XPS fastening to concrete walls

parker650December 28, 2010

I've got a 12 year old colonial with poured concrete foundation walls. I can already tell the walls aren't square and am not thrilled with the thought of using adhesive...

So, which of these would you recommend:

A. 1/4" Tapcons with washers


B. 1/2" x 3 3/4" concrete wedge anchors

Keep in mind that I have a hammer drill but it is a big old Milwaukee with 1/2" bits, so I'd most likely have to purchase a different (smaller) hammer drill just to use the tapcons. With the drill that I have I can install the wedge anchors no problem. Wedges are double the price but I won't need to buy another drill...

My concern is with the heat/cold conductivity of the larger anchor, could that cause any issues?

I'm thinking of anchoring each 4'x8' sheet of XPS with 2 anchors (midpoint at 2' and 6' up) then framing a wall up tight against it. Once I plum the wall I'll use wedges as needed to keep pressure on the XPS.

Any thoughts or recommendations???

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The wedge anchors are a waste of money for two pounds of XPS. I've used 1/4" concrete screws with fender washers.

Fender washer

Count on four-six fasteners for sheets that size. However, by drilling near the edge of a sheet, you can often overlap the washer onto the adjoining sheet as well, cutting down the number of anchors you have to use. Instead of fender washers, you may be able to use roofing washers, some of which come up to 3" in diameter. Also, tongue and groove (t&g) XPS will make for a tighter fit. Use handheld sprays where there are gaps. It doesn't have to be pretty; it has to be as airtight as possible.

The conductivity issue arises even with the 1/4" concrete screws. Before the drywall goes in and the space is heated, I've seen ice forming on the screws.

I use a half-inch hammer drill for 1/4 inch bits all the time. The more power, the better.

    Bookmark   December 28, 2010 at 6:34PM
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    Bookmark   May 2, 2013 at 10:52PM
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I'm using faster methods now. Such as plastic insulation anchors designed for percussion guns. Or just run a few furring boards over a wall of XPS

This post was edited by worthy on Fri, Jun 27, 14 at 17:19

    Bookmark   May 3, 2013 at 7:26PM
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Can you share why you're not using adhesive?

    Bookmark   June 26, 2014 at 11:45PM
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Poured walls are too irregular for the adhesive to hold. Plus mechanical anchoring pushes the board tight to the wall so the insulating board is more effective. Some jurisdictions may require mechanical adhesion.

    Bookmark   June 27, 2014 at 5:23PM
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