Bill Price looks at the issue of shelf-life and best before dates
As merchants who are selling cement and other cement-containing materials, you may have noticed cement bags have a use by date printed on them but might not be aware of its significance. This is in effect a ‘shelf life’ for cement and has a big impact on stock control both for your suppliers and your own outlets.
Products with an extended shelf life (particularly if they are slow moving lines), are much more attractive to merchants and minimise the risk of being left with large quantities of ‘out of date’ stock. This is increasingly important at times when demand is low.
However, there seems to be a lot of misunderstanding about meaning of the ‘shelf life’, so I’ll try and clarify things.
Cement contains minute quantities of a naturally occurring, soluble, form of chromium which, in a small number of people, causes an allergic reaction leading to a rather nasty skin condition called chromate allergic dermatitis.
The European REACH regulation, which now governs the safety of chemicals used in industry, stipulates that at the time the cement is hydrated (i.e. when water is added to it on site), the soluble chromium content should be less than 2 parts per million.
So, to reduce the risk of users developing dermatitis, the cement producers put an additive in the cement that keeps the chromium below a certain limit when water is added. However, some cements, such as white cement, are naturally low in soluble chromium and do not normally contain the additive.
Unfortunately, the additive doesn’t last forever and it degrades with time. This is what effectively controls the shelf life. If the additive doesn’t work, the level of soluble chromium in the wet mortar can be too high. The cement will often continue to set and harden normally after the end of the shelf life, but there is an increased risk of susceptible users developing dermatitis.
The degradation of the additive occurs when air and moisture percolates through the packaging, so less permeable packaging like plastic bags and tubs will contribute significantly towards an extended shelf life. Products with more permeable packaging may also need to be stored indoors.
It makes sense to stock plastic packed cement containing materials if you don’t want it to deteriorate on the shelf.
Bill Price (@ConcreteDrBill), National Commercial Technical Manager , Lafarge Cement