Attaching foam exterior concrete wall

10971 Views 7 Replies 4 Participants Last post by rustyjames, Apr 7, 2009

techinstructor

Discussion Starter · Apr 6, 2009 (Edited)

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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NJ Brickie

· #2 · Apr 6, 2009

I would be concerned will having a dryvit type material over foam at the base of my house. That area takes alot of abuse. Every stone your lawn mower shoots up will be a hole in the stucco. Don"t even think about running your weed wacker down the edge of your house. I would put the stucco right to the concrete above grade and forget the insulation on the outside above grade.

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NJ Brickie

· #5 · Apr 6, 2009

rustyjames said:
There are EIFS systems that are robust enough to deal with at grade issues such as stones, weed wackers, etc. There are also adhesives for gluing up the rigid foam. If it were me, I'd go with a few tapcons and washers too.

Yes there are. If they are placed on a suitable backing such as concrete, block, or brick. I have yet to see an EIFS system placed on foam that I couldn't easily puncture a hole in. EIFS manufactures state that foam should never be used below grade with their system. It creates an enviroment for all types of pests and bugs to live and breed. You will never know the problem exists because the exterior will look good. I stand by what I said. EIFS on foam over a house foundation is a bad idea period.

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