Shelf life of plaster, cement

[xerxes]

I've learned to my cost in the past that old unused plaster, even though it still looks powdery, is useless and costs a lot of wasted time.

But how can I tell if plaster I bought a while ago and stored in a shed is still any good: is there a simple test?

The same question applies to cement. Clearly, if the bag's gone rock hard, it's beyond use, but what about the earlier stages when there are pea-sized lumps?

I'm trying to discipline myself to buy only what I need for small jobs, but I still waste quite a lot.

 

[JohnD]

Cement, if it is free from lumps that cannot easily be broken up in the fingers, is OK to use.

 

[roughcaster]

With the plaster, mix a drop up and see how long it takes to set.

Roughcaster.

 

[mattylad]

If its kept in a dry/sealed container would this prolong its storage life?

How long can you get out of it & does it differ between backing & finish ?

 

[xerxes]

Thanks for these replies. Roughcaster: how long would be a reasonable setting time?

 

[roughcaster]

Any plaster kept in damp conditons for a while will not keep. If you keep it in a polythene bag, it will keep a lot longer. Whether it's undercoat plaster or finishing, it'll be the same. Old plaster goes off much quicker,,, great if you use it for patching, but no use for the bigger areas. You would know within a few minutes or so whether it was going to stay workable, or whether it was dead. The approximate setting time for in date multi finish, so it says on the bag,is one and a half hours, undercoat plasters 1.5 to 2 hours. This varies with conditions, eg. hot/cold etc.....How long would be a reasonable setting time for older, badly stored plaster? If you can get half an hour or so out of it and that suits the size of the job, you'd be doing all right, but if it went off within a few minutes, it's no good at all. And don't forget, even if it's out of date, but it's been kept out of the damp, it'll still be a good bag to use.

Roughcaster.

 

[xerxes]

Thanks again: very helpful.