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Community and Q&A

Applying Stucco over Foil faced foam

Dennis Levine | Posted in GBA Pro Help on

I am building a new home in Park City Utah at 7500 feet with an average winter high in the mid 30’s and lows in the high teens to low twenties…low humidity. I am planning to use 2” Hunter XCI
Polyisocyanurate foam core panel bonded to an impermeable foil facing material with a foil face providing an R value of 14.1. The foam is installed over tyvex and the interior walls will use a bib R23 system.

The lower portion of the house will be covered in masonry stone and the upper portion with Stucco. The stucco will be installed over the foam using a metal woven wire for the stucco to adhere to. May or may not use weather resident paper under the woven wire as it seems like overkill.

My questions are:
1) Is there issue applying stucco over foil based foam which is impermeable?
2) Do you have any suggestions regarding the Stucco prep and application?
3) Are there any issues regarding the install of the masonry stone?

Thank you,
Dennis

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Replies

  1. User avatar GBA Editor
    Martin Holladay | | #1

    Dennis,
    I suggest you read this article:
    To Install Stucco Right, Include an Air Gap.

    I'm not sure what you mean by "masonry stone." Is that different from a material that I call "stone"?

    Is it natural stone? Manufactured "stone" (that is, concrete that is made to look like stone)? Adhered thin stone veneer? Something else?

  2. Dennis Levine | | #2

    yes, i am using real stone on the outside

  3. User avatar GBA Editor
    Martin Holladay | | #3

    Dennis,
    I don't know whether your stone has an independent foundation, or whether you have a plan to try to adhere the stone to a wood-framed wall. I would be very leery of the latter approach.

    Both stone veneer and stucco require an air gap for drainage between the cladding and the sheathing, in my opinion. Both types of cladding are associated with a very high rate of wall rot problems -- so proceed with caution.

  4. Dennis Levine | | #4

    thank you for the link to the article. As I read this the stucco needs to dry when wet in both directions. a drainage mat is recommended to help the stucco dry, but this mat will be over an impermeable foil face which will not allow any drying to the inside. do you feel with a proper drainage mat the stucco will be able to dry properly if the moisture is trapped by the foil face of the foam?

  5. User avatar GBA Editor
    Martin Holladay | | #5

    Dennis,
    The article recommends (for stucco over rigid foam) that you install vertical furring strips over the foam, followed by paper-backed metal lath.

    The air gap between the vertical furring strips should be ventilated, with air inlets at the bottom of the wall and a slot at the top to provide ventilation at the top -- just like any other rainscreen gap.

  6. Dennis Levine | | #6

    Thank you, furring strips seems to be the solution. one final question, half inch to three quarter inch strips every 16 inches sound right to you? thanks agian

  7. Dennis Levine | | #7

    just found your article on Fastening Furring strips to Foam Sheathing...thanks

  8. Dennis Levine | | #8

    I come out the computer industry where the software companies blamed the hardware and vice versa. Installing stucco over foam to gain exterior insulation feels like it did in when everyone blamed everyone else. Now, I am a novice about green techniques but I feel miles ahead of the subcontractors I am dealing with.

    Relying on the information received from our local experts and comments from Greenbuildingadvisor I was planning on using a house wrap similar to Tyvex, attach 2” dual foil faced Polyisocyanurate foam with an R value of 14+ (based upon my calculations using the psychrometric chart), vertical furring strips over the foam followed by paper backed metal lath. A three stage stucco application will be the final step.

    The morning meeting with the Hunter foam Panel swears applying stucco over foil based foam is not a problem although he did not offer any application notes. Later in the day I met the stucco installer using Senergy brand, who said 1) stucco cannot be installed over a foil based foam as it will not adhere properly, 2) applying mud will penetrate the metal lath and fill the air chamber 3) the max polyiso foam size (non foiled based) stucco can be applied to is 1 ½” 4) the wrap between the foam and plywood sheathing needs to be a drainage wrap. Finally I met with my mason who does not want to use a rain screen since the lay is a dry stack so the moisture will escape via the space between the stones.

    I almost gave up on the exterior foam idea but want to preserver at least for a few more days. So my questions are:

    1. Is there an issue using foil on both sides of the foam?
    2. Does the paper backed metal lath provide sufficient adherence qualities for the stucco
    3. 1 1/2“foam does not meet my minimum R value needs, suggestions?
    4. Does the wrap between the foil based foam and Tyvex really need to be a drainage wrap
    5. Is there any issue applying large 18” x 18” x 5” stones or are furring strips not need behind the scratch coat and setting bed?

    Hopefully I have articulated this well enough where you can help.

  9. User avatar GBA Editor
    Martin Holladay | | #9

    Dennis,
    Q. "Is there an issue using foil on both sides of the foam?"

    A. The foil-faced foam is not an issue if you have an air space between the foam and the paper-backed lath, because the stucco doesn't touch the foam. However, your Senergy contractor is right that neither traditional stucco nor synthetic stucco can be adhered directly to foil-faced foam. If you are considering hiring a Senergy contractor, you won't have any problems coming up with details, because Senergy contractors don't install stucco -- they install EIFS. EIFS systems include exterior foam -- usually EPS -- and synthetic stucco. If you like synthetic stucco, then choose an EIFS system. That's the way to solve your detail conundrum.

    Q. "Does the paper-backed metal lath provide sufficient adherence qualities for the stucco?"

    A. I'm not sure what you mean. Paper-backed lath is designed specifically for stucco. However, EIFS systems don't use paper-backed lath.

    Q. "1 1/2 inch foam does not meet my minimum R value needs. Suggestions?"

    A. An EIFS contractor should be able to offer an EIFS system with R-14 (or higher) foam.

    Q. "Does the wrap between the foil based foam and Tyvek really need to be a drainage wrap?"

    A. Yes, that is a good idea.

    Q. "Is there any issue applying large 18” x 18” x 5” stones?"

    A. Of course -- there are huge issues. You have to get the details right, and you have to carefully think through the transition from stucco or EIFS to your stone veneer.

    Q. "Are furring strips not need behind the scratch coat and setting bed?"

    A. You can certainly detail a stone veneer wall without furring strips. The issue is the transition between your two types of siding. Both conventional stucco and stone veneer need an air gap between the cladding and the sheathing. In the case of stone veneer, you don't need furring strips to establish the air space; the details would resemble details used for brick veneer.

  10. Dennis Levine | | #10

    Thank you for your prompt response, i appreciate it. a few questions to tie this up
    1) not planning on using EIFS due to the negative posting. I assume for stucco it is the identical process, that is using paper backed metal lath
    2) like to stay with 2" and stucco, are you aware of any issues with this combination
    3) Drainage wrap. Tyvex is already up, can a drainage wrap be applied over the existing wrap?
    thanks

  11. User avatar GBA Editor
    Martin Holladay | | #11

    Dennis,
    Q. "I'm not planning on using EIFS due to the negative posting. I assume for stucco it is the identical process, that is using paper backed metal lath?"

    A. No, the details for EIFS are very different than the details for stucco. With an EIFS system, the synthetic stucco is applied to a fiberglass or plastic mesh that is attached directly to the EPS foam. There is no metal lath or paper.

    Q. "I'd like to stay with 2 inches of foam and stucco. Are you aware of any issues with this combination?"

    A. Whether there are "issues" depends entirely on the details used and the skill of the installer. Many stucco contractors refuse to install stucco using the recommendations in my blog (that is, including a drainage gap between the paper-backed lath and the rigid foam). However, conventional stucco applications are leading to wet-wall disasters in almost every state in the country.

    Q. "The Tyvek is already up. Can a drainage wrap be applied over the existing wrap?"

    A. Yes, you can install a wrinkled housewrap on top of your Tyvek.

  12. Dennis Levine | | #12

    thanks, will call a meeting and try and get everyone on the same page.

    EIFS systems use to have problems, have these been resolved and would you use it on your home?

  13. User avatar GBA Editor
    Martin Holladay | | #13

    Dennis,
    The old face-sealed EIFS are no longer installed. As far as I understand, all EIFS contractors in the U.S. are now installing water-managed EIFS. These systems have an excellent reputation and perform well.

  14. Dennis Levine | | #14

    you have been great! Thanks
    I might have a few more questions after my meeting.....again thanks

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