 Exposed insulating concrete does gather water
And should never be used as the permanent outermost coat of your oven. I have a dome that I stuccoed, with a stucco heavy in latex to repel water. Any water-repelling solution will work.
Now the water won't harm your oven directly, but if you build a big fire after a heavy rain the water the vermiculite/perlite/pumus will expand and possibly crack! Yikes, that would be terrible. Well, you'd have to patch it.
So what the other posters said is right on the money...cover with a tarp until a permanent solution becomes available. Stucco and gabled house are the two most common, but indoor ovens need none of that, they're protected from water by a "house".
Happy baking
Scott |