The foam that the ICF blocks are made of is fairly vulnerable to damage from impact (e.g. getting hit by a board or rock) as well as from UV damage. Nearly all of it will be covered by the siding on the outside or drywall on the inside, but there is a small strip just above the grade that will be left exposed. This is by design, as even though we are using cement fiber siding it is not advisable to fill up onto the siding and thereby bury the bottom edge of the siding.
In order to protect this strip, we started applying a product called Dryvit. I’m not sure about the chemical makeup of Dryvit, but you mix together a half of a bucket of Dryvit with 1/3 of a bag of Type I/II Portland Cement. This creates a fairly workable mix that can be spread with a trowel.
To apply it, we spread strips of it vertically every 18 inches or so along the surface to be covered. Then a strip of fiberglass mesh 24″ high is stretched out along the wall just above the ground and embedded in the strips of wet Dryvit. Pressing the mesh into the surface with a trowel serves to hold it in place, and then you go back and cover the whole area with Dryvit, smoothing with a trowel as you go.
It sounds a bit easier than it is, and since it is a cement-based product, the length of time since it has been mixed and the temperature makes a big difference in how difficult it is to apply and smooth out.
One very important step is to remove the top layer of foam to make sure there is a clean surface to adhere to. This can be done with a long handled broom or something similar. The reason I know this is important is that I forgot to do it on the first wall that I did unsupervised by Doug, and he was able to easily peel it off a few days later as a result.
This is not terribly difficult to do, but is fairly difficult to do well so that the surface is smooth. I can’t remember too many house projects that I’ve done so far that have made my arms quite so tired. We still have quite a bit left to go, and it will need to be completed before the house is wrapped with Tyvek and the siding is put up.
