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Musings of an Energy Nerd

Fasteners for Concrete and Brick

Advice for contractors installing rigid foam or furring strips to walls made of concrete, CMUs, or bricks

When installing furring strips and continuous insulation over a masonry wall or a concrete wall, contractors can choose from a variety of attachment methods, including concrete screws (Tapcons) or powder-actuated fasteners.
Image Credit: Image #1: Building Science Corporation

Builders who install rigid foam insulation need to know what type of fasteners to use for a variety of substrates. One challenging situation involves installing rigid foam or furring strips over concrete, as might happen when rigid foam is installed on the interior of a basement wall. But even builders who are familiar with fastening methods for concrete might wonder if the same techniques are appropriate for brick walls.

In this article, I’ll try to provide advice on the best mechanical fasteners for concrete, brick, or CMU (concrete masonry unit) walls. I’ll consider a variety of scenarios, including the attachment of furring strips directly to the wall, the attachment of rigid foam without furring strips, and the attachment of furring strips through a layer of rigid foam. I’ll also look at the best fasteners for OSB or plywood subfloor panels when the subfloor is installed over continuous rigid foam above a basement slab.

Types of fasteners

There are two basic types of fasteners for concrete and masonry:

Drilling a hole in concrete

If you’re using a fastener that requires a pre-drilled hole, you’ll need a hammer drill with a depth stop. (Although it’s possible to drill holes in concrete with an ordinary electric drill, the work is far faster with a hammer drill.) Use a high-quality bit designed for concrete.

In most cases, the hole needs to be 1/2 inch deeper than the fastener will penetrate. Once the hole has been drilled, use a turkey baster or a baby’s ear syringe (available at drug stores) to blow the dust out of the hole. It’s also possible to vacuum out the dust or to blow it out with an air compressor.

If you’re fastening furring strips…

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  1. user-7062640 | | #1

    mason jar lids or plywood as washers
    In the interior of my walkout basement I've been using foil faced polyiso, either 2 or 4 inches (2" below grade, 4" in walls above grade). Polyiso seems favorable from a greenhouse gas standpoint, has a high R per inch, and meets the flame and smoke rating requirements here for basement walls, so I can avoid covering it with drywall. I've been using either 3.5 or 6 inch tapcon screws because they're easy to find. Where I want to hang tools or protect the foil from wear, I'm using a plywood sheet essentially as the washer. In areas where that's not necessary, I used a mason jar lid plus a wide washer. These distribute the strength of the screw and are holding the polyiso sheets very tight. Here's a picture plus detail of both--plywood where the tools are, and just mason jar lids behind the built-in cabinet.
    -Shawn Salias

  2. Malcolm Taylor | | #2

    If you run out of mason jar lids, you can buy cap washers at most big box stores. They are about 20 bucks for 500.

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

    Response to Shawn (Comment #1)
    You wrote, "Polyiso ... meets the flame and smoke rating requirements here for basement walls."

    You may be accurately reporting the interpretation of your local code official. But most code officials won't allow foil-faced polysio to be left exposed, because it's a fire hazard. Rigid foam needs to be protected by a layer of 1/2-inch drywall.

    The exception is a brand of polyiso called Thermax -- a special type of polyiso that has passed fire safety tests. (I think there is at least one other brand of polyiso that has successfully completed Thermax-type testing and approval, but I forget its name.)

    So most common brands of polyso need to be protected with drywall.

    Malcolm makes a good point. Foam fastener washers (which I mentioned in my article) cost about 4 cents apiece, whereas mason jar lids cost 18 cents each at WalMart.

    Of course, if you are talking about used lids, they're free (assuming you do a lot of canning, and you've been saving your used lids). Remember, though, there there may be a better way to use these lids. If you open your mason jars carefully, the lids can be re-used for your next canning job. That's what I do.

  4. Kohta Ueno | | #4

    Hammer-Set Fastener Options

    Like concrete screws, hammer-set fasteners require a predrilled hole. Hammer-set fasteners are surrounded by an expandable sleeve. Once the fastener is inserted into the drilled hole, the installer drives the fastener home with an ordinary hammer, and the sleeve expands.

    One popular brand of hammer-set fasteners is Red Head. The maximum available length of these fasteners is 2 inches, so they generally aren’t used for rigid foam.

    As an FYI, 3 inch lead and plastic tap-in/hammer in anchors are available; I have successfully used them to install 2 inches of foam to my basement walls. I used plastic washers (had to be drilled out for the 1/4" diameter fastener) to prevent pull-through of the fastener. The hammer-in fasteners had intermittent problems expanding due to the "bounce" of hammering through foam; I found that I had to "pre-expand" the fastener slightly to get it to work.

    All this being said--if I had to do this all over, I'd just buy the Rodenhouse fasteners.

    Mushroom Head Nail In Anchor Nylon 1/4 x 3 (Box of 100) weight 2.25 Lbs

    1 3/4" Foam Fastener Washers, 100 Count

    Also, for reference, this is how Joe's dad solved the problem:

    BSI-065: But I Was So Much Younger Then (I'm So Much Older Than That Now)*

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

    Response to Kohta Ueno
    Thanks for sharing your tips and experience.

    If GBA readers are curious about Joe Lstiburek's father's home-brew masonry fastener, the relevant information is reproduced below.

    Joe Lstiburek wrote:

    "How to attach 8 inches of foam insulation to the outside of a block wall? ... Time to go see Dad. ... After about an hour he got up without saying a thing and I followed him to the car and we drove to Canadian Tire. He got a long masonry drill bit, some gutter nails, a bunch of really big washers and some lead plugs. He sketched out the solution on a pad of paper. ... Worked like a charm.

    "[Caption to image] Dad’s Fastener - Gutter nails, a bunch of really big washers and some lead plugs. Put the nail through the washer. Push the lead plug onto the end of the nail. Lean the rigid foam against a masonry wall. Drill through the foam with a 5/8-inch diameter long masonry bit 1-inch into the masonry wall. Pull the bit out of the opening. Insert the fastener through the foam 'pilot' hole so the lead plug engages the hole in the masonry. Use a mallet to hammer the fastener home."


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