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We break ground in May, to build our new home, using a set of plans originally done by architect (and FH monthly contributor) Sarah Susanka. A feature of the exterior is the stucco wall finish, which is used as a “base” element of some walls. It is detailed with furring underneath so that the stucco portion of the wall, from finished grade up to a wood-trimmed transition ledge, appears thicker than the wall above, which is finished in cedar clapboard. The plans distinctly call out stucco, not EIFS, and section details confirm it to be of the approximately 1″ thick portland cement variety. My question is this. Who has seen a stucco finish “stood off” from the structural wall underneath, on furring? I am thinking we will spike 2x furring through the sheathing into the studs, and over that furring we will do the felt paper, then the stucco wire lathing, followed by the scratch, brown, and finish coats. The drawings show (and photos in Ms. Susanka’s books of her home, also show) that the stucco goes down to finish grade. EIFS specs are firm about terminating their cladding 8″ above any finish grade. Should we be certain to use treated lumber as our furring (it will be over the concrete foundation walls at this point), or might we instead be advised to not use lumber at all to fur over the concrete foundation wall near and below grade, and instead use 1-1/2″ rigid foam? BTW, Ms. Susanka is too busy to deal with this for me to ask. She is not the architect for my project; the plans were bought from a plans service to whom she sold the distribution rights.
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Gene,
If you stretch metal lath over felt across 2x furring and then apply stucco you will encounter several problems. One being the fact that the felt will gap under trowel pressure. Second, without a rigid substrate you would have just built a largely unsupported, very heavy stucco wall that will likely be more petulant than an oversexed 15 yr. old daughter. The pressure applied when troweling on subsequent coats over an unsupported base layer will likely cause crazing throughout, or alternatively, if you stand there and make sure no one pushes too hard, a totally ephemeral bond.
So, either build out with foam (good idea) or apply a second layer of sheathing, or? If you post graphics of the precise areas of the home to be stuccoed, showing relationships, we could be more help.
In a nutshell, building paper is not a substrate.
Lance
*How about 1x furring and 3/4" ply sheathing 2 layers felt expanded lath stucco . My grand father said to use 2 layers of felt ,it stored and transported more water to the bottom and out from the house. It also gave the added protection if you cut the top layer.
*Here is a graphic. The height of the stucco section that is over the framing above the mudsill, is about 33 inches. I watched a contractor do this "fur out stucco over wood frame" on a wainscot on a very high end house being built by Dean and Robin on the television show "Hometime." The house is named "Maple Forest House" and was featured in a story and on the cover of a past issue of FH.You can see how the built-out stucco wainscot goes to grade.
*Gene-I think what this graphic is showing, albeit somewhat unclearly, is 2" furring fastened to the frame but with 2" foam infill between the nailers creating a full substrate. If this is the case, then 2 layers of felt under expanded metal lath sounds good. I'd use stucco nails to space the lath out from the paper, thereby embedding the lath into the center of the stucco rather than merely backing it.Also, metal lath has a "grain," you want the sharp edges to oppose gravity, providing more tooth to the stucco, so they should be applied facing up.Also, the washed river rock will minimize the stucco standing in water, if the finish grading of the layers beneath is done well. But, in time it will fill with organics and lose its effectiveness as a drainage plane. Careful consideration needs to be given to the termination of the bottom edge of the stucco assembly at the control joint and below grade to allow for escape of water that may have entered above while at the same time providing a termite barrier if that stringently applies in your area.For the areas below the control joint I'd consider using 2" larger (interior to exterior) block. Then all you'd have to do is parge it and you're good to go. Then the effective termination of your assembly is the control joint, with no foam below grade to allow concealed entry for insects.Lance
*Gene,I couldn't agree with Lance more. Don't try to free float Portland Cement (PC) stucco. It will crack. I'm working cracking issues on 52 housing units down at an airbase in Florida. The houses have massive hairline cracking. The problem? PC stucco over a relatively flexable substrate. (Cheap OSB) If you can create a stable substrate with foam insulation and furing strips then use properly installed expanded metal lath, you should be OK.
*Definitely go with two layers of felt. That's an important detail because the stucco contacting the first layer of felt may enable water to pass through capillary action. That slight seperation between the two layers can then serve as the drainage plane. At least so has said Joe Lstiburek.Andy
*Gene, they have a lot of experience in the Vancouver BC area with installing stucco on furring with an airspace between the stucco and the substrate. They call it rainscreen stucco (concept is the same as the rainscreen wall presented this month in FHB). Cracking was an issue when this detail was first used, because the plaster thickness was greater between the furring. (differential thickness = cracking). When installing stucco on furring, they are now using a heavy asphaltic board called "breather board" as the underlayement behind the stucco. It is about 1/16" thick and feels like museum board. This is installed over the furring first, then the lath, then the stucco on three coats. All the other typical details are the same (control joints, stops, weep screed, etc..) There is a company in the Vancouver area that makes the breather board (Hal Industries). Don't know if anyone in the states makes something similar.
*Rolling in all the combined wisdom, my details are now proposed to look like the attached. Note that rigid foam now fills the void between furrings at the area above the mudsill. PT furring is used below. My gravel fill comes up to just below the bottom weep edge of the stucco below the mudsill, facing the foundation wall. Comments, please?
*Gene-The text on the graphic is difficult to make out but it looks like you're indicating the felt or stucco wrap be placed over the foam & furring. In any event, you might want to consider stapling up 2 layers of felt beneath 2" foam without furring, attaching the foam with a couple of tack screws and then the lath to the frame and sheathing (through the foam) with long screws and fender washers. Stucco likes to stick to foam...Truly, the only places (above the joint) that you might need furring are at the top and bottom edges to facilitate attaching cap, flashing, etc. and the joint screed at the bottom.I've applied PC stucco exactly like this and it proved convenient and resulted in a uniform, very sound substrate, as we placed 1 screw every six inches with enhanced grip on the lath provided by the fender washers. It worked especially well at outside corners where we could control tension on the lath by angling or easily re-setting the screws.Lance
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We break ground in May, to build our new home, using a set of plans originally done by architect (and FH monthly contributor) Sarah Susanka. A feature of the exterior is the stucco wall finish, which is used as a "base" element of some walls. It is detailed with furring underneath so that the stucco portion of the wall, from finished grade up to a wood-trimmed transition ledge, appears thicker than the wall above, which is finished in cedar clapboard. The plans distinctly call out stucco, not EIFS, and section details confirm it to be of the approximately 1" thick portland cement variety. My question is this. Who has seen a stucco finish "stood off" from the structural wall underneath, on furring? I am thinking we will spike 2x furring through the sheathing into the studs, and over that furring we will do the felt paper, then the stucco wire lathing, followed by the scratch, brown, and finish coats. The drawings show (and photos in Ms. Susanka's books of her home, also show) that the stucco goes down to finish grade. EIFS specs are firm about terminating their cladding 8" above any finish grade. Should we be certain to use treated lumber as our furring (it will be over the concrete foundation walls at this point), or might we instead be advised to not use lumber at all to fur over the concrete foundation wall near and below grade, and instead use 1-1/2" rigid foam? BTW, Ms. Susanka is too busy to deal with this for me to ask. She is not the architect for my project; the plans were bought from a plans service to whom she sold the distribution rights.