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Green Building Blog

Fiberglass Lath Works Better than Metal (and Won’t Rust)

Covering foam insulation on the outside of a foundation or exterior wall just got easier — and this product works for interior stucco features, too

SpiderLath stands proud of the felt. SpiderLath has foam-rubber furring strips that hold the lath off the wall. Mortar easily squeezes through the lath and locks into it with a solid grip.
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SpiderLath stands proud of the felt. SpiderLath has foam-rubber furring strips that hold the lath off the wall. Mortar easily squeezes through the lath and locks into it with a solid grip. It's flexible. SpiderLath easily conforms to interior or exterior corners. Galvanized or PVC expansion joint, corner bead, and drip screed can be used; on chimney boxes and interior details, these trim pieces can be omitted.
Image Credit: Michael Chandler
Installation is a breeze. Because of its light weight, SpiderLath can be installed with much less of a struggle than galvanized lath.
Image Credit: Michael Chandler
The carpenters — not the stucco contractors — perform the prep work. This job included window shade brackets. After the brackets were installed, they were carefully flashed.
Image Credit: Michael Chandler
Look, Ma — no hacked-up arms! Compared to prickly galvanized lath, SpiderLath is a pleasure to handle.
Image Credit: Michael Chandler
Integral gaskets. SpiderLath comes with foam-rubber furring strips that seal fastener penetrations.
Image Credit: SpiderLath

A shorter version of this article appeared in Fine Homebuilding
.

In order to provide a positive mechanical bond for exterior stucco and manufactured-stone veneer, builders install lath over felt paper or housewrap. But if you have ever worked with conventional galvanized expanded-metal lath, you know that the chore is anything but a pleasure. Metal lath is sold in large sheets that are sharp, prone to rust, and must be fastened through housewrap or felt paper in such a way that there’s a chance of water penetration. To me, the future of lath lies in products like SpiderLath.

I was first drawn to SpiderLath because it comes in a 4 ft. x 75 ft. roll that weighs only 25 lbs., and because the material has no sharp edges. That means I can lath a 25-ft.- tall chimney by climbing to the top, unrolling a 4-ft. x 25-ft. piece — which weighs only 7 lbs. — fasten it at the top, and then work my way down, without cutting up my arms in the process.

I was also pleased to learn some additional advantages of to this alternative material. SpiderLath has foam-rubber furring strips spaced 6 in. on-center; these strips not only hold the material off the wall — allowing mortar to squeeze through and get a good grip — but they seal every staple penetration through the felt paper or housewrap.

Made from alkaline-resistant fiberglass — coated to make it stiff and to protect the fibers from the abrasive elements in the stucco or stone adhesive — SpiderLath is actually stronger than expanded metal lath. It also can be cut with a utility knife or scissors, and though it is stiff enough to lie down smoothly it is still flexible enough to be easily folded around corners. Because it’s so easy to shape, we’ve recently used it for decorative stucco range hoods and interior fireplace surrounds. (Of course, there are a few tricks that you can do with galvanized lath — for example, crush it into a self-supporting three-dimensional shape — that you can’t do with fiberglass lath.)

I also like SpiderLath for its durability on the job site. Expanded-metal lath that sits around too long before being used always seems to get mangled into a crinkled mass of unusable rusty scrap metal. But other than the fact that the rubber furring strips get a little gummy when left in the sun, SpiderLath is pretty indestructible. I can keep a roll or two in the back of my trailer and cut off pieces as needed.

Fasten it with staples or roofing nails

Like galvanized lath, SpiderLath needs to be mechanically fastened 6 in. on center. We use galvanized roofing staples with a 1-in. crown and 1 ¼-in. leg or roofing nails. Since stucco expands and contracts at a different rate than the substrate, it’s a good idea to seal all penetrations. We use a Tyvek and a double layer of asphalt felt, and we install the SpiderLath with the rubber strips oriented vertically to allow moisture to drain to the weep screed at the bottom. On large projects, I use galvanized or PVC corner bead, drip screed, and expansion joints, but I omit these trim pieces on smaller jobs like chimneys and decorative interior stucco work.

On my jobs, the same carpenters who are responsible for the Tyvek, tape, flashings, and asphalt felt also install the lath, so the stucco crew just has to deal with the stucco. I think I get a better price when the stucco contractor’s scope of work is simplified, with no responsibility for the water-tightness of the system.

SpiderLath costs about the same as galvanized expanded-metal lath (about $0.50 per sq. ft.), but has to be ordered ahead of time from the manufacturer. (Some manufacturers also offer a more expensive type of non-metallic lath that isn’t mechanically fastened — it’s rolled into thinset over foam board. I priced this system for a recent job and, not counting the cost of the foam, it was 30% more expensive than the SpiderLath and two-coat type-S stucco system.)

—_Michael Chandler is a contributing editor and President of Chandler Design-Build, in Chapel Hill, NC_

4 Comments

  1. Jim Andersen | | #1

    SpiderLath
    Will this work screwed to Logix foundation for a "plaster" coat ???

  2. User avater
    Michael Chandler | | #2

    SpiderLath and Logix Insulating Concrete Forme
    Yes SpiderLath can be screwed to ICF's and have conventional stucco applied to it. I'm not sure how the price would work out but I think we did that on one job and ended up going back to roughing up the surface and applying two coats of surface bonding cement directly to the foam without reinforcement (beyond the fibers in the surface bonding cement) followed by a good elastomeric paint which ended up being very easy to repair and maintain and inexpensive to install.

    Spider lathe with real hard coat stucco would be more fire resistant and impact resistant but I would still give it a couple coats of good paint to seal it and let it shed water and dirt more easily.

  3. Kent Stumpe | | #3

    Fiberglass Lath
    BASF Wall Systems also offers a patented fiberglass lath. PermaLath® 1000 is listed in ESR 2429 and includes field mix C926 stucco or BASF StuccoBase. It has also been extensively evaluated by third party testing and an 18-month university study (University of Florida.) All testing and technical literature can be downloaded from http://www.permalath.basf.com.

  4. User avater
    Michael Chandler | | #4

    BASF
    I looked into the BASF product when we were building this house but couldn't afford it even with the homeowners employee discount.

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