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Guru

Join Date: Jun 2007
Location: Northampton, Pennsylvania
Posts: 944
Good Answers: 28

Cement (mortar mix) shelf life

01/03/2008 9:29 PM

In getting ready for snow blower season, I wanted to repair good sized cracks in the sidewalk. Some of these had been repaired before and usually last four to five years before breaking up again. I don't have a problem with that.

Since the repairs are small, most are at slab divisions and are about two to six inches wide and "V" down to one to two inches deep across the width of the sidewalk, I have always successfully used mortar mix. I don't feel reinforcement or incorporation of aggregate is necessary in these small patches.

The problem came when I mixed about a half bag of mortar mix that I had stored in my cool and very dry basement since the last episode of patching. (four years ?)It gave me no problems at that time. This time I have problems.

Temperature was in the upper 40's F with an overnight forecast in the lower 30's with light rain/sleet. Snow was due in two days. This was my last chance to get it done. I filled one of the cracks with the old mix and had to buy another bag to take care of all the other cracks. Each was covered with plastic sheet to keep most of the moisture away from it. Overnight, some level of freezing probably occurred. In the morning, there was a layer of frost on top of most of the patches. So be it.

Now, two months later, all the patches from the new mix are solid. The patch with the old mix is very crumbly and sheds a thin layer each time there is a precipitation event. I'm not losing any sleep over it, I'll just re-pour it in spring, but I was wondering, does a well stored bag of cement have a shelf life?

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Power-User

Join Date: Jan 2007
Location: UK S.Northants
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#1

Re: Cement (mortar mix) shelf life

01/04/2008 8:50 AM

Yes it does. I was told when you buy it choose the warm one, as that is freshest. I do exactly the same thing (use old cement) I am glad to hear others do and would also love to hear an official (-sell by?) and unofficial (-use by) date for non-professionals from those in the know.

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Guru

Join Date: Jul 2007
Posts: 4469
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#2

Re: Cement (mortar mix) shelf life

01/04/2008 7:41 PM

Usually the problem is getting the stuff to bond well since the old crack is already hard and (often) dirty. Some people use a little muriatic acid to clean it up, but a safer approach is to just brush it well and use a latex patching mix.

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Join Date: Jun 2006
Location: Melbourne, DownUnder
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#3

Re: Cement (mortar mix) shelf life

01/05/2008 4:12 AM

As far as I'm aware there is no shelf life for a bag of cement. The problem is moisture, as it will start the hydration process. As long as it's air tight it should be fine for a life time.

Maybe there was a same amount of moisture that got into the "old" bag. Or you used a different water/ cement ratio. A 0.35 ratio is best.

For example. Pour a litre (1/4 gallon) of water into a bucket. Get a handful of cement (use gloves, face mask and glasses as it can give you chemical burns ). It may be best if you use a low-heat cement instead of the regular Portland General Purpose cement. Low heat also will take longer to set giving you more time to play.

Mix the cement into the bucket of water.

Add another handful of cement. Keep adding until you get a consistency of mayonnaise. Now use half a handful of cement and mix it in. The object is to get it just thick enough that when you grab a handful of mix and turn your hand upside down the mix will stick to your hand with a glue like consistency.

Once you lay the cement, keep it moist until it sets. Should be solid within a day no matter what temperature it is. Maximum strength is reached in 28 days. But I don't thick you need cement that has a Unconfined Compressive Strength of about 50 MPa.

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#4

Re: Cement (mortar mix) shelf life

01/05/2008 1:37 PM

All cement has a shelf life due to moisture. Ambient moisture starts the hydration in cement. It is almost impossible to keep a bag of cement totally dry. Even in an unopened bag it attracts moisture. The bags have a plastic liner between the paper but also has small holes to allow air to escape. Over time the cement attracts any moisture available and hydrates leaving less unactivated cement available to actually bond when mixed. The shelf life depends on the moisture the bag attracts. You can get an idea of the usefulness left by checking the corners of the bag to see if they are chunky or have hard lumps. If you find lumps when you go to mix it - you might as well through it away because it will do exactly as you found when you used it. I have found that keeping it as dry as possible will only save it for maybe 6 months.

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