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Cold weather masonry - Forno Bravo Forum: The Wood-Fired Oven Community



I'm Peter Reinhart! Ask Me Anything! Monday, February 15, 2016 7:00-8:00 pm EST

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Cold weather masonry

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  • Cold weather masonry

    I'm reading that masonry doesn't hydrate under 40 degrees f. Does that mean that I'm through for the season? It was down to 31 degrees last night, although it's warmer than that during the day.

    Any words of experience from masons would be appreciated.
    My geodesic oven project: part 1, part 2

  • #2
    Keep it covered

    I poured my foundation last weekend. It got down to 19 deg F. I put tarps over it and a bunch of blankets. I also slipped a thermometer under the tarp - the next morning, at daybreak, it was reading 44 deg. Your situation is a bit different, mine was a simple flat pour.

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    • #3
      cold weather masonry link


      From this it sounds like we can still work for a while....

      My oven progress -


      • #4
        Cold Weather Masonry


        I'd be careful with low temperatures. Hydration is one thing, but set and cure are two others. No matter what, you'll need 28 days for a full cure. There are accelerants out there that will speed the set, but strength will be affected. If the mortar freezes before setting, it will effloresce and be weakened, sometimes leading to cracking--and spalling over time.

        If you must continue, add a small amount of accelerant to your mortar, keep your materials dry and warm, use warm water (72 F), invest in an insulated tarp (usually white) and use some sort of heat source under it (lights, for example) to keep the temp above 40F--50 would be better.

        I know it's tempting to keep going, but the risks probably are not worth it. As a mason, I can tell you that I would never buy a house bricked in winter, no matter how well the site was protected.

        In my estimation, the risk factor outweighs the benefits. You need strength in your mortar because of the stresses it will undergo from heat. Mixing mortar in less than ideal conditions would put enough doubt in my mind so I simply wouldn't do it. Mortaring up brick veneer on a building is not the same as building a brick oven.

        "Made are tools, and born are hands"--William Blake, 1757-1827


        • #5
          From that link it seems like mean daily temperature that counts, and I should be OK this month, longer if I take the building materials inside (easier to work with, too)

          Here's the link for mean monthly temperatures for various US cities.

          My geodesic oven project: part 1, part 2


          • #6
            Good to go with Caution?

            You are not insinuating that it takes 28 days above freezing for a masonry project to cure are you? If that were the case, New York City would still be dirt and trees. I poured my driveway in February many years ago and it hasn’t cracked a bit (and it was friggen cold). All I had to do is keep it covered for a few days. Concrete generates its own heat – you just need to retain it for a cure. There are many masonry projects that can be done in a somewhat cold environment. Obviously the temps need to be above freezing before you begin.
            With that said – you do live in Canada and I’m sure you see more extremes than the lower 48 would ever see (or Nevada ).

            Just my 2 cents,

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            • #7


              Nope, wasn't insinuating any such thing. Curing is mainly chemical, once the cement has set and the green stage hydration has been driven off by the heat generated.

              I once met a man in Palm Springs who had that "Canadians ski in July" attitude. He was from North Dakota. When I told him I lived to the south of his location, he refused to believe me. Produced a map and won a fifty buck bet on that one. Even so, here we do get wide temperature swings, occasionally as much as 40 F in one day.

              Really, I don't want to get into a technical analysis of how cold weather affects mortar. I've used an awful lot of it, cold weather and warm. Under the pressures of commercial work, it does happen that things are built in freezing conditions. What I was trying to say is that freezing weather linked to mortar is chancy at best, and for an oven you want the strongest possible mortar.

              That's all.

              "Made are tools, and born are hands"--William Blake, 1757-1827


              • #8
                Re: Cold weather masonry

                I have a couple of questions for you guys. I'm close to finishing. Technically, I think I'm done. I have a scratch coat of sand topping concrete over wire lath. I have most of a second coat on but had to stop because of rain. I think that if push came to shove, this would be enough to protect the dome and insulation from weather. I also plan to cover it with some sort of sealant. I'm hoping to finish the second coat of of concrete tomorrow and, weather permitting, I plan on putting a tinted coat (Terra cotta) of straight portland or a portland type s mortar mix. (I have half a bag of mortar left over) I think that I will be able to get a more uniform surface with the straight Portland, and it will be easier to work with. I plan on using either a tile grouting float or a green sponge float to finnish it.

                So, What do you suggest I use for a sealant, either on the scratch or finnish coat? And, does anyone have an opinion on the suitability of straight portland cement, tinted or otherwise? Will it crack, hold up? I live in the northeast outside of Boston and we are about to go into winter. I really want to get it fininnished before it gets too cold.

                Any help and advise will be greatly appreciated.



                • #9
                  Re: Cold weather masonry

                  Since we are discussing temperatures etc. I don't think I am going to get mine finished before the end of the "season" and it seems that the clay/sand mix I used to level with (it may be a tad too thick in places but I am level) is still moist. I do have a tent over it so no direct moisture but our weather has been wet. Would an open fire on the floor be necessary to dry it out or is wet clay less of an issue. I do imagine that the water in it would be prone to freezing. Thoughts/suggestions/advise

                  Thanking you in advance

                  Member WFO-AMB=WW


                  • #10
                    Re: Cold weather masonry

                    Above 40 degrees portland concrete will cure at nearly the same rate as higher temperatures.

                    Between 40 and 32, the curing will slow down considerably. As the temperature rises it will re-start with no harm done.

                    Freezing temperature is a killer for curing concrete. The curing will stop and ice lenses will rapidly form. The concrete will never cure to anywhere near maximum strength and you are likely to get spalling. Note that curing concrete generates it own warmth - sometimes a simply covering of the concrete with wet towels or a tarp is sufficient.