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How do you finish the exterior of slab on grade?
Dave Derouin
Oct. 18, 2018Updated: Aug. 2, 2020
I am looking at your example of a slab on grade construction technique and wondering how you finish the exterior of the footing insulation once the forms are removed, specifically the top of the roxul that would be exposed after building the exterior walls.
Just to be clear when you say the 'top of the Roxul', the top horizontal edge of the slab insulation has more insulation sitting on top, so there is no exposed 'top' as it were. But I'm thinking by 'top' you may mean the top vertical portion that would be exposed to the weather, so I'll answer that one, let me know if I misunderstood :) You can see exactly how we did it here in this video -
How to finish the exterior of a slab on grade foundation insulated with Rockwool
What we did worked, though in hindsight given the compressibility of the Roxul (certainly at 8 inches thick) we would have included more fasteners as we found it to be a little spongy for our liking. This still can be remedied by using a flexible parging product, which is sprayed on and leaves a little room for movement without cracking.
As a point of interest, earlier this week we just broke ground on our next demonstration house that will have an air-heated radiant floor where most of the heat is provided by solar air heating panels. It is much easier to finish the exterior of an EPS foam foundation kit, all you need to do is parge it. See below the slab under construction.