old cement

[Fred]

Hi,

I've been having a spring clean of my garage and found half a bag of mastercrete cement. I always buy cement in that brand because I figure the plastic bag must keep moisture out better than a paper bag; especially when it is used for infrequent DIY use. Or am I wrong about that?

The bag says use by September 2011. Should I throw it away? It is still powder; it has not set in one big lump. OTOH I think I read a post here once that said old cement would not set as strong. Is that right?

I haven't got any projects lined up, so I suppose it will be even more out of date by the time I come to use it. Perhaps I should just buy fresh when I need it? But you can bet the moment I throw it away, I will need it!

TIA

[Tim Watts]

Not lumpy is a good start - but the open bag will have admitted moisture laden air.

The results of this may be that the cement sets faster than usual.

In the worst case you can use it for less critical jobs - the least critical being "postcrete" where you could use any old s**te.

For other jobs, make a trial mix of a small amount and see how fast it sets.

[Andrew Gabriel]

I've never noticed any difference in setting time (unlike plaster). What I rather imagined is that some of the powder has effectively become already set cement. If this is the case, you can compensate by making a stronger mix, but you won't have any qualitative way to determine how much stronger, and it's probably not happened evenly thoughout the bag, so as Tim says, keep it for something non-critical.

[js.b1]

You can buy cheap 5L 20L 25L drums intended for liquid on Ebay - ok for finer free-running powders. Alternatively there are bigger 30L drums with wide neck, some with steel band fastening and seal quite well. Great for buying in bulk when you know the job is going to be "a bit at a time".

The sheds do plastic self seal tubs for cement & mortar, overpriced, but the tubs do keep stuff fresh and can be refilled with the lid remaining reliable.

Homebase... 12x25mm stripwood =A38.99... B&Q =A32.99... car park empty, more staff than customers, do not carry everything to complete a common DIY task... sigh.

[The Natural Philosopher]

That is broadly my experiences. You need a bit more cement to compensate for the bits that have already hydrated.

In the cement mixer, you tend to end up with large lumps that you can remove by hand, and a a lot of fine sized lumps, which rather replace the sand as the matrix, slightly weakening the final strength. That is really not an issue for most uses - if the bag can be mixed at all, a usable mortar results. If in doubt use some fresh as well. Overall setting time is not affected. either parts of the cement have set, or they haven't. They are not 'half set' in any meaningful way.

so unless you are casting stressed concrete members I would not be overly concerned. My experience is that either the bag is 90%+ usable ( makeye a crust round it which can be broken up ) or its 90%+ unsuable (its a fused mass of cement where its been exposed to a lot of damp).

The recoverable cement fom the latter case is too small to be worth the attempt.

[Brian Gaff]

Well, as long as it is indeed dry I'd imagine its not suddenly going to go off like a piece of food. Brian

[Andrew Mawson]

So far I've used three pallets of Mastercrete that was well out of date (several years) with no perceptible problem. But at £2 per bag and 180 bags you can afford to pop a bit more in the mix

AWEM

[NT]

Can I quote you three for a wiki page on this?

NT

[Andrew Gabriel]

We used to have a cement chemist in the newsgroup many years ago... I wonder what happened to John Schmitt?

His FAQ is still in the waybackmachine...

[The Natural Philosopher]

Of course.

I didnt think it was that unusual.

[Bill Wright]

Don't risk it. Sometimes it will set and look OK but it has no strength.

Bill

[NT]

Its all good material not yet on the wiki

NT

[Fred]

Thanks everyone. I shalln't be building any houses with it. I did fold the top of the bag over to try to limit exposure to damp air. The idea in another reply about using an airtight bucket is a good one.

I guess I may do some pointing if I get round to it; would that be ok?

Thanks again.