What is the best way to do exterior foundation styrofoam finishing?
I have never done exterior foundation insulating because I have never seen a good looking and long lasting finish. Even parging on concrete only lasts so long depending on the methods and materials in application. I have always tried to use new form ply where it had to look really good.
It is also the reason I have to done any styrofoam block foundations. I saw a reputable company do some parging over a mesh on the styrofoam and two years later it was all flaking off from the frost.
The only one I have ever seen look ok was a Pressure treated ply over the styrofoam. Problem was the frost pushed the plywood upwards and the owner had to keep cutting off the top edge every few years.
Anyone have any ideas?
thanks in advance, george
We have never had a problem with parging staying adhered. I wonder if maybe what you’ve seen wasn’t a great product maybe? Or perhaps it wasn’t mixed well or installed well. For EPS foam, you can scratch up the surface and parge directly to it, or you can install a cement board over top, though you can come to the issue of how to attach the cement board. We installed cement board over rigid rockwool insulation on the exterior of a slab we did and had to rig up a method to attach them. It’s pretty redementary and we would do it differently in the future but it did work. you can see here in this video –
How to finish the exterior of a slab on grade foundation
If you say you saw a foundation with parging flaking off in two years, that sounds like it wasn’t done well and I would hope that would fall under a warranty if it really was a reputable company. My basement foundation has exterior rigid EPS foam panels, and to finish it I attached a diamond lath to the foam with roofing nails to hold the parging, and did three coats. Its close to 20 years now and it looks perfect. The only risk is that it is softer than concrete obviously, so if you smash into it or even kick it pretty hard you could likely break the parging, but that’s never happened to me.