[CanuckJim]

Mfiore,

I really don't have a lot to add to what's already been said, except to sum up. There's a great deal of difference between mortar that's set and mortar that's cured. The whole point of keeping mortar wet for the first few days is to slow down the setting and permit the curing. Really, it's advisable to keep slabs wet, under burlap or tarps, for the first three days or so. This prevents rapid setting, shrinkage, cracks and affects strength. Brick joints don't really need that kind of attention, unless the weather is very hot and dry and the structure is in direct sunlight. Using a spray bottle would work. Heat, dryness and sunlight will allow far too rapid drying of the mortar, leading to shrinkage. If the outside of the dome is to have cladding on it, that should be treated the same as a slab. Tenting keeps the work out of direct sunlight, as well as protecting the mason. Allowing fresh mortar or concrete to freeze is a definite no-no.

The whole point of all this is to create the best conditions for curing. Mortar and concrete cure in 28 days; it's an exothermic reaction, not an air cure, and can't be rushed.

All concrete and mortar creates heat as it sets (exothermic); refractory mortars and concrete create much more than conventional ones. Kept wet, the heat--and therefore shrinkage--will be reduced. I once poured a six inch thick hearth slab out of LaFarge Fondue. The surface didn't get hot enough to fry an egg, but it was close. Kept that one wet for four days out of direct sunlight.

It sounds odd, but at first keeping things moist is necessary, while later you want to slowly drive the moisture out of the oven. No, rain won't affect even well set joints, but firebricks will absorb a ton of water, which you will have to drive out later. Best to avoid that. Getting insulators wet is never a good idea.

Jim