Cement shelf life

I want to fix (bodge) a fence post aand I've got some ready mixed mortar rhat must be a year or two old.
It looks perfectly good, but I understand that cement has a short shelf life, even if kept warm amd dry; however mine looks perfect.
Just for interest, if it does deteriorate, could anyone explain the mechanism - it would ease the pain of shelling out for a new bag!
Can anyone advise, please - I have tried googling, but the answers cover such a wide range I'm not much wiser, and John Scmitt's FAQs don't seem to answer this one.
mike
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mike ring wrote:

mortar
shelf
cover
seem to

should be ok. Normally it sets into a rock when its had it.
NT
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snipped-for-privacy@meeow.co.uk wrote in

That's what I thought, but considering the age I tried fixing a bit of pointing in my paving, and it doesn't seem to be going off.
I've checked the bag, and can't find a date on it, but 6 months is bandied about as a life.
But if *that's* so, how can I     be sure I'm buying fresh if there's no date?
And how long *should* it take to set hard - ish?
I can't bear to have it go wrong in front of the guy next door!
TIA
mike
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If there isnt a date on the bag, you cant tell how old it is. When it arrives on site and fresh, its hot, now dont laugh, because I can asure you its that hot even in the bag you cant touch it for much more than 5 seconds.
When concrete is poured on site. its recond to give it a day for every 1" or 25mm. to cure before stripping the shuttering off.

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     snipped-for-privacy@meeow.co.uk writes:

In my experience, it just gets steadily more and more lumpy, as opposed to starting off as a fine running powder.
--
Andrew Gabriel

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It absorbs moisture from the air and forms hard lumps. If it hasn't done this I still wouldn't recommend building a house with it but for a fence post go ahead. The worst it can do is refuse to set.
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That's the problem - it does seem to refuse to set, but I wanted to find out how long I need to wait.
It's been 24hrs and my test bit is still toffeeish, it wouldn't hold up a post.
I guess that means it's knackered, but with an undated bag, and it looking perfectly good, it's a bit hard for a muppet like me to tell.
mike
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done
It's dead :-)
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mike ring wrote:

Will take a couple of days at this temp to set hard.

Its fine. You are just impatient.
If it didn't turn to rock, its OK. I just used a half bag I had leftover from last year, and it went off allright in a coule of days, once I had sieved the rock hard lumps out of it and used a bit more than usueal for luck...
Oh by teh way, there is not size dependent cire time for concrete. Its only depebndeint on temperature. generally it sets overnight in summer, and about 2 nights in winter, to the level it feels 'hard' and takes on full strength over a couple of weeks.
It takes time to DRY OUT though...

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This is not true, cement powder loses its reactivity and you will end up with a weak matrix, not critical as far as a post mix is concerned but could be critical elsewhere. Cement is at its most reactive just after its manufactured and gets slower and weaker from then on. Just because it has set doesn't mean its strong.

You obviously don't work with structural concrete or even slabs that need to have achieved a certain strength before loading. Concrete has initial set (surface hard) and final set (hard all the way through), you are right to say that these can be dependant on temp but you can achieve a false surface set if you have severe drying conditions. The rate of strength gain of concrete is a well understood area and are usually measured at 1, 3, 7, and 28 day intervals.

--
David

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mike ring wrote:

Aren't you thinking of plaster?
David
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I dont think so. Plaster when its old sets as soon as youve mixed it and steams
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wrote:

I added some mortar plasticiser liquid, which I had lying around, to some old cement in a mix which kept it alive a bit longer. The bag was about 6months old and had been left open.
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No, Supamix dry mortar mix.
The bag says store in a dry place, which I have, but no mention at all of a shelf life or use by date.
mike
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The only way I've had cement go off on me was going hard or lumpy - whatever wasn't rock solid would always set. The only problem I've really had was with some Wickes exterior tile which is quick setting normally but wouldn't set after 6 months in the open bag. I wonder if what you have isn't plain old sand and cement but something more like my tile cement?
I'd give your test piece a bit more than 24 hours to go off though - give it another couple of days before you declare the stuff useless.
Andy.
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mike ring wrote:

What I meant was, it's well known and indisputable that plaster has a short shelf life, cos old stuff goes off far too quickly when you try to use it - I, for one, had never heard that cement has similar properties so I just wondered if you were confusing the two.
David
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No, it's the opposite. It refuses to set, it'e *still* not gone orf at all, just dried to a stiff stodge!
Of course, I've never played with plaster, I can't even work cement.
It's a dry mix of sand and cement to some BS part xyz, which I take to mean it should work.
It seems from googling to be assumed there is a shortish shelf life, but no-one has mentioned what it is, or why it dies while looking in good nick.
I'll have to go and get some more, but I'd really like to know what's going on
mike
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Cement will absorb moisture from the air and will hydrate (set) in the bag, often this will be seen as solid lumps but it can remain as a powder but will be a lot less reactive than new cement which is why it can take a long time to set and be fairly weak. I would get a new bag if its at all critical and I would count not losing face in front of your neighbour as being critical
--
David

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snipped-for-privacy@chapelhouse.demon.co.uk wrote in

Got to be what's happened - they could have warned me
>I would get a new bag if its at all critical and I would count not losing

Absolutely - he knows I can electrify and plumb (thanks to free tuition here); I can't have a newly-bodged post fall over in 20 mmins ;o)
mike
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Better still, give up the addiction to Ordinary Portland Cement and take up an enthusiasm for lime.
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