Attaching metal lath over
concrete and foam insulation.

Ask the pros-August, 2005

By Reggie Bullard


Attaching metal lath over concrete and foam insulation.

This seems lke a good method, although I haven't tried it,
it was submitted by a reader, Michael Krall . Thanks Micheal.
It seems an excellent alternative to furring concrete or masonry first, before attaching 
the metal lath. These fasteners were made for EIFS, but are strong enough to work.
Care should be used to avoid embedding the lath into the foam,
preventing a key. Spacing should be an industry standard 12" oc,
horizontally and vertically.

 Micheal writes:
Non-conducting masonry anchors for foam board application:

This is the brand of fastener we are using. I talked with the tech. guy at Walrus 
and felt he was pretty knowledgeable.

There is data on foam over masonry in a couple of the articles here. Paul Fisette is a really sharp fellow. Used to moderate the building science forum at Journal of Light Construction.
Years ago, in the planning and how to do it stage, I had conversations with Paul about foam over Masonry.

What we are doing is attaching both foam and stucco wire (self furring, no paper backer) with the plastic anchors. I figured out that attaching the foam with the fasteners and then wiring the stucco wire to the fasteners was going to cause the wire to be too loose and too far away from the surface of the foam. The attachment schedule is 24" horizontal and 18" vertical with use of adhesive. That would switch to 12" vertical without adhesive. 

As an aside, there are a lot of adobe and rammed earth homes built in the southwest. Many of them have exterior insulation board with stucco over. Most of these buildings have the foam nailed on with double dip hot galvenized nails (thin shank types are better). 

I originally came across the concept of exterior insulation in the old passive solar books then cross referenced it to adobe/rammed earth (we built a passive solar adobe shop before we started the house). 

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