What is the best way to prep the exterior of ICF block for synthetic stucco? Specifically, can I prefill the parting lines of the blocks with base coat, or should they be foamed and rasped down? I am concerned about telegraphing the lines through the finish coat. I plan to use STO NCP or total Wall S-2000 base, with mesh, followed by the appropriate top coat. Also, any recommendations on how long a rasp is necessary to get things flat? Thanks.

Hardrock,

There are a few really good rasps on the market that employ I think carbide chips that are permenantly attached to the rasp. (UGZ or Dura Rasp). Look either up on the web or call your local EIFS distributor and they should have them.

As far as prep goes, you need to follow the manufacturer's recommendations, some want you to tape potential seams and lines with their special tape and some don't. Ihave seen STO and looked a finished jobs but I have never used it.

ICF Contractor

Use a pressure washer. Don't get too close!!!Works great and takes the dust off at the same time. Most synthetic stuccos use EVA polymers in them. You can buy EVA in liquid form and add it to regular stucco mix. It sticks to the clean foam like you would't belive . I put it on the foam, put the mesh in the wet surface and spread another thin layer over that. Next day put on a top coat for about a total of 1/2 inch. When that is dry you can texture. Works great and you will have a thicker ,stronger exterior wall while saving a TON of money from not buying STO products. Most of the polmmer manufactures provide formulation information on using their products. No need to fill and rasp or any other time consuming prep this way.

Thank you both for the tips. Opus, your idea sounds pretty good. If I had more experience, I might try that.
I've already bought the Sto base and just picked up a foam gun to foam all the seams - I've had to chip concrete out of a few. ICFcontractor, I picked up a rasp (14") like you suggested - it sure seems aggressive.
Do you guys suggest primer between the base and top coats?
Hardrockcorp

"Do you guys suggest primer between the base and top coats?"

This is not an answerable question for a forum, because the manufacturer's instructions determine your answer!

If it is required by the mfg, and you don't use it, you have no warranty in the event of a problem.

Thank you, Jim. The Mfg. says it is optional.

You know "optional" kind of sounds like they recommend it, but want to avoid any association with the added cost.

I am spec'ing StoCorp as one of the exterior choices for an ICF house in CT

Jim, your probably correct - that makes sense.

excellent answer Opus!!!

I contracted to put Dryvit directly over ICF EPS foam. The installers rasped the entire wall surface flat (takes off any dirt, UV induced powder, etc.) At one point they used a rasp 2 - 3 feet long and an even longer straight edge to get a flat surface. Then, they filled any voids with base coat and let it dry. The base coat + mesh and top coat followed as per standard Dryvit. Got a very even. flat wall with no telegraphing of joints.

http://www.flickr.com/groups/855787@N22/ good exterior alternative, they use a pre-coat over fibreglass mesh. then this coating.
Just made a garden pond and planter out of ICF, easy, but it did creek a bit when the water went in.