I live in a coastal area on the water. We had an ICF retaining wall engineered to level the lot. 270 lineal feet of wall is exposed to sea saltwater spray and the back side will have fill dirt against it. The retaining wall is 6' high, and is built tight against a 20' sea wall which is 12' above the mean water level. The retaining wall is built on poured 12" x 16' engineered piers with a 3'x 1' poured beam on top of the piers. The contractor says they are going to fiber mesh the foam, and put on 3/8"-1/2" of stucco. Should the foam be waterproofed ? What should be applied on the surface of the foam on the sea side and the fill side? Thank you much.

Wow.....Trying to understand what you are saying....do you have your feet and inch symbols correct?

What is the purpose for using ICF for a retaining wall? Seems like a waste of $ for the foam and then protection over the foam on the exposed side. Why not find a contractor with concrete forms and use them to pour a solid concrete retaining wall? Or even concrete block and then just use a simple parge coat on the exposed surface?

Agreed. Not sure why ICF is pertinent to an non-living-space wall structure.
The only thing I can think of is that it's being used as a barrier layer to protect the concrete from chloride spray and build-up.

I know this response is very late to the basic, veteran, and advanced member responses to my question(s). None of the respondents answered my questions. Yes, the feet and inches are correct. The purpose of using ICF in this application is to drastically minimize the possibility of cracking by (1) keeping curing constant (2) keeping expansion/contraction of the concrete to a minimum (3) keeping as much salt spray away from any cracking that may occur to minimize rebar rusting and expanding, further opening the retaining wall to the elements over time. All CMU walls crack overtime and with this salt spray exposure will lead to deterioration and eventual failure much quicker than the ICF wall. I wish someone would have answered the questions that were very explicit rather than asking / reinventing the question. I did a lot more research and have a Great Wall that will serve it's purpose over a long time.

We would have recommended a solid concrete wall. For water work projects we always use high strength concrete with basalt rebar reinforcement to eliminate any possibility of reinforcement corrosion and concrete spalling. I don't think stucco over EPS will last very long in your application. EPS is also open cell and will allow water vapor penetration to the concrete core. Furthermore, hiding the concrete with EPS doesn't allow seeing potential failure indications before structural failure occurs. Presumably you had a licensed professional structural engineer design this retaining wall. This is not something to be designed just based on internet forums or construction contractor opinions. I suspect others would have provided more guidance too if you responded to their questions in a more timely manner.

Yes it was an engineered project by a registered licensed professional structural engineer. As the project went along, and unknown to me at the time, the engineer had spec'ed the EPS to have peel and stick membrane on both sides plus dimple mat on the interior side where a gravel drainage system was installed. Minimizing temperature related expansion/contraction and diverting water drainage were goals of the engineer. The Nudura EPS water absorption is 3% maximum. I still stand by my response about the the initial question and explanation being explicit, but the responses did not attempt to answer the question as stated, but rather asked if dimensions were correct and others asked why use ICF which was not part of the discussion. Thanks sailawayyrb, I appreciate that you took time to respond. Calm sailing.