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Drainage Plane Behind Stone Veneer


Jim Katen
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A local builder has begun installing stone veneer over a drainage plane. Starting with the wall sheathing, the application is thus:

Tyvek installed over the wall sheathing.

A poly drain board with vertical ribs is attached to the sheathing.

Fine poly mesh is applied over the drain board.

Expanded metal lath is secured on top of the mesh.

Scratch coat applied over the lath.

Stones embedded in mortar over the scratch coat.

They run the stone right down to paved surfaces and install ribbed plastic weeps at the joint. They also use these weeps above windows & doors.

In some places, they run the stone into the earth.

Has anyone seen this type of stone installation before?

I like the idea, but I have serious reservations about some of the details.

- Jim Katen, Oregon

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Hi Jim,

Except for running the stuff into the dirt, that looks kind of sweet. I suppose if it were cast river rock type stone that's grouted and wiped so that a lot of water can't pass through it you'll not see much water coming out of that screed. However, if it's that flat, ungrouted stuff I should think there'd be a lot of water.

Then there's the question of pests. Cover the bottom of that with earth and you've basically installed a little humidifier along the bottom of the wall to send evaporation up behind that poly drainage mat and have to hope that the tyvek will keep it out when it condenses.

Seems like it would make more sense to place a moat of stone around the base of the wall that will allow water to drain clear and air to circulate into there and keep things dry.

ONE TEAM - ONE FIGHT!!!

Mike

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Hi Jim,

Except for running the stuff into the dirt, that looks kine of sweet. I suppose if it were cast river rock type stone that's grouted and wiped so that a lot of water can't pass through it you'll not see much water coming out of that screed. However, if it's that flat, ungrouted stuff I should think there'd be a lot of water.

Then there's the question of pests. Cover the bottom of that with earth and you've basically installed a little humidifier along the bottom of the wall to send evaporation up behind that poly drainage mat and have to hope that the tyvek will keep it out when it condenses.

Seems like it would make more sense to place a moat of stone around the base of the wall that will allow water to drain clear and air to circulate into there and keep things dry.

ONE TEAM - ONE FIGHT!!!

Mike

The stone moat would help, but you'd still have hundreds of little poly termite highways running up the wall.

I still say terminate the stone above grade with a weep screed.

Download Attachment: icon_photo.gif Stone into soil.JPG

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Download Attachment: icon_photo.gif Weeps at concrete.JPG

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Download Attachment: icon_photo.gif Weep at window.JPG

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- Jim Katen, Oregon

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Hi,

Yeah, after seeing those, I think you're right and that's going to be pretty damp.

That's the problem with that stuff. In order for it to drain, you've got to get it above adjacent surfaces and keep it clear and who the hell ever heard of starting a stone wall two inches off the ground when it's supposed to look like it's supporting the wall?

Oh well, at least with the weep screeds they're trying.

Do you get subs down there? We generally don't see them north of West Seattle and for some reason only see a few outside of west Seattle. I think it's got something to do with not having the right kind of travel documents or something. We see Pacific dampwoods everywhere though.

ONE TEAM - ONE FIGHT!!!

Mike

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Mike-- yes active subs last week........... (rare though).

Jim, I would be concerned with that installation for the reasons already provided; what's the difference between that installation and brick veneer regarding termite concerns?

They have weeps, did they install any flashing?

Is that true stone, or cultured (looks like/ installed like cultured, but you are usually very precise with your wording)?

Do you guy's ever sleep?

Here's some CAD drawings from one manufacturer of the drainage mat (stuco- flex). It's in .dwg format, so I can't open them to check them out: http://www.stucoflex.com/details_drawings.htm

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I've never seen any faux stone installed like that -- or recommended to be installed like that -- so I can't say it is or isn't per the manufacturer's recommendations. While I give the builder credit for recognizing a potential moisture problem, I would have concerns about the stability of the stone applied over the plastic layers. I can't tell how thick the scratch coat is, or how rigid the plastic components are, so I'd question whether the stone will want to move around on top of a (possibly) flexy plastic substrate. Obviously, if it moves around much there is the prospect of it coming loose, but also the potential that cracks will develop in the mortar joints that would test the effectiveness of the drainage plane.

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There's been debate about whether the poly mesh is a good thing or not; the physics are iffy. I would like to see some Joe L. type studies comparing it's performance to other systems.

Chris, Oregon

Interesting. I'm not familiar with the poly mesh. It would seem that would be a good thing, but I guess we can't know without more study.

Other than the mesh, do you see anything you'd disagree with?

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I never see that much drainage consideration. Typically there are two layers of 30# felt between the tyvek and the metal lath. One of the better builders I know adds another layer of tyvek under the felt. The last job I saw being installed, the base layers for the stone were lapped about a 1/2" below the sill onto the stemwall. Another very good builder I know slaps this stuff over two layers of tyvek, he just doesn't get how much water is going to get behind this stuff. The rest of his details are top notch.

Asthetically correct job, but I think your concerns are right on the money.

Tom

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If the weeps are embedded in dirt, a concern is that they would clog/silt in over time. The underground stone and mortar could transpire water vapor and condense behind the stone. The water may not be able to get out. Freeze thaw cycles could cause the stone to pop.

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Joe L. concluded that for stucco two layers of building paper work fine as well as does a single layer of building paper over drainwrap. What didn't work was stucco directly over plastic wrap, which they have done alot around here.

So what's the added benefit of the polymesh? The controversy is over using it in an attempt to make a rain screen wall, which Jim's example is not.

In Jim's example I think it's waste and not good building science if he's installing the lath on top of the mesh. What you are doing is guaranteeing leaks (bulk water) into the cavity with the mesh. Why would you want to do that? You want to try and keep as much moisture out of the cavity as you can as there are just to many unknowns (adequacy of the weeps, increase moisture source for solar vapor drive, etc.).

I think two layers of 60 minute paper should do the trick on a rain hammered south wall in these parts.

Chris, Oregon

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Mike-- yes active subs last week........... (rare though).

Jim, I would be concerned with that installation for the reasons already provided; what's the difference between that installation and brick veneer regarding termite concerns?

With brick veneer, you've got (in theory) solidly grouted brick at ground level. With this installation, the little ribbed tunnels extend right into the soil. There's a potential for termites with both -- and I've found serious termite infestations behind brick veneer.

They have weeps, did they install any flashing?

The weeps work in concert with flashing above the windows. There's no flashing at the ground level.

Is that true stone, or cultured (looks like/ installed like cultured, but you are usually very precise with your wording)?

It's cultured stone. I was having an imprecise day.

Do you guy's ever sleep?

Gave it up for Lent.

Here's some CAD drawings from one manufacturer of the drainage mat (stuco- flex). It's in .dwg format, so I can't open them to check them out: http://www.stucoflex.com/details_drawings.htm

I can't open them either. I used to have a .dwg reader but it got lost in the last computer switchover.

- Jim Katen, Oregon

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http://www.culturedstone.com/

This is the document I used to start with as a basis for a consult I did for a problematic stone install.

the PDF is of the resultant article I wrote and was published in the Dec issue of the JLC

Here is a copy of the email I received from Joe S regarding the the article

Nice case study. I thought you got it all bang on. Some folks are being even more conservative out on the east coast by installing a 3/8 inch polypropylene mesh spacer like "Home Slicker" by Benjamin Obdyke between the primary drainage plane and the exterior building paper bond break to increase drainage and to promote some back ventilation.

Joe

Mark Parlee

Download Attachment: icon_adobe.gif JLC cultured stone dec08 from web.pdf

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  • 1 year later...

Old post but I'm wondering...The picture I saw didn't show the actual construction done. Why is it assumed the mason extended the drain mat into the ground? I'm not a mason by trade but, couldn't the drain mat stop at the sill? If the sill plate is recessed off the foundation face by 3/4", that would allow you to compensate for sheathing and a drain mat right at the sill/stem wall/foundation transition. With proper flashing and weeps at that point, the mason could have floated a scratch coat over the transition and set stone all the way to grade with a thinset or mortar. No drainage would be needed on the stem wall behind the veneer. Properly done, I don't see how stone down to grade would be a problem. I wouldn't run a fake stone to grade for capillary effect but natural stone would be fine I think.

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Old post but I'm wondering...The picture I saw didn't show the actual construction done. Why is it assumed the mason extended the drain mat into the ground? I'm not a mason by trade but, couldn't the drain mat stop at the sill? If the sill plate is recessed off the foundation face by 3/4", that would allow you to compensate for sheathing and a drain mat right at the sill/stem wall/foundation transition. With proper flashing and weeps at that point, the mason could have floated a scratch coat over the transition and set stone all the way to grade with a thinset or mortar. No drainage would be needed on the stem wall behind the veneer. Properly done, I don't see how stone down to grade would be a problem. I wouldn't run a fake stone to grade for capillary effect but natural stone would be fine I think.

Yes, it could have been done that way. In fact that's almost how brick veneer is supposed to be done. (In brick veneer, the flashing & weeps occur at the first course above grade, not at the transition from wood framing to concrete stemwall.) However, that is not what was done. If it were, we would see the flashing and weeps.

So if you wanted to do a wall like that, how would you install the flashing across the irregular mortar joints? In brick veneer, you have nice horizontal joints that can discreetly accommodate flashing. How would that work with stone?

-Jim Katen, Oregon

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  • 3 months later...

Perhaps a drain tile or pipe beneath it where it weeps down into? Magic invisible flashing perhaps? Careless installer? I don't know. Good point.

One of those pictures looks like there is a weep over the top of a window. That can't be right can it? That seems sloppy and like a built in window washing chore. Maybe not.

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Perhaps a drain tile or pipe beneath it where it weeps down into? Magic invisible flashing perhaps? Careless installer? I don't know. Good point.

One of those pictures looks like there is a weep over the top of a window. That can't be right can it? That seems sloppy and like a built in window washing chore. Maybe not.

Weeps over window openings are correct. Look at any detail for brick veneer or rain screen construction.

I think you found the product that they used. (The MTI link in your post, above.) Thanks.

The installation spec for that system states, "Wall opening weeps should be installed at all low points in the stone pattern." I assume that means above windows.

Thanks again for finding that. It helps.

Jim Katen, Oregon

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Already mentioned and questioned: how does that install differ from a traditional brick veneer - other than using a more modern materials?

Forgive the absence of acccurate terminology right now, but how 'bout some sort of screen at the bottom of the exposed edges to keep the insects out.

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