Brick layer advice

[GH85Carrera]

We have some minor brickwork needed on our mailbox. I have "a guy" coming over to do it on Wednesday. My question is not about the brickwork, but the temperatures. Mortar is mixed with water. Will it "dry" or set in just hours?

Wednesday is going to be 48 degrees and partly cloudy. But Wednesday night, the dang Russian Siberian air gets here and some forecasts show a low of 2 degrees. It seems crazy to have anything mixed with water with crazy cold temps on the way and it does not get above freezing until Sunday afternoon for a while. The below freezing overnight.

[masraum]

Cement is exothermic when drying, so I assume the cold may not impact it too much. It may not be ideal, but my guess is that it's probably not a show stopper.

I remember some show, maybe mythbusters or something like that talking about the old "cement shoes" and how your feet would be burned in the process. I don't know that it gets THAT hot.

[masraum]

https://www.madgetech.com/posts/blogs/maintaining-the-ideal-temperature-during-concrete-curing/

First things first, if it’s hot enough where you don’t want to leave the comfort of your air conditioning or cold enough that you need to put on a hat and gloves, you shouldn’t lay concrete!

It’s advised that concrete be cured at a moderate temperature between 50 °F – 90 °F. In a perfect world, the temperature of fresh concrete should be above 50 °F, but cured and maintained at 50 °F. But if you can’t hit the 50-degree mark spot on, concrete cured within these temperatures will outperform +90 °F concrete in strength and durability.

But, that may be for ideal strength on something like a home foundation or driveway. It may not be as big a deal for bricks.

[stevej37]

I've seen some of the neighborhood mailboxes that after the brick work is done...it is wrapped with black plastic and left on for a day or so....when the temps are low.

[masraum]

More interesting info with lots more details. I think one of the items says "keep it above freezing for 24 hours".
https://www.thespruce.com/expert-tips-on-how-to-cure-concrete-in-cold-weather-845024

Maybe you could build an insulated box around your mailbox and toss a heater in it.

It seems like it's not going to be an ideal situation.

[masraum]

https://goodmansonconstruction.com/concrete-curing/

Concrete curing, the hydration of the cement and the reaction between the cement and the water, is an exothermic reaction. Exothermic means it’s a reaction that gives off heat. This is very advantageous to pouring concrete in the cold. Depending on the mix and the additives, concrete starts generating its own heat right away.

The key for the best curing conditions in cold weather keeping the heat in so that the concrete remains at least 50 degrees while it cures.

Why is it so important to maintain proper curing temperature? Because if it gets too cold, the water in the cement will start to freeze and then the cement crystals don’t get hydrated enough and thus the concrete won’t cure properly. That’s bad news all around because if the concrete then dries out, you’ve got a lot of those cement crystals remaining dehydrated. The whole slab will have to be poured again.

We talk about this more in our blog on why concrete costs go up in winter, but suffice to say that the curing compounds in concrete need protection. And we provide that in the form of concrete blankets.

That’s why we put plastic sheets as insulation over the concrete to protect it. Our polystyrene insulation traps all that great exothermic heat in the concrete so that it stays warm enough to cure properly.

[dad911]

3rd generation mason/construction here. I've forgotten more than I remember, but I (we) would never lay block or pour outdoor concrete in those conditions. Blankets would help, but looking at your 10 day forecast, I would make him wait until next week.

[masraum]

Maybe you could put a coat on the mailbox and start a fire in a 55gal drum to keep it warm. Make sure that you send pics!

[KFC911]

Oh Yeah ..... Nope!

[flatbutt]

FWIW I was going to pour a pillar for my astro mount a couple of weeks ago but night temps were in the 40's. I decided to wait for spring as the pillar needs to be very strong. Mortar between bricks in a non bearing construct wouldn't seem to need much strength but I'd wrap it in a blanket of some sort to prevent the water from freezing. YMMV

[KFC911]

Originally Posted by flatbutt

FWIW I was going to pour a pillar for my astro mount a couple of weeks ago but night temps were in the 40's. I decided to wait for spring as the pillar needs to be very strong. Mortar between bricks in a non bearing construct wouldn't seem to need much strength but I'd wrap it in a blanket of some sort to prevent the water from freezing. YMMV

I don't think a blanket is gonna help much at 2 degrees and you're probably right, but.....

Naw...

[GH85Carrera]

OK, I think I will tell him to wait until after the "crazy cold" weather is past. It is not a urgent repair, but I don't want issues down the road.

[A930Rocket]

Originally Posted by KC911

I don't think a blanket is gonna help much at 2 degrees and you're probably right, but.....

Naw...

He needs an electric blanket!

Do they still make those?

[masraum]

Originally Posted by A930Rocket

He needs an electric blanket!

Do they still make those?

Absolutely.

[Noah930]

^^^ Tire warmers. We're car guys, right?

[wilnj]

As with everything else, it depends.

Cement does give off heat as it cures but it’s a function of mass and surface area.

When I pour a 300 or 400 yard footing that is on the ground, in a hole and it’s 4 or 6 feet thick, we can throw blankets on top, draped down to ground and it will be fine well below freezing.

If I do a 300-400 yard floor placement on metal deck, up on the building it’s only 3 to 6 inches thick, we have to enclose the floor where the work is taking place as well as the floor underneath and heat the floor underneath. I’ve been able to get 60 degree deck temperatures for those jobs even when the outside air temperature is at or below freezing.

In the OPs example, you have a ribbon of mortar, 3/8” thick and 3” wide surrounded by bricks that are 2-1/4” thick and 3-5/8” wide acting as a heat sink.


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[GH85Carrera]

I called off the brick work to today. It is currently 26, and it will maybe be above freezing for a few hours, and the low tonight is forecast to be 3. Ain't no way I want anything with water in it outside in that. This is not some mission critical hard deadline project. I can wait until after Christmas when the temps will be above freezing at night.

[island911]

Yeah, 26 - too damn cold to be working in.

Great time to go skiing.