perlcrete insulation in winter

[chickade]

I have my blankets over the oven and want to do my perlcrete layer. I have burned several fires, but don't want to cook with the blanket exposed. However it is getting cold, especially at night. I would rather not put off completing the project until spring. Can I keep the oven warm over a period of a few days to help the percrete set? Do I have to worry about the water in the perlcrete freezing overnight?

[Gulf]

Re: perlcrete insulation in winter

I have my blankets over the oven and want to do my perlcrete layer. I have burned several fires, but don't want to cook with the blanket exposed. However it is getting cold, especially at night. I would rather not put off completing the project until spring. Can I keep the oven warm over a period of a few days to help the percrete set? Do I have to worry about the water in the perlcrete freezing overnight?

You will have to keep any masonry project from freezing in the early stages of the curing process. I am not from an area that has to deal with the extremely low temps that you yankees have to endure. However, I do think that covering your project with a waterproof tarp or thick plastic, and a heat lamp inside your dome will do the trick. I would use some type of spacer between the between the outside of the pcrete and the covering though. If you could enclose the whole oven in pop up tent as some have done that would be great. But, don't fire the oven to keep it warm, as that might dry it out before it is cured. And, my advise to your direct question: Don't let the pcrete freeze after application for 2 or 3 weeks. 28 days is optimum.

[Tscarborough]

Re: perlcrete insulation in winter

Actually, the rule is 40 degrees and rising at placement, 24 hours above freezing after placement. Perlcrete is a special case, but 48 hours without freezing (via blankets, tenting, or ambient), should be fine.

Once the cementious reaction (initial set) takes place and there is no more free water, freezing temps do not affect cementious materials. Free water is what crystallizes and expands.

[david s]

Re: perlcrete insulation in winter

Given that vermicrete takes about double the amount of water that normal concrete takes, then there is a lot of free water. ie. about twice as much water as is used up from hydration. Not sure what will happen if this freezes as we never get anywhere near freezing point.both vermiculite and perlite are somewhat elastic so maybe it'll work out ok./

[Gulf]

Re: perlcrete insulation in winter

I just looked at the 10 day forecast for Swarthmore, PA. It does't look all that bad (30's and 40's). I tend to think of every place "northern" as temps in the low teens . I also don't know very much about perlite. I can only assume that it is simular to vermiculite. I also don't know how "free" it is, but there is a lot of water "trapped" in each of those little sponge like vermiculite cells .

I think you will be ok with TScar's advice. But, for someone building in an area which the temps will fall into the 20's, I would protect it from freeze a little longer.