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Foundation finishing over exterior Comfortboard insulation

cmylks | Posted in General Questions on

Hello all, we are working on a plan to cover the 1-3feet of exposed exterior insulation on the foundation between the soil level and the start of our siding (I say 1-3 feet as it’s 1 foot on the north wall, and the west wall has a slope so the exposed portion is up to 3 feet on the lower end of the grade). We are considering to use the ‘belt and suspenders’ approach described by GBA member Riversong (see post from 2010: 

He describes using surface-bonding cement over metal lathe / 1/2″ hardware cloth to cover the exposed, above grade portion of exterior insulation.  In our case, the insulation product we’ve used is the semi-rigid Rockwool Comfortboard 80 not rigid foam. Our local contractors supply guys have cautioned about the cementitious coating over Rockwool due to moisture issues – they fear that there could be efflorescence over time on the cement coating.

I wonder if anyone has applied a cementitious coating over Comfortboard before, or has any other suggestions. We wondered about installing a vapour/air barrier between the Comfortboard and the metal lath for exampe to stop/slow moisture transfer to the cement coating for example?

(Note: we are in Eastern Ontario, climate zone 6)

Thanks so much for any comments, tips or suggestions. 

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  1. shedworkshop | | #1

    Did you end up using this? I'm leaning toward using surface bonding cement over 1/2" galvanized steel hardware cloth to protect Rockwool Comfortboard. I've also seen products labeled as "foundation coating cement" and am wondering if that would be better.

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