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Attaching foam exterior concrete wall

10938 Views 7 Replies 4 Participants Last post by  rustyjames
I am getting ready to insulate the exterior of my 10" poured concrete basement walls with 2" XPS rigid Styrofoam. The wall will be waterproofed with Bituthene sheet membrane above and below grade. The Styrofoam will not only insulate but will also serve as the protection board for the Bituthene. The above grade portions of the wall will be stuccoed with synthetic stucco.

The below grade portions of the foam will be held in place by the backfill. The above grade portions must be adhere with fasteners. All of the literature I've read about stucco recommends using Tapcons w/ washers that will fit flush against the foam. However, my contractor has suggested using a Ramset w/ washers, which I'm sure would be much faster and easier since the holes would not have to be predrilled. However, I'm not convinced that easier is always better.

I'm concerned about:

1) will the ramset nail be sufficient to secure the foam in the concrete and hold the weight of the board w/ m/l 1/4" of stucco on it?

2) can you ramset into the foam without destroying the foam?

My gut feeling is to go with the Tapcons as recommended but I would appreciate your recommendations here.
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I wouldn't use eifs down to grade either, but it sounds like he isnt. He's talking about rigid polystyrene, not the cured, white beaded board behind EIFS. I've only done the bagged, fibered plaster intended for polystyrene once, & I'm not sure why, but it actually does hold up IMO for some reason. I would see if you can get your hands on the plastic washers used for EIFS, as the washer closes over the screw head as you tighten them, & they "rough" so the plaster will stick. I've seen them sold with the tapcon already assembled from a insulation wholesaler.
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