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ovahimba 10-30-2009 03:53 PM

Bags of concrete left out in the weather
My project has taken me longer than anticipated and a pallet of concrete in 60 bags has been sitting outside for more than 6 months. It has been exposed to various amounts of moisture. The top bags have partially hardened. The clods however are easily pounded back to a powder with a mallet. How compromised is this concrete? Will it be significantly weaker even if I give it a good spin in the mixer? I'm using it for deck footings.

concretemasonry 10-30-2009 05:55 PM

Do you have bags of cement or bags of pre-proportioned concrete? If cement, it will not be as good as when it was new and it apparently was not worth protecting.

If it is pre-proportioned concrete the packaging is usually not as good and the concrete will definitely be substandard because the moisture may have made everything start to work and there will not much left for a fresh mix and you might have to add some fresh cement, but there is a limit to how much good it will do.

Fortunately for you, deck footings may not need much good concrete.

If it is cement, you can break the lumps (top of the top layer of bags and the corners of the others) to make them seen small enough. Because they have been exposed to the moisture, they have already been hydrating (curing into a low strength mush) that is really not reactive in a mix. Throw away any lumps (may be difficult in the green S.F. area) and try to get the most out of the other cement and increase or spike it with some fresh cement.


ovahimba 10-30-2009 07:43 PM

Thanks for the insight. The bags are pre-proportioned in that there is sand and gravel in the bags along with cement. I underestimated a recent storm and the tarp was blow off the top. The sides are wrapped in a saran wrap from the store which causes condensation occasionally. I might take off the top bags and deal with them last.

Bondo 10-30-2009 08:53 PM


I might take off the top bags and deal with them last.
Ayuh, or deal with 'em 1st, so they're at the Bottom of the hole, rather than at grade,....

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