Metal Lath Testing

[Bud Rutherford]

Has diamond mesh metal lath ever been tested on vertical walls, either paper-backed or pre-papered walls, for water intrusion?

Every project that I have visited, after close inspection to the fastening devices (screws, nails, or staples), I have found that the fastener forces the metal lath through the water barrier. It is difficult to see the slits made in the paper unless you remove the lath.

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[Jerry Peck]

Has diamond mesh metal lath ever been tested on vertical walls, either paper-backed or pre-papered walls, for water intrusion?

Sounds like every project you have seen is doing it wrong.

Not because of the fastening (although that is typically done wrong too), but regarding what you described:

"paper-backed or pre-papered walls"

The correct way is to install a WRB (weather resisting barrier), then paper-backed metal lath. Felt building paper does not make an effective WRB.

One could (but it would be a lot more trouble to do) install a WRB, then wrap it with felt paper, then install plain metal lath over that.

Both of the above methods, WRB with paper-backed metal lath, and WRB with paper with metal lath, provide a bond breaker and a drainage plane.

The paper of the paper-backed metal lath serves as a bond breaker to keep the stucco from bonding to the WRB, that is its purpose, it is NOT the required drainage plane. The paper over the WRB serves the same purpose, then the plain metal lath is installed.

If you are only seeing paper-backed metal lath applied directly over the sheathing, that is the wrong to install it, there is no drainage plane - well, there is a drainage plane, but that becomes the wood sheathing, and we all know what is going to happen when you drain water down wood sheathing ... right?

Regarding the fasteners penetrating through the paper of the paper-backed metal lath, yeah, it has to. They also penetrate through the WRB, they have to, otherwise how is it held in place.

The same problem goes with the fasteners which secure the WRB in place.

However, the intent and design is to allow for drainage down the back of the paper of the paper-back metal lath (or down the face of the WRB as they are in intermittent contact with each other).

To directly answer your question though, yes, and water goes through stucco, water goes through the metal lath, and water goes through the paper bond break. That water then drains down the drainage plane. That is the concept and design of that system.

[Ted Menelly]

I think he meant break penetrating was it tears the felt. Tyvek or typical barrier does not tear as easy as the felt will so it is more than likely only the nail head penetration. I see folks using roofing nail guns set to sink deep ad tears things up. they should be nailing it on not smashing it in. Jerry is absolutely right in the proper way to apply the system. No WRB is rot in the waiting.

[A.D. Miller]

Felt building paper does not make an effective WRB.

JP: And you base this opinion on what? Not effective compared to what?

Aaron

[Ted Menelly]

Felt paper is exactly that, paper. Impregnated with tar or not it still absorbs water and wets the OSB or plwood slowly rotting it. WRB lets the wood breath but does not allow water thru to the sheathing.

[Jerry Peck]

JP: And you base this opinion on what?

WRB is typically used to refer to "weather resisting barrier" and "water-resistive barrier", which are frequently used interchangeably. "Weather resisting barrier" came about first, then it was changed to "water-resisting barrier", both referring to the same intended use. I do, though, need to get in the habit of using the current reference name of "water-resistive barrier" for greater accuracy.

From the 2006 IRC.

- WATER-RESISTIVE BARRIER.

A material behind an exterior wall covering that is intended to resist liquid water that has penetrated behind the exterior covering from further intruding into the exterior wall assembly.

Building felt does not provide that barrier.

From many of the sources I have read to having heard Dr. Joe as several seminars.

Not effective compared to what?

Tyvek

Typar

and others like them

Here is one such source: Housewraps, Felt Paper and Weather Penetration Barriers - Publications - BM&WT - UMass Amherst

This is from that source:
Scroll down to the section with the heading "Apples to Oranges", 3rd paragraph.
"A problem with the boat test is that water vapor can also trigger the indicator's change of color -- meaning that a highly vapor-permeable wrap like Tyvek fails. As an alternative, DuPont put Tyvek through AATCC 127, the "hydro-head" test, to prove its water resistance. In this test, the material is subjected to a 22-inch column of water -- the same force exerted by a 200-mph -- and must not leak a drop for 5 hours. This is a far more demanding test for water resistance than the boat test, yet as far as I know, among the plastic wraps, only Tyvek and R-Wrap have passed. Some researchers claim that felt has also passed, though inconsistently."

[A.D. Miller]

WRB is typically used to refer to "weather resisting barrier" and "water-resistive barrier", which are frequently used interchangeably. "Weather resisting barrier" came about first, then it was changed to "water-resisting barrier", both referring to the same intended use. I do, though, need to get in the habit of using the current reference name of "water-resistive barrier" for greater accuracy.

From the 2006 IRC.

- WATER-RESISTIVE BARRIER.

A material behind an exterior wall covering that is intended to resist liquid water that has penetrated behind the exterior covering from further intruding into the exterior wall assembly.

Building felt does not provide that barrier.

From many of the sources I have read to having heard Dr. Joe as several seminars.



Tyvek

Typar

and others like them

Here is one such source: Housewraps, Felt Paper and Weather Penetration Barriers - Publications - BM&WT - UMass Amherst

This is from that source:
Scroll down to the section with the heading "Apples to Oranges", 3rd paragraph.
"A problem with the boat test is that water vapor can also trigger the indicator's change of color -- meaning that a highly vapor-permeable wrap like Tyvek fails. As an alternative, DuPont put Tyvek through AATCC 127, the "hydro-head" test, to prove its water resistance. In this test, the material is subjected to a 22-inch column of water -- the same force exerted by a 200-mph -- and must not leak a drop for 5 hours. This is a far more demanding test for water resistance than the boat test, yet as far as I know, among the plastic wraps, only Tyvek and R-Wrap have passed. Some researchers claim that felt has also passed, though inconsistently."

JP: I'm familiar with the article. And from it:

"Housewrap or Felt?
Based on our testing, if I were buying a housewrap today, I would choose either Tyvek or R-Wrap, because they display the best water resistance. But so far, I've avoided the million dollar question - housewrap or felt? The truth is, there's not million dollar answer. In general, I don't think it matters a whole lot. If you get the flashing details right, and are careful installing the building paper, you will prevent 99% of the moisture problems caused by wind-driven rain and snow. Either product, housewrap or felt, will provide an adequate secondary drainage plane. And either product is permeable enough to allow interior moisture to escape.
As it happens, I have felt paper on my own home, and if I could choose between felt and housewrap and do it over again, I'd still choose felt. That's because I believe that under certain circumstances, felt outperforms housewrap. For example, an ice dam or roof leak may allow liquid water to get behind the felt or housewrap. It's also possible for the sun's heat to drive water vapor through the housewrap from the outside, where it can condense on the sheathing. In either of these cases, you now have liquid water on the wrong side of the wrap. Under these conditions, the liquid water would be trapped by the housewrap, which is permeable only to water vapor. Felt, on the other hand, will absorb the water, and more quickly dry to the outside."

It has been my experience that a single layer of 15lb felt is inadequate. But who is to say that it is inferior to housewrap? I have seen degradation of both behind several differ enc claddings over the years. Though it is a more recent player to the game, I have seen more housewrap failures in forensic inspections that I have for felt paper.

When I was building - back in the stone ages - we used two layers of 15lb. felt with staggered laps or 30lb felt. I've never had a callback based upon the WRB we used.

Aaron

[Jerry Peck]

JP: I'm familiar with the article. And from it:

"Housewrap or Felt?

I read that part to, but (from the part I posted - underlining and red text are mine)

"As an alternative, DuPont put Tyvek through AATCC 127, the "hydro-head" test, to prove its water resistance. In this test, the material is subjected to a 22-inch column of water -- the same force exerted by a 200-mph -- and must not leak a drop for 5 hours."

That is a lot more "real life" resistance that the other tests described, and "real life" is where it is installed, and where you want it to perform ... under wind driven rain conditions.

If Tyvek can resist an equivalent wind pressure of 200 mph for 5 hours without a drop leaking through, then think how it can perform when installed behind a protective cladding such as stucco, HardiePlank, etc., which takes the brunt of the wind drive rain force, allowing less pressure and water to reach the Tyvek to start with (I don't know how much less "pressure", but definitely a lot less "water" hitting the Tyvek).

[A.D. Miller]

That is a lot more "real life" resistance that the other tests described, and "real life" is where it is installed, and where you want it to perform ... under wind driven rain conditions.

Maybe. I wasn't there.

If Tyvek can resist an equivalent wind pressure of 200 mph for 5 hours without a drop leaking through, then think how it can perform when installed behind a protective cladding such as stucco, HardiePlank, etc., which takes the brunt of the wind drive rain force, allowing less pressure and water to reach the Tyvek to start with (I don't know how much less "pressure", but definitely a lot less "water" hitting the Tyvek).

Granted, but how does that make it superior to 30lb. felt? We don't know because of the built-in limitations of the testing criteria. And, we don't know who funded this testing, etc.

My point is that redundant systems are likely superior to any one single application of anything. At least they are in my experience.

Besides, it's all moot, if you consider that in the case of housewrap behind brick veneer, you are installing a 100-year cladding over 25-year wall ties and 50-year WRB. How does that make sense?

[Jerry Peck]

Granted, but how does that make it superior to 30lb. felt?

Where did 30# felt come from? Most who would cheap-out using felt would use 15# felt.

My point is that redundant systems are likely superior to any one single application of anything. At least they are in my experience.

Not understanding you there, one system is house wrap then paper backed metal lath, the other (from you) is 30# felt then paper backed metal lath ... both only have one layer over the sheathing and one bond breaker layer ... so where do you come up with "redundant", indicating 'more than one'?

Besides, it's all moot, if you consider that in the case of housewrap behind brick veneer, you are installing a 100-year cladding over 25-year wall ties and 50-year WRB. How does that make sense?

Better than "installing a 100-year cladding over 25-year wall ties and torn-on-installation 15# felt", right?

Yes, I know what you are saying, it like installing slate roof tiles over 15# felt ... Huh??? Makes no sense, but it is done.

Or how about concrete tiles installed as a System One roof system, where the concrete tiles will last 100 years and the System One roof system will last, if you are lucky, 10 years ... where is the sense in that?

[A.D. Miller]

Where did 30# felt come from? Most who would cheap-out using felt would use 15# felt.

True.

Not understanding you there, ... so where do you come up with "redundant", indicating 'more than one'?

What I meant was, yes, more than one layer of 15lb. felt.

Yes, I know what you are saying, it like installing slate roof tiles over 15# felt ... Huh??? Makes no sense, but it is done.

Or how about concrete tiles installed as a System One roof system, where the concrete tiles will last 100 years and the System One roof system will last, if you are lucky, 10 years ... where is the sense in that?

Who said this stuff was supposed to make any sense?

[Jerry Peck]

What I meant was, yes, more than one layer of 15lb. felt.

To clarify, you are saying TWO layers of 15# felt wrapped around the house AND the paper on the paper-backed metal lath?

[A.D. Miller]

To clarify, you are saying TWO layers of 15# felt wrapped around the house AND the paper on the paper-backed metal lath?

JP: Maybe. We always used 30lb felt and lath for stucco and two layers of 15lb felt for brick or siding.

[Jerry Peck]

JP: Maybe. We always used 30lb felt and lath for stucco ...

You lost your drainage plane with just one layer of 30# felt and lath (unless you still used paper-backed lath).

Which brings up a point to the original question:
- The *lath* is required to be secured to the framing/sheathing, *not the paper*. If the nails/staples/screws are through the paper and not holding the lath, yeah, they will tear the paper, but that it not the problem, the problem would then be that *the lath* would not be attached as required.

[A.D. Miller]

You lost your drainage plane with just one layer of 30# felt and lath (unless you still used paper-backed lath).

Which brings up a point to the original question:
- The *lath* is required to be secured to the framing/sheathing, *not the paper*. If the nails/staples/screws are through the paper and not holding the lath, yeah, they will tear the paper, but that it not the problem, the problem would then be that *the lath* would not be attached as required.

JP: This is, after all, last time I checked, a perfect world - right?

[John Carroll]

First off, welcome to my world, AD. JP tends to get off on strict interpretation of data, getting lost on the details.
Your point on the proper detailing around penetrations and terminations is the salient point in the debate of felt vs tyvek. All the "water resistance" in the world proves to be a very bad thing when water gets behind the WRB. And the most likely point of intrusion is at these areas where two different products come together.
Rainfall amounts and frequency matter also, what works in a dry climate would prove disasterous in a wet one. Felt has always proven a better choice for infrequent wetting due to its' ability to wick moisture from either side of the wall, tyvek fails miserably in that area. Given enough time between soakings water will eventually escape a felt covered wall. Not so a tyvek covered one. water behind tyvek immediately begins attacking the substrate, and continues until drying out, unless it is used in a wet climate, where it never dries out and the damage continues unabated. Multiple layers and bond reakers may be helpful, but in the end, if water is trapped, the damage will be worse.
They used to require cork or rubber washers on all fasteners to furr out the lath, and this also had the added effect of protecting the paper or felt from tears and overtightening of the screw or nail. but you don't see that much anymore with the advent of self furred lath, still a good idea tho...

[A.D. Miller]

First off, welcome to my world, AD. JP tends to get off on strict interpretation of data, getting lost on the details.
Your point on the proper detailing around penetrations and terminations is the salient point in the debate of felt vs tyvek. All the "water resistance" in the world proves to be a very bad thing when water gets behind the WRB. And the most likely point of intrusion is at these areas where two different products come together.
Rainfall amounts and frequency matter also, what works in a dry climate would prove disasterous in a wet one. Felt has always proven a better choice for infrequent wetting due to its' ability to wick moisture from either side of the wall, tyvek fails miserably in that area. Given enough time between soakings water will eventually escape a felt covered wall. Not so a tyvek covered one. water behind tyvek immediately begins attacking the substrate, and continues until drying out, unless it is used in a wet climate, where it never dries out and the damage continues unabated. Multiple layers and bond reakers may be helpful, but in the end, if water is trapped, the damage will be worse.
They used to require cork or rubber washers on all fasteners to furr out the lath, and this also had the added effect of protecting the paper or felt from tears and overtightening of the screw or nail. but you don't see that much anymore with the advent of self furred lath, still a good idea tho...

John: Agreed.

Aaron

[Stephen Meyer]

Tyvek drainage system?

[Jerry Peck]

Stephen,

Yes and no.

See those long wrinkles in the Tyvek? Those are intended to provided drainage channels, thus they should be installed vertically (like the piece on the right side of the window opening) and not horizontally (like the piece under the window opening).

However, what is missing (may be planned for and just not installed at this point) is the sealing tape which is placed over the joints/laps so seal it all up.

Over that would go the flashing (also not installed yet).

[Stephen Meyer]

Posted the photo on new construction of a hotel. I am a 3rd party eifs inspector and thought I would get some comments. You are correct with your assessment. Tyvek has a good set of install guidelines for their various products. I work with the south Texas Tyvek division quite often.

Thanks for the note.

sm

[Stephen Meyer]

Here is the link for testing of WRB.

Criteria List

sm

[Bud Rutherford]

The orginal question about testing revolved around the problems one faces when using metal lath and its installation against the WRB, whether it is paper, felt paper, or a housewrap.

Of course, the lath has to be fastened to the framing, that's a given, but what about the penetrations caused by the metal lath rubbing into the WRB itself? Fastener penetrations occur, but so do pentrations from the metal lath being screwed or stapled too aggressively into the framing. Fastener penetrations can be sealed, yes, but what about these other types of penetrations?

Would any of you see it as a greater benefit to use welded or woven wire instead of metal lath for a plaster application? Just as John Carroll pointed out there are Furring Nails and Furring Screws on the market. The Furring Wads hold the wire away from the paper or WRB for proper embedment, while at the same time sealing the puncture made by the screw itself. Also, the welded or woven wire does not have the sharp edge to it like metal lath does and this would reduce additional punctures to the WRB.

[Jerry Peck]

but what about the penetrations caused by the metal lath rubbing into the WRB itself?

The metal lath should not be in contact with the WRB, the metal lath should be separated from the WRB by the bond breaker layer (the paper of paper backed metal lath, or a layer of building paper over the WRB).

Would any of you see it as a greater benefit to use welded or woven wire instead of metal lath for a plaster application?

The metal lath is configured to hold the stucco in place better by its simple design of having "cups" which allow the stucco to 'grip' (be keyed over) and to 'support' the stucco and keep it from 'sliding' off the metal lath.

[Stephen Meyer]

Jerry is on top of his game......Here is a good note on Stucco in the coastal areas from cement.org

Q: Is stucco suited for use in a coastal environment? A: Portland cement plaster is suited to virtually every type of climate, whether wet or dry and hot or cold. It is popular in coastal environments because it is unaffected by moisture, but when metal lath is part of the system, there are potential concerns due to the elevated chloride levels in the environment.
Applying stucco over metal lath. In coastal areas, air is literally salty: it carries chlorides. This is an aggressive ion that corrodes metal. Hardened plaster is not affected by chlorides. If the plaster is direct-applied to concrete or masonry backup, there is little or no metal reinforcement in the plaster. If a 3-coat system is installed, whether the backup is frame construction or to achieve mechanical bond over a solid substrate, metal lath is attached to structural supports to hold the plaster to the wall. The lath is required to be galvanized, and embedding it in a highly alkaline environment like portland cement plaster provides added protection from corrosion. The lath should be fully embedded by the first base coat, called the scratch coat. This assures that the lath will have at least ½ in. (12.5 mm) of cover—the second base coat, a 3/8 in. (9.5 mm) thick layer, plus the finish coat at 1/8 in. (3 mm).
The combination of galvanized coating and plaster cover protects the metal. This makes it critical to minimize cracking of the plaster, which would otherwise provide a direct path for chlorides to reach the steel. Methods to minimize cracking include proper consolidation during installation, appropriate contraction joint spacing and proper curing of the freshly placed stucco material.
There are other protective measures that can be taken in extreme exposures. These include stainless steel lath, which is more resistant to corrosion due to chlorides, and polyvinyl chloride (PVC) lath, which is not susceptible to corrosion, but does not have the same strength or thermal coefficient of expansion as steel, and may not bond well to plaster.


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