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Long-Exposed Rigid Foam Insulation

JohnL001 | Posted in General Questions on

We are having a new home built here in Arizona.  Foam board and wire mesh has been installed, but due to delays it has been sitting for about 8 to 10 months.  The foam board has turned yellow and is stained from the harsh Arizona weather.  Do you think it is still ok to apply stucco or will it cause problems ?  The plaster contractor says it should be ok.  Need a second opinion.  Thanks.

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  1. onslow | | #1

    John L,

    I would strongly recommend you contact the manufacturer of the materials being applied and have them weigh in. Any warranty issues could be negated as your problem if you grant permission to proceed. The fact that the wire has been sitting out for so long is less worrisome than the foam which does degrade in sunlight. I am assuming it is low density EPS foam rather than XPS which degrades differently. Both will have friable surfaces that will not make for good adhesion with the stucco. Imagine trying to put tape onto a dusty surface. Similar bond failure mode.

    EPS beads, especially in low density form, will lose the bonds with other beads as well as become physically fragile since the bubble shaped bits degrade in sunlight. It could be acceptable to create a fresh surface by abrasion of the degraded foam. Unfortunately, the wire mesh is in the way. It may also be that the foam layer is too thin to abrade and have anything left. Not an optimal situation in any case. Again, the code and manufacturer's requirements should rule.

    I suspect that the final coating process will represent thousands of dollars, so risking the failure of the job because the builder delayed an excessive amount of time should not be on you. It will likely be several thousand to pull and replace the existing work, so expect resistance.

    I am a bit curious as to the presence of wire. Is this a full hard three coat or a two step EIFs?

    1. JohnL001 | | #3

      Thanks for your suggestions. I will be contacting the manufacturer (Insulfoam). It is a Type 2, whatever that means. Pretty sure they are doing a 2 step system. Thanks again for your input.

  2. walta100 | | #2

    When you say “stucco” do you really mean modern synthetic stucco (EIF) or traditional missionary stucco.

    I agree with John that only answer you can get from the products manufactures will carry any weight with me. I suspect getting a yes answer from them in writing will next to impossible.

    I would not accept an EIF system over soft yellow foam.


  3. Expert Member
    BILL WICHERS | | #4

    The degredation you're seeing is probably either one (or both) of two things:
    1- The material has been bleached by the sunlight, but is still structurally OK.
    2- The polymer itself is breaking down from UV exposure, and the materials is structurally degraded.

    To test for #2, poke and scratch at some of the "damaged" areas. If the material is crispy/crunchy and you can easily poke your finger into it, that's bad degradation. If you can scratch a chalk-like dust off the top with your fingernail, that's minor degredation. If the only damage is bleached spots, discoloration only, that's not really a problem.

    I'd check with the manufacturer too to be sure, but chances are if it's not structurally degraded as described above in #2, you're probably OK and can continue with your build normally.


    1. JohnL001 | | #5

      Checked with the manufacturer (Insulfoam) and they pretty much agreed with your assessment.
      It seems to be structurally sound, but it does have the chalkiness on the surface. They said that shouldn't effect the bond of the first scratch coat since that is primarily bonding to the the wire mesh not the foam. So based upon that we are going ahead.

      Thank you for responding and the other responses I got too. Such a valuable resource and thanks again for taking the time to respond. Really appreciate it.

  4. Expert Member
    PETER Engle | | #6

    If this is either a one-coat modified cement stucco, or a traditional 3-coat stucco, you are probably fine. It is likely one of these (rather than EIFS), since these uses wire mesh and EIFS generally does not. With either of the cement stucco systems, there is no bond required between the stucco and foam surface. In fact, it is somewhat better if the stucco does not bond to the surface. All of the support and reinforcement for the stucco is through the wire mesh. You should verify that the wire mesh is fastened into the studs, not just into the sheathing, especially with a foam layer between the stucco and the WRB.

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