Manufactured StoneNightmares

Without proper flashing, heavy-duty building paper, and

weep holes, walls behind cast-stone veneer can get wet

As a contractor specializing in reme-diation and repairs, I’ve been concen-trating for years on fixing failedapplications of EIFS and traditionalstucco. I’ve learned from experience thatmost stucco failures result from im-proper flashing and drainage detailsbehind the stucco. Typically, houses thatend up with rotten sheathing and fram-ing under the stucco don’t have properlyinstalled building papers and flashings.

In recent years, I’ve been finding

more and more cases of leaking and rotbehind another material that is verysimilar to stucco: cementitious manu-factured-stone veneer, or “cast stone,”as it is sometimes called. The problemswe are finding with cast stone are justlike the problems we’ve seen withincorrectly applied stucco. But the weather detailing flaws we identify inartificial-stone jobs often cause evengreater problems than the errors madewith stucco. With cast-stone veneer,

DECEMBER JLC 2004

by Dennis McCoy

Manufactured-StoneNightmares

Figure 1. Where stucco (top photos) andcast stone (bottom) have been installed onthe same home, the author frequently findsmore severe moisture and rot damageunder the cast-stone portions of the exte-rior. One reason is that the stucco termi-nates at the bottom with a weep screed,while the cast stone sits in a bed of mortarand grout, directly on a foundation ledge,with no weeps or flashings.

leaks and rot often show up sooner,progress more quickly, and cause moresevere damage inside the wall (seeFigure 1).

After investigating and repairing atleast a hundred examples, I’ve con-cluded that the problems with caststone go back to a misunderstandingof the material. Installers as well asbuilding inspectors have gotten usedto thinking of cast stone as a masonrymaterial, and they expect walls to getthe kind of weather detailing behindthe stone that is traditional with brick:a single layer of paper, lapped a coupleof inches at the horizontal joints. But,unlike brick, cast stone is not installedwith an air space between the claddingand the framed wall. Cast-stoneveneers are cementitiously adhered toa stuccolike base coat that is applieddirectly to the wall. Like stucco, caststone gets saturated with water in arainstorm and holds that water rightup against the framed wall. The papers

and flashings under the veneer have tofend off that moisture load withoutthe benefit of any drainage or dryingspace. One layer of paper isn’t going todo the job — two layers, as specifiedunder stucco, are necessary.

Painstaking Details RequiredIf anything, cast stone should in fact

be backed up by even tougher detailsthan stucco. That’s because it has somecharacteristics that may help create amore stressful moisture load for wallsduring wet weather.

For one thing, manufactured stone isa cement-based product that absorbsand holds water like stucco, but caststone is thicker than stucco and canthus store more moisture. Also, most ofthe cast-stone brands now have “ledge-stone” versions of the product, whichhave a long, horizontal shape; the long,flat, shelflike ledges are often slopedtoward the framing when installed,which provides a place for rain water

to puddle up and soak into the wall(Figure 2, next page).

The greater thickness of cast stonealso complicates the task of fabricatingand installing practical flashing com-ponents. The kickout or diverter flash-ing required where a roofline butts intoa wall is a good example. On job afterjob, my company gets paid goodmoney to go in after the fact, tear cast-stone veneer off a wall, and retrofit alarger kickout flashing to the wall be-cause the original roofer’s kickout flash-ing was too small to push water outbeyond the plane of the cladding. If thediverter flashing is too small, it may aswell not be there: All the water flowingand blowing against that spot will justget dumped into the wall system below(Figure 3, next page).

Of course, all the other typicalvulnerable spots in a stucco applicationare just as problematic, if not more so,in a cast-stone application. Windowpan flashings, for instance, are a good

DECEMBER JLC 2004

idea in a manufactured-stone job.However, we are more likely to see areverse-lap flashing error, with buildingpaper run to the window edge in sucha way that the window flange directswater beneath the paper instead of ontop of it (Figure 3). And, as with stucco,brick, or any other cladding, a cast-stone veneer should be equipped withweeps of some kind at any bottomtermination, whether at the founda-tion sill or above a window or abuttingroof. Otherwise, water will pool longestat the lowest points, and those areasmay stay continuously wet.

We also see problems when caststone is paired with another materialon the same wall. It’s very common, forinstance, for a single house to havestucco or EIFS as well as cast stone; ifthe joint where the two meet is detailedwrong, water can get to the wood-framed wall and cause trouble.

Investigating ProblemsWhen my company is called to look at

a building, the owners or the builderoften have no conception of the severityof the problem they may be facing. Polyvapor barriers under the home’s drywalloften conceal wall framing that issopping wet; on the exterior, the cemen-titious stone or stucco does not decay, soit never betrays the secret underneath.Homeowners may complain of just afew small leaks, or be worried about amoldy smell.

From experience, we know wheretrouble is likely to be found, and howbad it can be. By spraying a wall withwater while we create negative pressureinside the house, we can find out howwater is getting in, and by removing afew small sections of the cladding, wecan get an idea of the extent of theresultant damage.

Repairing the FailuresOn many occasions, our company has

found a shocking amount of water dam-age and rot under the cast-stone clad-ding of homes less than two years old, orin some cases less than one year old. Theamount of water that can be taken in

DECEMBER JLC 2004

Figure 2. Long, flat “ledgestone” pieces like this create many horizontal shelves wherewater can stand and soak into grout joints.

Figure 3. Undersized or omit-ted diverter — or kickout —flashings allow water to flowbeneath the cast-stone facade(above). Window flanges thatlap under instead of overbuilding paper can bring rainwater into direct contact withthe sheathing (right).

DECEMBER JLC 2004

Under a Fine Surface, a Disturbing Discovery. . .... and a Costly Repair

The owners of this one-year-old cus-tom home reported moldy smellsbehind the drywall; a mushroom grow-ing from the cast-stone veneer face wasthe only visible sign of trouble on theexterior . The gutter butting into thetop of the wall seemed a likely sourceof moisture, while the bottom of thewall provided no way for moisture toescape .3

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To repair the damage, the author’s crew replaced the rottedwood members , but was able to leave the original drywallin place because it had been protected by the interior vaporbarrier . Parts of the band joist were left in place but soakedwith a copper-based wood preservative .9

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Opening the wall revealed severely rotted OSB sheathing and damage to the framing. While the row of soldier bricks at fasciaheight provided some protection , the water coming off the roof saturated the cast stone and soaked through the housewrap beneath,turning the sheathing at the base of the wall to compost in less than two years .6

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On this job, the original installer of the cast-stone veneer wall hadtried unsuccessfully to stop leaks by spraying a clear sealer onto thestone and by removing the lowest courses to apply a membrane flash-ing where the wall meets the foundation. To assess the problem, theRam Builders team first seals large openings inside the home andsets up a blower door . With the blower door running to depres-surize the house, the crew turns on a water-spray apparatus , thussimulating the effect of a 15-mph wind-driven rain. Within a shorttime, water finds its way into the house .4

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Destructive Investigation: Tracing a Leak to Its Source

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After verifying that the cladding leaks, the team digs under the surface to find out why. Tearing off small areas of EIFS on the upper wall reveals that there is no building paper or window flashing installed where the EIFS meet the caststone , or between upper and lower win-dows in the EIFS wall . Tearing off caststone near a window , the team learnsthat water has wet the OSB sheathing. Theauthor measures high moisture contenteven at the bottom of the wall, where nodirect stream was applied . The retrofitflashing repair has proven ineffectivebecause flaws higher in the wall dumpwater behind it.

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Destructive Investigation (continued)

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and held by cultured stone is significant— enough to support robust growth ofwood-destroying funguses. If rot organ-isms have water and they have wood,they will thrive until the wood is gone.Often, what we find under cast stonelooks more like the ashes of a fire thanlike lumber (see “Under a Fine Surface, aDisturbing Discovery,” page 4).

If it’s caught soon enough, the dam-age can be repaired. But this is far morecostly than doing the job right the firsttime. Although I make my living fromthis kind of work, I wish that everybuilder and contractor who installs thismaterial, as well as the building officialswho inspect the jobs, could see some ofthe failures I have seen and learn how toavoid them. Too often, I’ve seen prob-lems like these ruin a family’s financeswhen they lead to the uninsured loss ofmuch of a home’s value.

Details That WorkCode provisions for cast stone can be

confusing and murky. The product isn’tmentioned in the body of the buildingcode, and the evaluation reports andmanufacturer instructions required forcode acceptance can be contradictory orincomplete. But the basic methods re-quired to succeed with the material are

not that complicated. In essence, caststone has to be treated as if it were stucco.

Before you apply lath to the wall, youneed to be sure you have a weather-resistant paper barrier on that wall —and it needs to include two layers ofpaper, not just one. Wherever there arepenetrations, or intersections betweenassemblies such as walls and roofs, orjoints between cast stone and othermaterials like brick or stucco, theremust be properly lapped flashings thatkeep kicking water away from thebuilding. And at the bottom of thewall, there has to be a way for water todrain out. If all those precautions areobserved, there is no reason cast stoneshould cause moisture problems.

When you’re choosing your buildingpaper, be careful. Type D paper gets a“minute rating,” based on the time thepaper can be placed in direct contactwith water before it soaks through. Youcan get 15-minute, 30-minute, or 60-minute rated paper, and the more se-vere the climate, the higher the ratingyou should choose. In dry and mildparts of Southern California or Arizona,for instance, two layers of 15-minutepaper ought to be fine. In the valley-floor areas near Salt Lake City, we usetwo layers of 30-minute paper. But if we

work up near the ski areas, where thereis lots of wind and rain, we use 60-minute paper. Sixty-minute paper isvery rugged stuff — it is more thantwice as thick as 30-minute paper. InHouston, we use either 60-minutepaper or sometimes a layer or two ofasphalt felt paper applied over the topof a housewrap such as Tyvek.

But no paper is intended to beabsolutely waterproof for an indefiniteperiod. That’s why the flashings andweeps are so important. If you don’thave them, water can pool at low pointsand stand against the wall for hours,days, or weeks. And if that happens, nopaper, be it housewrap, asphalt felt, orType D kraft, is going to save your wallfrom rot. So if you’re applying cast stone,be smart: Use the papers, install theflashings, and provide the weeps. It willcost a little more, but it is a lot cheaperthan hiring me and my crew to comeback and fix the wall when the studs aredecaying underneath the cast stone.

Dennis McCoy owns and operates RamBuilders, based in Lindon, Utah, whichspecializes in remediation and repair workin Utah, Texas, Colorado, and California.