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Old 05-29-2014, 06:28 PM   #1
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Idiot-check this plan


My exterior walls have a layer of stucco that's in okay condition, but was stupidly covered in a bad layer of spray stucco that's peeling off everywhere. I can't have a new layer put over the top because it won't adhere properly. So I'm thinking that instead, what I should have done is take the opportunity to put insulation boards over the stucco and have a new layer of stucco applied over that.

So this would be the wall sandwich, interior to exterior:

Drywall
Studs + fiberglass batts
Plywood
Two layers of building paper
Traditional hardcoat stucco
New insulation boards; two layers of of 2" thick EPS boards with staggered and taped seams
New stucco + lath


Couple of questions about the sanity of this plan:

1. Can I realistically use two layers of EPS foam to avoid having to add a new water control layer? There's already such a layer in the wall sandwich (the building paper under the existing layer of stucco), and the boards will be staggered.

2. Since traditional hardcoat stucco is heavy and would be applies to a wall surface that's cantilevered out 4", would it be sane to use surface-bonding cement or some other cementitious one-coat product?

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Old 05-29-2014, 06:32 PM   #2
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Idiot-check this plan


How about an EFIS cover-up?

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Old 05-29-2014, 06:34 PM   #3
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Originally Posted by Bud Cline View Post
How about an EFIS cover-up?
That's basically what this would be. Only with the insulation being 4 inches thick and the stucco being more of a traditional cementitious variety rather than face-sealed and polymer-based.
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Old 05-29-2014, 07:27 PM   #4
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Without some footing to support the weight, the stucco is going to strip off what every you hang.

If you watch how they hang the mesh for stucco, they nail right into studs.

Assuming normal 3 layer stucco....7/8" thick....each foot of wall 8' tall is going to weigh over 80 lbs. So, a wall 10' long is going to be over 800 lbs.

I think your going to have a hard time keeping something like that from shearing off your existing wall.
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Old 05-29-2014, 07:59 PM   #5
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Originally Posted by iLikeDirt View Post
That's basically what this would be. Only with the insulation being 4 inches thick and the stucco being more of a traditional cementitious variety rather than face-sealed and polymer-based.
No it's not!!! Not even close.
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Old 05-29-2014, 08:52 PM   #6
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Originally Posted by Bud Cline View Post
No it's not!!! Not even close.
I know it's not the same, but isn't EIFS:

1. insulation board
2. drainage plane
3. synthetic stucco
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Old 05-29-2014, 09:21 PM   #7
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Originally Posted by iLikeDirt View Post
I know it's not the same, but isn't EIFS:

1. insulation board
2. drainage plane
3. synthetic stucco

EIFS is typically Styrofoam, adding no significant weight to the process. It can be attached with adhesive having no significant weight to it. Then a thin base-coat of a cement product adding no significant weight to it, Maybe some Fiberglas reinforcement adding no significant weight, and a synthetic top-coat possessing no significant weight. See where I'm going with this?
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Old 05-29-2014, 09:43 PM   #8
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Originally Posted by Bud Cline View Post
EIFS is typically Styrofoam, adding no significant weight to the process. It can be attached with adhesive having no significant weight to it. Then a thin base-coat of a cement product adding no significant weight to it, Maybe some Fiberglas reinforcement adding no significant weight, and a synthetic top-coat possessing no significant weight. See where I'm going with this?
I don't, really. The EPS insulation board I'm talking about is Styrofoam. Same thing. And it certainly doesn't have no weight. It's between 1 and 2 PSF. And how can a thin base coat of any cement-based product add "no significant weight?" The surface-bonding cement I'm pondering using as a stucco substitute weighs maybe 1-3 PSF (vs 10 for traditional hardcoat stucco). Source: http://www.homedepot.com/catalog/pdf...4b7609398a.pdf

Finally, this BuildingScience document about the very thing I'm proposing describes a test of four inches of EPS foam screwed to the wall sheathing, finished with traditional 10 PSF hardcoat stucco, and found a final vertical deflection of less than 1/32" after 6 months.

So given that BSC basically already tested what I'm proposing to do and found that it worked, I was hoping to see if anyone had any kinds of personal experiences with this type of installation or if any part of it didn't make sense given the science behind it; maybe if I misinterpreted something?
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Old 05-30-2014, 10:48 AM   #9
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Additionally, http://www.buildingscience.com/docum...s-younger-then

Really cool article about Joseph Lstiburek doing something pretty similar.

Quote:
I built a test wall and tested it until it broke. Six fasteners for every 4 ft x 8 ft sheet of insulation. Two at the top, two in the middle and two at the bottom. Eight inch thick foam. No way that would work. Except when you built it, it did. You could hang a pickup truck off that wall.

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