laying brick in freezing temperatures


Old 01-31-00, 06:01 PM
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Late this afternoon I went by my new house which is under construction. The brick layers were laying brick and the temperature had not been above freezing for two consecutive days. The low for tonight is to be 24F. What could be the problems either short term or long term for laying brick in these temperatures?
Thanks ahead of time for your reply.
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Old 02-01-00, 11:16 PM
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I am the same Dale that posted the original response.

Skilled masons can and do lay brick during freezing temperatures. Underline: "skilled masons". A single mason, skilled or not, would rarely undertake anything more than a small repair under freezing conditions, due to the nature of the work. Extreme heat is another conditon that requires more than a little bit of skill plus addional help.

An to answer your question is not as simple as a list of possible defects. Less than desireable work is measured in degrees, not absolutes. Some defects can be seen, for others destructive tests would be used. I am not changing my opinion, but I will try to explain it more fully.

The 50 degree factor:
Like Portland Cement, Mortar sets by the process of Hydration (water combines chemically to form a solid). For Portland Cement the process of hydration slows at temperatures below 50 degrees and it will halt duing the process of freezing, which actually starts around 39 degress. The most critical time for hydration is the first three days, with day one being the most significant.

Unlike cement, mortar contains Lime, another material that hydrates. The addition of lime changes the temperature value to some degree but the same idea applies. Some masonary manuals suggest 40 degrees as the cut off temperature, however, I disagree, because mortar is a simple mixture and it contiunes to be one long before complete hydration occurs, and many mortars contain Portland Cement. Choosing 50 over 40 before makng temperature adjustments to the mix is the safer bet.

The scope:
It's desriable for mortar or concrete to initially set and gain strength rapidly through hydration. Low tempeartures slow hydaration and may arrest it, high temperatures speed hydration.
Hydration involves bound water. Free water (or excess water) imparts workability to the mix. In mortars, during cold weather work, free water must be kept to a minimum, because free water forms ice crystals more readily than bound water. On the other hand there must be enough free water in the mix for the inital suction bond between the Brick and Mortar to occur.

Ice crystals cause lack of bonding, weaker mortar, more porous mortar, slower hydration,
and shrink cracking. Typically shrink cracks show up within the first week. Another drawback of too much water is expansion on freezing.

When the joints are tooled care must be used not to tool too soon, to compact the mortar well, and not to leave ice crystals behind from a cold tool.

Brick is porous and usually must be whetted prior to laying to avoid too much suction.
Too much suction weakens the mortar, not enough results in lack of bonding. During cold weather they may be laid dry (after thawing) since suction is reduced by the cold, and whetting may cause surface ice or ice within (setting up internal stresses).

During or after the work, the work must be protected from drying winds, freezing, snow, rain, hail, and cold from frozen ground (for courses close to the ground). The typical period is 16 hours. The same time peirod that the masons are usually absent. An engineer must have spent a whole day working out that spec..

As you can imagine cold weather masory is for skilled masons only.
Some of the steps that may be used to counter cold weather:

Use of high early Portland Cement. Sets and gains strength early.
Use of dry hydrated lime to reduce water content of the mix.
Addition of Admixtures: antifreeze, "setting" accellerators, air entrainig agents (forms small bubbles to counter the affects of freezing).
Controling water content to around 6% of the cementious materials.
Heating the mix water, possibly the sand, and holding the mix above 40 degrees before placement.
Thawing units, laying them relatively dry, and heating them when the temperature dips.
Protecting the work during and/or afterward form cold and moisture.

A short list of possible defects:
Shrink cracking. Ususally more noticeable at vertical "head joints".
Weakened mortar. Hydration, too much water, high absorbsion,ice crystals and honeycombing, fractures, rapid loss of water from dry winds.
Extemely porous mortar same as above, tooling (too soon, hard, much, or ice crystals).
Spalled units water freezing internally.
Fractured units unequal drying and freezing.

When extreme temperatures are involved it usually takes more than one mason to exercise the necessary controls plus manage the assembly work. And I can't imagne a mason (skilled or not) electing cold weather masonary when it wasn't absolutely necessary.
"It's too cold" doesn't mean that it can't be done or that it shouldn't be done.

50 degrees is iffy, so start adjusting. A 10 or 11 degree temperature swing during unattend hours is not unheard of. And, as the temperature dips keep adjusting until the customer can't afford it.

I hope I have cleared up my opinion.
Old 02-18-00, 12:01 PM
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i'm a bricklayer that moved to so. cal because of those freezing temps.I'm not sure of the specific specs regarding temp but if you are able to lay the brick you're probly ok.The thing we worried about most was covering the brick for a few days so it would cure properly,either with plastic or tent and put heaters inside.I've been in so cal for 15 years so there might be better ways to do now

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