As a builder new to ICFs, I wanted to generate some discussion on secondary drainage planes, or the lack therof, in ICF exterior finishes, and any attendant issues that creates.  With stick construction, there should be a secondary drainage plane installed (building felt, Tyvek, Typar, etc) that handles any water that gets behind the primary drainage plane (the “siding”).  All the window/door flashing should be installed “shingle style” to keep any bulk water moving down the correct plane and back to the exterior.  EIFS/Dryvit, for instance has acknowledged the need for a secondary drainage plane, and their literature always shows one in an EIFS type installation.

 

There are numerous products available that indicate they can be installed directly over the ICF, e.g. Sto, Total Wall, Dryvit, Grailcoat, etc.  This is of course an attractive proposition due to simplicity/cost/time reductions.  The products mostly seem to advocate keeping the water out through chemistry (most are ‘waterproof’).  None of the literature on the web sites indicates how water intrusion is handled when it actually occurs, which of course it will.  In speaking with a Dryvit distributor, their explanation was basically that EPS and concrete can handle being wet and so it is OK.  Not exactly the building science explanation I was looking for, nor one I feel comfortable with.

 

Is a high perm level sufficient to allow moisture to dry to the exterior?  Sto, for instance, has a vaper permeance of 34.  (I haven’t talked with Sto yet to see if this would be their explanation) Dryvit Residential lists a perm of 7 and so would dry much more slowly.

 

The block I am looking at (AMVIC) has vertical channels every inch or so.  Can/do these channels function as a drainage path even after receiving a base coat?

 

Has anyone done the traditional 2 paper coat/metal lath in conjunction with one of these 2 coat systems?

 

JD Hanson

 

JD,

When talking about Architectual Coatings such as Dryvit, Sto, and so forth you have to understand these are not EIFS (Exterior Insulation and Finish System). These are coatings used in the EIFS process.

Here in the Pacific NW we had a huge issue with EIFS installers not properly installing their EIFS components and had many failures. In stick construction you will get moisture behind the foam with an EFIS system due to dew point and interior moisture as well as possible intrusion. In ICF construction there is not the space or potential space for the moisture to form because the Architectual coating bonds directly to the foam that is directly bonded mechanically to the foam in two ways with no void space for moisture to form. The problem with the EIFS system in the PacNW was not the coating separating from the foam but the foam separating from the wood building. This happened for many reasons such as connector corrosion due the wrong cheap connectors that would not stand up to misture. Installing in the rain. No weep holes. and the list goes on.

With ICF these issues don't occur. Concrete, properly consolidated, that has reaches 5000 PSI is considered impervious to water. So truely any exterior finish you put on an ICF building is only there for looks and needs to be installed to protect itself. Of course you need to pay attention to your openings and insure proper flashing and installation.

ICF Contractor

I have some of the same concerns as the OP.  I did not present them as well or as thoroughly.  Two questions:

Are you advocating a system where the plaster is bonded to the foam over a paper and wire system?  Is the paper and wire system inferior when used with ICF's?  Or is it just a matter of preference for the installer?

I still do not understand the flashing of openings, windows, etc.  It seems that no matter how well done at some point in the life of the building moisture will intrude.  What happens to it without an escape route? 


Thanks,  John

JC- We are in FL and have supplied a number of projects with materials for exterior ICF finishing. It seems to be a builders choice. Paper lath and stucco is one method. We see stucco finishes applied to the foam, directly, all the time. Clean, rasp, apply link(bonder), add fiber to the base coats, set and finish. Waterproofing of openings is critical. One method is a 2 part system using products like SealoFlex or Hydrostop. Applying an embedded fabric with these water based products has had great results. It will always be how good the materials installation and details that will prevent problems down the road.

I have spent some time on the Sto web site today looking at their ICF coatings. I am impressed with the level of information and the fact they actually address this issue of water management. They point out that there is no secondary drainage plane, so if you are applying their EIFS coatings directly to the ICF you had better detail your openings really, really well. They even go so far as to say that if you are uncomfortable without a secondary drainage plane, you should consider an EIFS or Stucco application to get that secondary drainage plane.

John,

What I advocate is the use of an architectual coating such as STO, Dryvit, ECO, and the like applied to the manufacturer recommendations typically right to the foam. I feel these systems have proven themselves to be superior. With a typical metal lathe type application I believe you are adding components to the system that increase your chance of failure.

As for the windows we take the most conservative approach. The issue is that depending on the widow you are installing you will get a different recommendation to how they should be detailed.

ICF Contractor