Weather proof

[mfiore]

Again, another question to reveal my inexperience with masonry.

A recurrent theme in the forum is the need to keep the masonry wet while curing. Freshly poured cement is kept wet and covered with plastic to keep from drying while curing, bricks are soaked prior to using to prevent mortar from drying out, the freshly mortared domes are hosed down to keep from drying too soon, etc.

Yet I see several builders putting "tents" or tarps over the work sites, presumably to keep out the rain. Is there a problem with the unfinished ovens from getting rained on? It seems as that would be a benefit. Is there something that is not water-proof that I am missing? Seems to be just brick, mortar, and cement. What is the benefit of the tents? I'm sure they are not their just so you crazy WFO builders can continue to work in the rain.

[gjbingham]

Re: Weather proof

From my readings on this forum, the mortar, depending on the type, is not waterproof and will absorb the rain and get soft/mushy again. Misting concrete and stucco while it cures is recommended. Total saturation is not recommended.

[mfiore]

Re: Weather proof

Do you know what type of mortar that holds true for? Is this only until the mortar dries, or are certain types of mortar always at risk for water injury? I assume once the mortar dries, you should be safe if it gets rained on.

[gjbingham]

Re: Weather proof

Nope, I'm not that educated. dmun and Canuk Jim can give you lessons in mortar that will make your head hurt. Someone will chime in that knows the physkcal qualities and weaknesses of refractory mortar.

I wouldn't, for the time being expose Heat Stop 50 or the homemade lime/portland cement/water/fire clay mix to prolonged rain. Refmix - no idea.

[Xabia Jim]

Re: Weather proof

Rain is only an issue for the first day or so with normal mortar and concrete projects. Once it has "set" rain won't usually wash it out.

On a block wall, pad or stucco project, I'll mist it the first day and switch to a hose the second day......that's just me, lots of people are less anal about their cements....

[Frances]

Re: Weather proof

I think a lot of people DO have tents so they can continue working in the rain (and snow and hail...). Acoma, got anything to say about this...?

That and a lot of us have been working towards winter, and got worried about the uncured mortar freezing. The inside of a tent can be kept just above freezing even if its below outside.

What kind of mortar are you planning to use?

[Inishta]

Re: Weather proof

I have no idea what the constituents in the brick mortar for my oven were but I was advised not to get the dome soaked unnecesarily. Seems there may be a problem.

As Frances says, I think the tents were more for the protection of builders rather than ovens.

[dusty]

Re: Weather proof

Yea, the tent plus heater made it very comfortable in the cold, but I didn't want the vemiculite-concrete to get wet either. It soaks up water like a sponge and takes a long time to dry out.
Now that I am done, I have the woven ceramic blanket insulation on top and that can't get wet.

dusty

[CanuckJim]

Re: Weather proof

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

[mfiore]

Re: Weather proof

Great information from all. I appreciate it. I will likely use the RefMix mortar. It looks like I, too, will be putting up a tent!

Thanks again