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Thread: how to attach and tape rigid foam

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    DIY Senior Member Master Brian's Avatar
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    Default how to attach and tape rigid foam

    Needing to attach some rigid foam insulation panels to a concrete block basement foundation wall. Do I use liquid nails or something else?

    Also, how do I go about taping the seams? Is there a special tape or could I possibly even use gap and crack spray foam? Not sure if that would eat into the rigid foam, if not it would seem more permanent than a tape.

    I will be building a 2x4 wall over the rigid panels, then insulating the 2x4 wall cavity with either fiberglass batting or cellulose, so I need these panels to provide a good moisture barrier so my insulation won't get wet.

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    I&C Engineer (mostly WWTP) Lakee911's Avatar
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    I've used construction adhesive before. I like the polyurethane type.

    They make a special tape for tyvek-type insulation taping. I'd use that. It's thin, but stickier than all get out. It'll stick to it just fine.

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    DIY Senior Member Noth Jersey's Avatar
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    Most folks seem to use construction adhesive. Owens Corning recommends screwing furring strips into the preformed channels to hold the foam in place: http://www.youtube.com/watch?v=oNE1QQreOkA

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    Jack of all trades frenchie's Avatar
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    That's so they can sell you the pre-formed channelled foam panels.

    PL works fine.

    Spray foam doesn't eat the foam panels, but can bulge out & then you have to cut off the excess... pricey, too. But useful for filling the irrgular gaps if you had to cut around something.

    You'll need to cover the foam with sheetrock or wonderboard or something, otherwise you've got a serious fire hazard.
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    DIY Member export!'s Avatar
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    PL makes a foam board adhesive. Caulking tube. In Canada we use Tuck Tape to seal foam board, 6mil plastic, or house wrap. It sticks very well and maintains the vapour barrier for code.

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    DIY Senior Member dlarrivee's Avatar
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    Tape the seams with Tuck Tape:


    LePage has PL 300 which is meant for this exact application:



    You might want to test other types of adhesives that you plan to use, some of them could eat the foam. Foam in a can does a good job of adhering rigid foam to concrete as well, but it is expensive, so I'd only use that on any cutouts or spots where tape wont cut it.

    Please do not add another vapour barrier (or housewrap) on top of the foam, once you have taped all of the seams you will have created a barrier and adding another will just create a pocket to TRAP any possible moisture.

    How do you plan on air sealing, and insulating your rim joist between the floor joists?

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    DIY Senior Member dlarrivee's Avatar
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    Quote Originally Posted by frenchie View Post
    That's so they can sell you the pre-formed
    You'll need to cover the foam with sheetrock or wonderboard or something, otherwise you've got a serious fire hazard.
    This is true, you need to drywall over the studs and fibreglass when you're done.

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    Nuclear Engineer nukeman's Avatar
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    In my basement project, I am using 3/4" foamboad (XPS) attached with PL 300 and using Tyvek tape for the seams. I've found that you need to use about a tube of PL 300 per sheet of foamboad to get good coverage. I am also building a 2x4 wall in front and using unfaced batts so that the cavity can dry to the inside. For the rim joist, I am using 2" XPS and filling the rim joist cavities with R30 unfaced fiberglass for additional insulation and for a fire barrier.

    On my top plate, I am using 2x6 PT lumber. This is so the top plate will go over the foamboad to create a fire block. I used PT for the top plate as it rests on top of the cinderblock wall.

    I'm using PT 2x4 for the bottom plate and I am putting sill gasket material underneath it. This keep the PT from being in direct contact with the concrete and should extend the life of everything.

    For drywall, I am still deciding. I have looked at Georgia Pacific DensArmor Plus, but many places around here no longer carry it. Lowe's has 15 sheets left here, but no longer get any new stock. I also hear that it is really difficult stuff to work with.

    You're probably well on your way on the project already, but just wanted to let you know what has worked for me so far. Also, remember hozizontal fire blocking at 10' intervals and vertical fire blocking (usually the top plate, use fire blocking foam for cracks and holes for electrical/plumbing).

    Good luck.

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    Jack of all trades frenchie's Avatar
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    I LOVE watching engineers DIY.
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    Nuclear Engineer nukeman's Avatar
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    Quote Originally Posted by frenchie View Post
    I LOVE watching engineers DIY.

    Overkill, perhaps?

    I forgot to mention that I added horizontal blocking between all of the studs (eventhough they weren't needed). This way, I used up scraps, straightened out any studs that weren't straight, and sure made everything rigid as hell.

    Remember hot dipped galvanized nails for anything that touches the PT lumber. I used HDG nails everywhere so I didn't have to buy one type for PT lumber and another for non-PT lumber.

    I'm also a bit of a perfectionist when I make something. That plus the engineer side of me means that things take time to get done, but are also seriously overbuilt. You should see the deck I built. The ground will give away before the structure does. :lol:

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    DIY Senior Member Master Brian's Avatar
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    Quote Originally Posted by dlarrivee View Post
    How do you plan on air sealing, and insulating your rim joist between the floor joists?
    My thought was to buy a sheet of the pink rigid foam board and cut approx 7" x 16" pieces out and stick those into the space between the joists, rim joist and sill plate. I figure, which might change, that I'd stack enough to bring it close to flush with the new wall. I also thought about using some spray foam to seal the last piece to the joists, but not sure if that is a good idea or not. Don't want to trap moisture in the cavity.

    I may not have to buy a sheet, or two or three, I might have enough scrap left over from doing the walls. Just depends upon how it all lays out.

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    DIY Senior Member Master Brian's Avatar
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    These are my thoughts, which are subject to change. The framing is somewhat underway, but I'm not in a huge hurry....so feel free to correct me if an error is seen or a better method.

    Quote Originally Posted by nukeman View Post
    In my basement project, I am using 3/4" foamboad (XPS) attached with PL 300 and using Tyvek tape for the seams. I've found that you need to use about a tube of PL 300 per sheet of foamboad to get good coverage. I am also building a 2x4 wall in front and using unfaced batts so that the cavity can dry to the inside. For the rim joist, I am using 2" XPS and filling the rim joist cavities with R30 unfaced fiberglass for additional insulation and for a fire barrier.
    Thanks for the heads up on the glue and tape.

    As for the batts, I thought they weren't a good idea in the basement? With that said, I have been using them for a bit of sound deadening in interior walls, to block furnace/sump pump/laundry room sounds, and in the ceiling area, to block upstairs sounds and to keep sounds from basement in basement. I realize, it's not the best method, but it does help a little and for the price, it's been an easy solution.

    So you think on the interior side of the XPS, the batting is ok? I was planning on the thin stuff, comes in an accordian bundle and is used a lot under vinyl siding, and glueing that against the wall. Then over that, I was planning on building my walls. Then filling the wall cavities with 1-1/2" pink/blue rigid foam. I'm guessing it is the XPS stuff, but I'm not sure of the tech names. They sell the white and the blue or pink. I'm bad remembering names....


    Quote Originally Posted by nukeman View Post
    On my top plate, I am using 2x6 PT lumber. This is so the top plate will go over the foamboad to create a fire block. I used PT for the top plate as it rests on top of the cinderblock wall.

    I'm using PT 2x4 for the bottom plate and I am putting sill gasket material underneath it. This keep the PT from being in direct contact with the concrete and should extend the life of everything.
    Good idea on the top plate, but I don't believe that will work well for me. In fact, only two walls, might, get top plates. The rest are going to be somewhat scabbed into place. Sounds messy and half-assed, but it's what works and is somewhat necessary in several spots. I left the gasket material out from underneath, as I wanted an escape if any moisture should get under there. Hmm... Since this is an old house, I am matching the baseboard trim with the 1"x6" stuff in the rest of the house which allows me to keep the drywall off the floor almost 2".


    Quote Originally Posted by nukeman View Post
    For drywall, I am still deciding. I have looked at Georgia Pacific DensArmor Plus, but many places around here no longer carry it. Lowe's has 15 sheets left here, but no longer get any new stock. I also hear that it is really difficult stuff to work with.

    You're probably well on your way on the project already, but just wanted to let you know what has worked for me so far. Also, remember hozizontal fire blocking at 10' intervals and vertical fire blocking (usually the top plate, use fire blocking foam for cracks and holes for electrical/plumbing).

    Good luck.
    I've already decided for less than about $100 more I can get the unfaced mold/mildew resistant rock. Not sure who makes it, but it's sold locally at Lowes. It will go on all exterior surfaces and at the very least on the bottom few feet of the interior walls. I am debating on using it for the ceiling, especially below ductwork or water lines. Though all are insulated well, I don't want a future mold problem.

    Over the rock I will be installing a beadboard wainscot (sp?), not sure if panel or true tongue and groove pieces. Have to price it up. When I did my bath, there didn't appear to be much savings on the panel type and the T&G looks more authentic.

    I am well under way, unfortuneatly not with the insulating or framing, but moving some duct work, water lines, etc...

    As for fireblocking. I know, it's a good idea in theory, but it is not something I'm even worried about. If this were a newer house, I'd do it. Being as this house has relatively little, if any, is there really any point?

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    DIY Senior Member Master Brian's Avatar
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    Quote Originally Posted by nukeman View Post
    Remember hot dipped galvanized nails for anything that touches the PT lumber. I used HDG nails everywhere so I didn't have to buy one type for PT lumber and another for non-PT lumber.
    I will keep that in mind, but so far I have been using exterior grade decking screws for everything. My experience has been nails never drive well into the old joist material, even with a nail gun. Add to that, I don't want to create a lot of extra banging and chance knocking 100y/o plaster loose. I am also able to change my mind as I go and move studs around. Again, it's an added cost, but a minimal one.

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    DIY Senior Member dlarrivee's Avatar
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    Quote Originally Posted by Master Brian View Post
    My thought was to buy a sheet of the pink rigid foam board and cut approx 7" x 16" pieces out and stick those into the space between the joists, rim joist and sill plate. I figure, which might change, that I'd stack enough to bring it close to flush with the new wall. I also thought about using some spray foam to seal the last piece to the joists, but not sure if that is a good idea or not. Don't want to trap moisture in the cavity.

    I may not have to buy a sheet, or two or three, I might have enough scrap left over from doing the walls. Just depends upon how it all lays out.
    Wow...

    Okay. Just quickly, here if a joist is 16 ON CENTER then you subtract the width of one joist (1.5") you end up with 14.5" as a ROUGH cut... If that sounds odd to you, then you have a lot more learning to do before tackling this project.

    Nukeman, fibreglass does absolutely nothing to stop fire, and is absolutely useless as a fire barrier. Mineral fibre/rock wool is what you would require to do that.

  15. #15
    Nuclear Engineer nukeman's Avatar
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    To meet code, you need the vertical and horizontal fire blocking. This can be 2x material, drywall, etc. For the insulation, read this:

    http://www.buildingscience.com/docum...lation-systems

    If you have the XPS, it becomes a vapor barrier and prevents warm/moist air from condesing on the cool wall. It also slows vapor coming from the wall to the interior. Batts are okay in this situation..if you don't used faced insulation or put up a plastic barrier. Since the ground is basically always wet, you can't dry to the outside very well. So, insulation, drywall, and paint has to let the wall dry to the inside.

    Perhaps I shouldn't have said firebarrier. Drywall will be the actual ba9in the barrier in my situation. Vertical fireblocking done with the top plate. Hortizontal fireblocking can be done with a strip of drywall (or similar) every 10' pressed tightly to the XPS.

    It sounds like you can still get the drywall I was looking at. They stopped carrying around here. I asked a few other places about here and they look at you like you are crazy when you mention paperless drywall.
    Last edited by nukeman; 12-05-2009 at 07:03 AM.

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