information. There are not experienced applicators in my area that I can find, so I will have to rely on the manufacturer's advice. Thanks again. Russell

  2. JC72 | | #3

    Mind the movement of the building.

    "...Back to movement. Joints and inside and outside corners open up and close up all the time. The gaps get bigger and the gaps get smaller. Let me repeat the point here…they don’t just open up…they go back and forth. The water control layer we cover them with…the liquid applied membranes that are spray applied, brush applied, trowel applied, or whatever, need to be elastic. Think rubber band. There is elongation and recovery. There is cycling. There is fatigue. There is aging.

    There is more. There always is. The geometry of the joint and corner matters. Both the material properties of the joint and corner treatment and the geometry of the joint and corner matter.

    With a “difficult” joint and corner the material properties of the liquid applied membrane are a big deal. With an “easy” joint and corner the liquid applied membrane is stressed less. Not too many liquid applied membranes have the material properties to handle “difficult” joints. But with the field experience over the past two decades with liquid applied membranes we can turn “difficult” joints in to “easier” joints. The best combination of course is combining a high performance liquid applied membrane over a joint that has been made less stressful...."

  3. RussellKM | | #4

    Thanks for the advice and link. My house is very straight forward and except for a bump out that serves as a mud room, and where the wall meets the roof overhang, it is a 32' 6" square. I presume that the stress points to which you are referring are the corners of the house and the windows and doors. I will read your suggested link and see what I can learn.
    Thanks again, Russell

    2. Read the link. Good reading and a lot of good information. My house is a level two but I will not be using closed cell polyurethane as exterior insulation., so

    Question 1: the sealant needed at OSB joints and corners? Silicone, ?

    Question 2: How to achieve the 1/32" gap between liquid WRB membrane and the insulation boards? Or just make sure insulation boards can take on some moisture?

    Thanks again, Russell

  4. Expert Member
    Akos | | #5

    I know they are used a fair bit, but I'm still not too comfortable with liquid applied WRBs.

    You are relying on the sealant and caulk/tapes for WRB continuity, plus window details are always a reverse lap.

    Call me old fashioned, but I prefer my WRBs as lapped sheet goods that rely on gravity for drainage. As far as I know, gravity has never failed.

    In this case I'm struggling to see how a fluid applied WRB improves your assembly. Air sealing is much easier with a quality tape.

  5. RussellKM | | #6

    Thanks for the information. Here are what I see as the advantages of liquid WRB: seals around fasteners (used for strapping); no need for fasteners for the WRB itself which means no penetrations; continuous coverage for windows and doors; no need for tape.
    I have used TYVEK on the outside of my SIPS for the last 30 years and after stripping off some of the siding and some of the TYVEK, I am not happy with the way the TYVEK has performed.
    It has been suggested by Martin H. that the WRB on SIPS should be a bumpy housewrap in order to facilitate drying. Do you have any suggestions along these lines?
    Thanks again for helping me out with this before I start the work, hopefully in May.

    1. Expert Member
      Akos | | #8


      Walls are not roofs. They don't need to be liquid tight, nail holes just don't matter:

      There is even a site dedicated to this, my google foo is failing me currently so I can't find it.

      The bottom line, any properly installed WRB will work.

      The most likely reason you were not happy with your house wrap over the SIP is that there was no capillary break. It would have been pretty much the same no matter if the wrap was sheet good or self adhered. Without a capillary break, the small amount of moisture that will make it through the siding gets trapped between the siding and the OSB thus what you saw.

      Martin's suggestion of bumpy house wrap is the minimum to help with this. Even better, install rain screen strapping to add in a proper capillary break. Besides helping with keeping the sheathing dry, a capillary break will also significantly increase the life of any painted siding. Since it is a simple addition, it is well worth the small amount of extra work.

  6. GBA Editor
    Kiley Jacques | | #7

    If you haven't already, read this: Liquid-Applied Water-Resistive Barriers.

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