I will be building an ICF house next spring with an exterior stucco finish.

I have read conflicting reccomendations as to whether or not to add some material to provide a drainage plane between the ICF and stucco: 

Some say 'go ahead and just apply the stucco to the wall as it is waterproof.'  Others say to adhere to 'best water-proofing practices' because water intrusion at the stucco will travel to vulnerable areas like wood at windows and doors; but these folks don't specify how to best provide a drainage plane.

A related question: are some stucco materials better than others at preventing cracks/water intrusion?

Thanks for  this awesome fourm!

To begin, where are you located?

Keviin

First ask the mud manufacturer what best practice is for your area. Then ask your municipal building inspector what's required locally, as it varies, and he's the final authority.

Dear Embie...if you are planning on using a true stucco you will need an air gap. If you are planning on using an architecual coating it will adhere directly to the foam.

Your icf dealer should be able to walk you through questions like these and be happy to do so.

ICFgal

Thanks for the replies!

icfgal: is your answer due to the fact that an 'architectrual coating' can flex and therefore won't crack so it serves as an impermeable drainage plane?  I wonder if this would hold true in earthquake Bay Area California?

Just remember stucco is not a waterproofing. It is an aestethic covering for your ICF. NO horizontal planes without flashing are allowed. Flashing, then Elastomeric paint is the key to keeping water on the exterior of the stucco, as most stucco does not flex at all.

Rasp the foam very well and trowel in the scratch coat, even if you/your sub want want to spray the rest. Trowelling the initial coating into well rasped foam will ensure excellent bond long term. Beware the "one coat," "easy" process.

Kevin

embie,

I install 1/2" cement board over a drainage wrap to achieve a drainage plane and then finish the system with the Sto Quicksilver or other Direct Applied Finish Systems (DAFS). Expensive yes, but it will provide what you are looking for. It it necessary? From a designer's stand point, yes, the drainage plain is recommended. But I have had bare ICF walls go through a winter with no water penetration. It's you call.

If you are to install the system I describe, use an exposed web ICF and stainless steel cement board screws from McFreeleys. Install the cement board vertically and align the tapered edge centered on the webs. The wider the web you can find the better. I have learned that you want to cover the ICF as soon as possible with the cement board as the UV rays will break down the ties with the exposed webs.

Embie;

In the bay area all stucco on ICF I have seen is with building paper, mesh and scratch coat, than the top coat is with acrylic (architectural coating). The regular Architectural Coatings (or EIFS) are frowned upon since all the problems that occured MANY years ago that no one has forgotten, I've even heard the insurance companies won't cover you (That's a rumor, haven't looked in to it though)

Jelly:
Hoping to clarify;,
What happens with stucco is that moisture from humidity/rainfall is absorbed into the stucco. When the sun comes out, the moisture is actually driven INTO the wall, it does not evaporate off the outside surface.

Horizontal planes (window sills, thresholds, top surfaces of bands, quions etc.) must use flashing or several degrees of fall to shed the initial moisture through gravity. In addition, flashing behind the stucco in high exposure areas is paramount. Check out the stucco manuals, they are huge binders with details on how to flash properly.

Little story that helped us learn,
We used to have trim carpentry crews in Florida. Sometimes they would show up to trim a house, it would have an inch of water on the floor. Doors, windows, drywall, paint, roofing all having been installed properly. The CMU (concrete block) was usually not waterproofed yet, (usually a product called Link) nor stuccoed. When the rains were gone, and the sun came out in earnest, the interior walls would pour water into the interior....In a few cases the sub trades would run out of Link waterproofing (rolled onto the CMU then cementious stucco is trowelled on the CMU block) these areas would show moisture and efflorescence on the interior.

So it is important for the consumer to realize that although stucco is a great finish, its viability is largely determined by your ability to shed the water off the exterior, namely through flashing and elastomeric (stretchy) paint product AND an Exterior Maintenance program. Exterior Maintenance program is something all builders should show the consumer. Testing the viability of caulking, paint, mildew, settling flowerbeds etc. will allow problem solving before the problem is an insurance issue, which ends up hurting all of us.
Aside, Maybe a couple of new mandatory new high school classes are in order -home maintenance 101- along with -how to be responsible with money 101- so no child gets "left behind"

Being located in Wyoming, 10 inches of moisture a year and little humidity, no I would not put a drainage plane on my home. But in other localities of higher esposure, yes from my research it is recommended especially around windows and doors. Just my research, I don't know what all the codes now stipulate.

Keviin

I've done some more research on this: Portland Cement Association reccommends 2 layers of 'D' building paper under the lath and 3 coats to provide the air gap/drainiage plane; another source in the new JLC Moisture Conntol book reccommends 1 layer of 'D' paper and then a paper-backed lath to do the same. Both in combination with scrupulous door and window flashing.
I wonder if a final color coat with a DAFS product like Ted suggests would further improve the waterproofing and help prevent cracking to some degree?

embie,

Keep in mind the purpose of siding is not so much waterproofing as it is water shedding. Water shedding is just as much, if not more, effective than waterproofing and much more reliably achievable.

dmaceld...that makes sense to me...however, maybe I'm not 'getting' something as irnivek states above that:

'What happens with stucco is that moisture from humidity/rainfall is absorbed into the stucco. When the sun comes out, the moisture is actually driven INTO the wall, it does not evaporate off the outside surface.'

So I'm thinking that stucco (if water absorbs INTO the stucco) is not shedding but absorbing water and therefore that water can only be stopped if it meets a surface that will prevent the water from penetrating below where the water can then migrate below the door and window flashings.

My logic is that, given proper underlayment to help prevent water intrusion below the underlayment, a finish coat with a DAFS product (elastomeric coating) would provide an extra layer of protection. Or not?

I may be thinking into overkill as Sonoma County is hardly a raging storm center. But then I'm planning on installing some very beautiful and very expensive doors and windows on my home and I sure don't want them rotting from insidious creepy water crawlies from water migrating into the walls.

By saying migrating into the walls are you saying you want to prevent water from getting behind the siding material, whatever kind it is? If that is what you want, you are out of luck. And trying to make the outer surface absolutely waterproof will only exacerbate the situation. Let me try to explain why.

There is no way the space between the siding and the ICF surface, or sheathing in the case of frame construction, can be made absolutely air tight, as in a tightly capped bottle. So, it is a given that there will be some, however small, channels for air to get into that space. Now add the fact that the wall heats and cools during the daily cycle of day and night. That heating and cooling causes the air in the space to expand and contract. When it contracts air is drawn into the space from the atmosphere. That air contains water vapor. Then the air heats up and expands during the next daytime hours, and some air is expelled. However, when the air is expelled it does not carry away as much water vapor as was brought in when the air contracted. What you end up with is a pump that sucks water vapor into the space but does not push it back out. Eventually the vapor level reaches the dew point. This of course happens sooner at night than during the day. When the air reaches the dew point water vapor will condense out and becomes liquid water clinging to the backside of the siding and to the wall surface behind the siding. Now note this happens in the absence of rain fall. When you have rain fall the humidity in the atmosphere is of course higher so more vapor gets sucked in. We had to contend with this same problem in storing equipment outside where I used to work. Anything that had a closed space, such as a pipeline valve with covers over all the openings, would get moisture inside simply from the heating/cooling pumping action.

What has been described above about rain wetting the stucco and then evaporating into the space behind the stucco also happens to brick. In a building seminar last year the presenter commented that a brick veneer will pump more moisture into the space behind the brick than does any other siding material being used. Quite likely one reason this happens, especially with stucco, is that as the siding warms up after a rain the space behind it warms up faster. As the air behind the siding heats up it's capacity to hold water vapor increases. Water vapor migrates to the region of lower vapor pressure so the moisture in the stucco wants to migrate to the warm space behind it.

There are only two ways to move water vapor out of any space, move drier air through the space and carry away the vapor, or let it condense and drain down and away. One reason buildings from the 1800's have stayed standing in ghost towns is they were so air leaky that anytime the wood got wet there was enough dry air moving through to dry out the wood. We don't have that in today's construction, thankfully. The only sure way to keep a window or door frame and trim dry is to make it so that water, whether from leakage through the siding or from condensation, drains away from the frame and trim to the outside. In fact, lap siding such as Hardiplank must not be caulked along the bottom edge and really should be held slightly away from the plank below it. This helps create passages for air to move in and out from behind the siding thus increasing vapor removal by air exchange.

Go to www.jlconline.com and to the forums link. Go to the exterior finishing forum and do a search for 'window flashing' and 'door flashing.' You will bring up literally hundreds, if not thousands, of postings about flashing. It is a professionals forum so you will be not be welcome to post questions. Somewhere in those messages is a link to a window flashing tutorial site with good pictures showing how to flash and have dry windows and doors.

One thing I plan to do on the ICF house I'm getting ready to build is to take the metal flashing above the doors and windows and bend the top part back and kerf it into the styrofoam. That way whatever water flows down the styrofoam will have no path except to move onto the outer surface of the metal. This is part of the shingling technique that's been mentioned.

Hope this helps to clear things up a little better.

dmaceld,

Thanks for such a clear posting:  I actually understand the issue now.

Very respectfully,
Larry

There are some issues here about which I am confused...

I took a look at the forums at jlconline.com and noticed some discussions where it is mentioned a house with EIFS will not sell, and insurance companies will not insure it and homeowners are not allowed to install it. Geez. I know this stems from EIFS being installed on wood frame houses, not letting trapped moisture out because of the impermeable synthetic stucco, and thereby causing mold, mildew, and rot.

Concrete doesn't promote mold and mildew nor does it rot. But if you apply a synthetic stucco directly to an ICF form don't you essentially have an EIFS situation? Will you have problems getting insurance and re-selling the house?

Isn't a lot of this just about perception? If anyone from a bank, to an appraiser, real estate agent, insurance agent, or potential homebuyer, has the perception that EIFS in any form on any construction method is just plain BAD then I guess you're out of luck, even though it shouldn't cause any problems with concrete.

Or can you just call it something different? Does DAFS have the same bad reputation as EIFS? Is the only difference that DAFS uses a polymer added stucco while EIFS is a complete synthetic? If you use a polymer-added cementitious stucco directly applied to the foam would you still have the same problems selling your house?

As I've mentioned in other threads, I plan to build in Louisiana, but at the moment I live in central Europe. All you see here in new construction is stucco applied directly to exterior foam insulation. If it's new construction then it's cast concrete (or aerated autoclave concrete blocks, or thick partially hollow clay brick) clad in 3 to 4 inch thick EPS foam boards applied with screws and plastic washers and stucco applied directly to the foam. There is no felt, no lath, but you will see a fabric mesh. On some sites the stucco looks to be just portland cement and lime, unless they're adding a polymer themselves. On other sites I've seen them using Sto silicate products. But it's a quick process, and the end result is a really clean look and a beautiful finish. And they don't seem to have any moisture problems.

So if you have flashed correctly around window and door openings, shouldn't the foam should act like a drainage plane? And any water that does get into the wall will be absorbed by the concrete. Isn't the use of felt and lath with polymer-added stucco just overkill in ICF/concrete construction? Or are we only talking about using felt and lath with traditional three part stucco to make it stick to the foam?

Sorry for rambling...

Acrylic Stucco is very fast and easy to apply directly to most ICF's , and done  responsibly can be highly successful.
Care must be taken to ensure no trapped water within your ICF substrate. :-)
Most of our stuff has been direct applied, as we take responsibilty for ALL flashings, returns, backer rods and caulking.
Stucco is is SYSTEM with each element being equally important to the result.

Direct applied acrylic has NO drainage plane. Water must be directed outward in all places. Trims must be sloped.Metal Flashings ( Steel) used as necessary.

Only systems that incorporate "air gap" ,"stucco wrap" by Tyvek, breather material such as "cedar breather" as independant layers, or additional foamboard with vertical channels, can be considered to be Drainage Planes.
3 Coat Masonry Stucco with proper flashings and double felt,qualifies as air gap.
Continuous opening or venting along the bottom of all walls are a given.

Mac has given an excellent post above, and his window top flashing detail is perfect.Kerf the wall, and return it inward.
"Synerflash" sold thru Synergy has proven to be a useful peel and stick window flashing as it has a fuzzy outer bonding surface, which accepts acrylic really well.

For those that don't think water can travel in ICF's here is a pic for you.
The job was early on, after a good rain, and does not replicate a finished wall perfomance in any way, but the pic is useful to see.LOL

Most of the bad press about EIFS , and the problems related to it, were bad installs with poor flashing and no drainage planes.
Installer certification issues and lack of follow up by the suppliers led to an industry out of control.
The detailing is so important, yet, no site inspections by the manufacturers reps occured.

For someone worried about EIFS acceptance, documentation, by way of inspection reports from independant agency's and other industry experts, during the jobs progression, will go a long way to alleviateing concerns brought forward by your insurance company.

link